Chemistry Regents
Multiple Choice Answer Key

Electrons occupy the region outside the nucleus; protons and neutrons are inside it.

The deflection of a small fraction of alpha particles indicated a concentrated positive charge at the atom's center.

Both protons and neutrons have a mass of approximately 1 atomic mass unit (u).

Electrons in higher shells are farther from the nucleus and possess greater potential energy.

Electrons must absorb energy to jump to a higher energy level, producing the excited state.

Chemical properties describe how a substance undergoes chemical change; reactivity with oxygen is a chemical property.

Both are pure carbon, but their atoms are arranged differently, giving rise to different properties (allotropes).

First ionization energy increases across a period; neon, a noble gas with a full valence shell, has the highest value in Period 2.

By definition, a compound always consists of elements joined chemically in a fixed, definite ratio.

A structural formula explicitly shows how atoms are bonded and arranged within a molecule.

Equal volumes of different gases at STP contain the same number of molecules but have different molar masses, so their masses differ.

Compounds are classified as either ionic (formed by electron transfer) or molecular/covalent (formed by electron sharing).

O₂ contains a double bond (sharing 4 electrons) between the two oxygen atoms, which is a multiple covalent bond.

Methane has a perfectly symmetrical tetrahedral shape with uniformly distributed charge, making it nonpolar.

Bond formation always releases energy, as the bonded state is lower in energy than the separated atoms.

Fluorine has the highest electronegativity of all elements on the periodic table.

Heat always flows spontaneously from a warmer object to a cooler one; 15°C is the only option lower than 20°C.

The kinetic molecular theory assumes ideal gas particles exert no attractive or repulsive forces on each other.

At STP, equal volumes of any ideal gas contain the same number of particles; both He and Ar are monatomic, so equal volumes have equal atom counts.

At equilibrium, the forward and reverse reactions proceed at the same rate, so concentrations remain constant.

Heat of reaction equals the potential energy of products minus the potential energy of reactants (ΔH = PE products − PE reactants).

Vaporization increases disorder significantly as particles spread out and move more freely in the gas phase.

Natural systems spontaneously move toward lower potential energy and greater entropy (disorder).

1-hexene contains only carbon and hydrogen atoms; the other options contain oxygen or iodine, making them non-hydrocarbons.

Oxidation (loss of electrons) always occurs at the anode in any electrochemical cell.

H₂SO₄ is a strong acid that dissociates into ions in solution, making it an electrolyte; the others are nonelectrolytes or molecular compounds.

An Arrhenius acid produces H⁺ ions in aqueous solution; HCl dissociates to yield H⁺ and Cl⁻.

According to the Brønsted-Lowry theory, an acid is a proton (H⁺) donor.

Alpha particles consist of 2 protons and 2 neutrons, giving them the greatest mass and ionizing power of all nuclear emissions.

Nuclear fission releases enormous amounts of energy from very small quantities of fissionable material, which is its primary benefit.

The mixture's spectral lines match the combined lines of elements L and J, since each element produces a unique set of lines.

Noble gases are monatomic at STP, so the correct diagram shows single, identical, well-separated atoms.

Accepted density of Cu = 8.96 g/cm³; % error = |9.46 − 8.96| / 8.96 × 100 ≈ 5.0%.

Mg(24) + 2×N(14) + 6×O(16) = 24 + 28 + 96 = 148 g/mol.

Losing one electron reduces electron-electron repulsion, causing the ion to be smaller than the neutral atom.

F⁻ has gained one electron, giving it 10 electrons with the configuration 2-8, identical to neon.

Barium is an element and cannot be broken down further by chemical means; the others are compounds.

Filtration works because sand particles are too large to pass through filter paper while water molecules are not.

Table F indicates calcium phosphate is insoluble, while sodium carbonate and sodium sulfide are soluble.

M = moles/liters = 0.125 / 0.200 = 0.625 M.

A higher solute concentration causes greater freezing point depression and boiling point elevation.

°C = K − 273 = 35 − 273 = −238°C.

Boyle's Law states P and V are inversely proportional at constant T, producing a hyperbolic curve on a P vs. V graph.

This is sublimation — a phase change in which the substance's identity does not change, making it a physical change.

Powdered zinc provides greater surface area and 2.0 M HCl is more concentrated — both factors maximize reaction rate.

Iron changes oxidation state from 0 to +3 (oxidized) and oxygen from 0 to −2 (reduced), confirming it is a redox reaction.

Reduction is the gain of electrons; Na⁺ gains one electron to become neutral Na.

Each pH unit change represents a 10-fold change; a decrease of 2 pH units means [H₃O⁺] increases by 10² = 100.

Electroplating requires an external power source (electrolytic cell) to drive a non-spontaneous chemical change.

Fusion combines light nuclei (hydrogen isotopes) into a heavier nucleus (helium); the other options show fission or decay.

The deflection of alpha particles in Rutherford's experiment led to the nuclear model of the atom.

In the wave-mechanical model, an orbital defines the region of highest probability for finding an electron.

When electrons fall to a lower energy level, the energy difference is released as a photon of light.

Isotopes of the same element have identical atomic numbers (protons) but differ in the number of neutrons.

Reactivity with water describes how sodium undergoes a chemical change, making it a chemical property.

O₂ and O₃ are allotropes of oxygen with different bonding arrangements, resulting in different chemical and physical properties.

KCN contains the cyanide ion (CN⁻), which is a polyatomic ion composed of two different atoms.

A structural formula shows how atoms are connected and arranged, which a molecular formula does not convey.

Both charge and mass are conserved in chemical reactions; among the options given, charge is conserved in all reactions.

Coefficients in a balanced equation represent the relative number of moles of each substance involved in the reaction.

Titanium is a metal; metallic bonding (delocalized electrons in a lattice) exists only in metals and metallic compounds.

N₂ contains a triple bond, meaning 3 pairs (6 electrons total) are shared between the two nitrogen atoms.

Water has a bent shape with lone pairs on oxygen, creating an asymmetrical, polar charge distribution.

Breaking a bond always requires energy input (endothermic process); the I–I bond is broken here.

Electronegativity difference directly indicates how unevenly electrons are shared, determining bond polarity.

An aqueous solution of KNO₃ is a homogeneous mixture of KNO₃ dissolved in water.

Density is an intensive property that does not depend on sample size and remains constant for a pure substance.

Atomic number (number of protons) defines the element; all atoms of the same element have the same atomic number.

Pure water has a higher freezing point (0°C vs. below 0°C) and higher boiling point than a KI solution — wait, this is reversed: the solution has a lower freezing point and higher boiling point than pure water, so pure water has a HIGHER freezing point and LOWER boiling point. Answer is (4): higher boiling point (incorrect) — actually pure water has a LOWER boiling point than... No: solute raises BP and lowers FP of the solution, so pure water has higher FP and lower BP than the solution. Answer: (4) higher boiling point — this option says water has higher BP AND higher FP, which is wrong for BP. The correct answer is (2): lower boiling point and higher freezing point.

KMT states ideal gas particles move in straight lines randomly until they collide with each other or container walls.

Collision theory states that reactions occur only when particles collide with sufficient energy and the correct geometric orientation.

At STP, equal volumes of any ideal gas contain the same number of molecules (Avogadro's Law).

At 75°C, propanone has the highest vapor pressure on Table H, indicating the weakest intermolecular forces.

Water molecules form hydrogen bonds between the partially positive H of one molecule and the partially negative O of another.

Sublimation converts a solid directly to gas, dramatically increasing particle disorder (entropy).

Natural systems spontaneously move toward lower potential energy and greater disorder (higher entropy).

Ethyne (acetylene) is an alkyne; the general formula for alkynes is CₙH₂ₙ₋₂.

In a redox reaction, the number of electrons gained must equal the number of electrons lost (conservation of charge).

An Arrhenius base produces OH⁻ ions in aqueous solution; Ca(OH)₂ dissociates to yield Ca²⁺ and OH⁻.

The primary benefit of fission is its ability to generate enormous amounts of energy for electricity production.

Mass ≈ protons + neutrons; E has 50 + 70 = 120, the greatest of all four ions.

All digits in 20.40 are significant: 2, 0, 4, and the trailing zero after the decimal point.

Each oxygen is −2; with two oxygens (total −4), lead must be +4, giving lead(IV) oxide.

The empirical formula is the simplest whole-number ratio; C₂H₆ reduces to CH₃.

By conservation of mass: mass of O₂ = mass of products − mass of CO = 8.8 − 5.6 = 3.2 g.

Each element's atomic mass is multiplied by its subscript: C=12, H=1, N=14, O=16.

Table F shows calcium bromide is soluble, while the other options (lead sulfate, silver carbonate, tin hydroxide) are insoluble or slightly soluble.

Table G shows NaCl solubility at 20°C is approximately 36 g/100g water; 30 g is at or near the saturation point making a saturated solution.

ppm = (mass solute / mass solution) × 10⁶ = (0.050 / 2000.) × 10⁶ = 25 ppm.

Heat flows from the warmer cup (44°C) to the cooler hand (37°C), as heat always flows from hot to cold.

q = m × Hf = 26.2 g × 334 J/g ≈ 8750 J = 8.75 × 10³ J (using Hf of water = 334 J/g from Table B).

During a phase change (plateau), temperature and average KE are constant while potential energy decreases as bonds form.

A saturated hydrocarbon contains only single carbon-carbon bonds; the correct diagram shows a fully saturated alkane.

When Br₂ adds across a carbon-carbon double bond, the double bond opens and both Br atoms attach — this is an addition reaction.

In SO₂, each O is −2 (total −4); sulfur must be +4 to make the molecule neutral.

A higher concentration of ions produces greater conductivity; 1.0 M CaCl₂ has the highest ion concentration.

Neutralization of a base with nitric acid produces a salt (strontium nitrate) and water.

Water donates an H⁺ to ammonia, acting as a Brønsted-Lowry acid in this reaction.

Beta decay occurs when a neutron converts to a proton, emitting a beta particle (electron); carbon-14 decaying to nitrogen-14 fits this pattern.

A combines light nuclei (fusion); B splits a heavy nucleus (fission).

Both protons and neutrons have a mass of approximately 1 u; electrons are about 1/1836 of that mass.

When an electron absorbs energy and moves to a higher shell, the atom is in an excited state (not ionized, so still an atom).

Isotopes of the same element always have the same number of protons but differ in neutron count.

O₂ and O₃ are allotropes — they have different molecular structures and consequently different physical and chemical properties.

A compound is formed when two or more different elements are chemically bonded together in fixed ratios.

Both charge and mass are conserved in chemical reactions; charge is always conserved.

Iron is a metal and exhibits metallic bonding through a sea of delocalized electrons in a crystal lattice.

Forming a cation removes an electron, reducing electron-electron repulsion and shrinking the ionic radius.

Bond formation is always exothermic; energy is released when two fluorine atoms combine to form F₂.

Radon is a noble gas with a completely filled valence shell, giving it a stable electron configuration.

Electronegativity is defined as the measure of an atom's ability to attract shared electrons toward itself in a bond.

NaCl is a pure substance (compound) with a fixed composition and uniform properties — it is not a mixture.

Selenium is an element; all its atoms have the same atomic number (34), unlike compounds which contain multiple elements.

Distillation separates liquids based on differences in boiling points, allowing the more volatile component to be collected separately.

Dissolving KCl depresses the freezing point and elevates the boiling point of the solution compared to pure water.

Thermal energy is a form of energy associated with the motion of particles; molarity, temperature, and volume are not forms of energy.

Average kinetic energy depends only on temperature, not mass; 40°C is the highest temperature listed.

At low pressure and high temperature, gas particles are far apart with minimal intermolecular interactions, approximating ideal behavior.

KMT assumes ideal gas particles have no intermolecular attractive or repulsive forces.

Collision theory requires that reacting particles must collide with both proper orientation and sufficient activation energy.

At equilibrium, forward and reverse rates are equal, so concentrations stop changing and remain constant.

All catalysts, including enzymes, lower the activation energy required for a reaction, allowing it to proceed faster.

Carbon's tetravalency and ability to form strong C–C bonds allows it uniquely to form the vast variety of chain, ring, and network structures found in organic chemistry.

Amines contain nitrogen; the "-amine" suffix indicates the presence of an –NH₂ functional group containing nitrogen.

Ethyne (HC≡CH) has a triple bond between the two carbons, meaning 6 electrons (3 pairs) are shared.

Reduction is defined as the gain of electrons (remember: LEO the lion says GER — Gain Electrons = Reduction).

According to Table M, methyl orange is red below pH 3.2, so only pH 2.7 falls in the red range.

Gamma radiation has the greatest penetrating power, followed by beta particles, then alpha particles which are stopped by paper.

The primary benefit of nuclear fission is its use in power plants to generate large amounts of electrical energy.

Nuclear reactions involve mass-energy conversion (E = mc²) and release millions of times more energy per mole than chemical reactions.

Accepted density of Fe = 7.87 g/cm³; % error = (7.57 − 7.87) / 7.87 × 100 ≈ −4.0%.

As atomic number increases in Group 17, molecular size and London dispersion forces increase, raising the boiling point.

Aluminum replaces iron in the compound, fitting the pattern A + BC → AC + B of a single replacement reaction.

NaCl is soluble in water while AgCl is insoluble; solubility can be used to distinguish them without changing their identity.

Neon is a monatomic noble gas; at 35 K and 1.0 atm it is a gas with individual atoms well separated from each other.

HCl has a larger electronegativity difference between H and Cl than HBr; H₂ and F₂ are nonpolar since both atoms are identical.

q = mcΔT = 130. g × 4.18 J/g·°C × 30.0°C = 16,302 J ≈ 1.63 × 10⁴ J.

Equal numbers of gas particles require identical P, V, and T conditions (ideal gas law: PV = nRT).

This represents a phase equilibrium (gas ⇌ solid) — a physical change with no new substances formed.

Increasing temperature favors the endothermic (reverse) reaction; for this exothermic reaction, equilibrium shifts left, decreasing SO₃.

Vaporization converts a liquid to a gas, greatly increasing particle disorder (entropy increases).

An unsaturated hydrocarbon contains at least one carbon-carbon double or triple bond.

Fermentation of glucose (C₆H₁₂O₆) produces ethanol and carbon dioxide; this is the standard fermentation reaction.

Combustion involves rapid reaction with oxygen to produce CO₂ and H₂O; methanol burning fits this definition.

In a redox reaction, electrons lost must equal electrons gained; 2.0 mol lost = 2.0 mol gained.

NaOH is an Arrhenius base (produces OH⁻), and its ions make the solution a conductor of electricity.

In 0.020 M, leading zeros are not significant, but the 2 and the trailing zero after it are; that gives 2 significant figures.

From the balanced equation, 3 moles of O₂ are used for every 2 moles of CO₂ produced, giving a 3:2 ratio.

Electroplating uses an electrolytic cell where external electrical energy drives a non-spontaneous chemical reaction.

H₂O accepts H⁺ in the forward reaction to form H₃O⁺, and SO₄²⁻ accepts H⁺ in the reverse reaction to form HSO₄⁻.

The nucleus contains protons and neutrons; electrons are found in shells outside the nucleus.

Protons are positive and electrons are negative; in a neutral atom they are equal in number, giving a net charge of zero.

In the wave-mechanical (quantum) model, orbitals define the regions of highest probability for finding electrons.

Isotopes share the same atomic number (protons) but differ in mass number due to different neutron counts.

O₂ reacts with sodium to form sodium oxide, while He is chemically inert; this chemical property differentiates them.

O₂ and O₃ are allotropes of oxygen with distinct molecular structures and therefore different physical and chemical properties.

Ammonia (NH₃) is a compound that can be decomposed into nitrogen and hydrogen by chemical means; the others are elements.

Zinc is a metal; metallic bonding — a lattice of positive ions surrounded by delocalized electrons — holds it together.

Methane has a symmetrical tetrahedral shape; bond dipoles cancel out, making it a nonpolar molecule overall.

Bond formation is always exothermic; the system releases energy as the two fluorine atoms bond together.

Electronegativity decreases down a group; oxygen at the top of Group 16 has the highest electronegativity.

A dissolved salt in water forms a solution, which is a homogeneous mixture with uniform composition throughout.

An aqueous solution is a mixture; the ratio of KBr to water can be varied, unlike pure substances with fixed composition.

KMT states ideal gas particles move in constant, random, straight-line motion between collisions.

Collision theory requires sufficient activation energy along with proper orientation for a reaction to occur.

By Avogadro's Law, equal volumes of gases at the same T and P contain equal numbers of molecules.

Table I shows the heat of formation of ethane is negative (−84.7 kJ/mol), indicating an exothermic reaction.

Increasing surface area exposes more reactant particles to collisions, increasing reaction rate; the other options are not rate factors.

Heat of reaction (ΔH) = PE(products) − PE(reactants); this determines whether the reaction is exothermic or endothermic.

Catalysts work by offering an alternative mechanism with a lower energy barrier (activation energy), speeding up the reaction.

Natural systems spontaneously move toward minimum energy and maximum entropy (disorder).

Carbon's unique ability to form four strong covalent bonds allows it to create the diverse chains, rings, and networks found in organic chemistry.

Alcohols contain the −OH (hydroxyl) functional group; the "-ol" suffix identifies 1-propanol as an alcohol.

Isomers share the same molecular formula (C₄H₁₀) but have different structural arrangements of atoms.

Ethene (C₂H₄) has a double bond and ethyne (C₂H₂) has a triple bond; both contain multiple covalent bonds.

Substitution is a type of organic reaction; deposition, solidification, and vaporization are physical changes, not organic reactions.

This is a fundamental rule of electrochemistry: An Ox (Anode = Oxidation) and Red Cat (Reduction = Cathode).

When an Arrhenius acid reacts with an Arrhenius base, the products are a salt and water — this is a neutralization reaction.

Fission splits heavy nuclei (like uranium) into smaller nuclei; fusion is the opposite — combining light nuclei.

In fission, a small amount of nuclear mass is converted to enormous amounts of energy via Einstein's E = mc².

Mass ≈ protons + neutrons = 12 + 13 = 25 u (electrons contribute negligible mass).

The mixture containing element X must show all of X's spectral lines; Mixture C contains lines matching element X's spectrum.

Valence electrons are in the outermost shell; the configuration 2-8-18-3 has 3 electrons in the outermost shell.

Across a period, increasing nuclear charge pulls electrons closer (smaller radius) and more strongly (higher electronegativity).

ClO₂⁻ is the chlorite ion; combined with potassium (K⁺), the compound is potassium chlorite.

CH₃COOH has 2 oxygen atoms: 2 × 16 = 32 g/mol O; % = (32/60) × 100 ≈ 53%.

A double bond shares 4 electrons (2 pairs) between two atoms.

Neon is a monatomic noble gas that exists as separate single atoms at STP in the gaseous state.

150.0 has four significant figures: 1, 5, 0, and the trailing zero after the decimal point.

Heat flows from the hotter copper (100°C) to the cooler water (20°C) until thermal equilibrium is reached.

Phase equilibrium between liquid water and water vapor requires a closed system; sealing the flask traps the vapor.

From Table I, the heat of formation of NH₃ is −91.8 kJ/mol for 2 mol; per 1 mol = 91.8/2 = 45.9 kJ released.

Sublimation absorbs energy (endothermic) and converts ordered solid to disordered gas (entropy increases).

Oxidation is the loss of electrons; manganese loses electrons to become Mn²⁺, which is an oxidation half-reaction.

Carbon changes from 0 to +4 (oxidized) and oxygen from 0 to −2 (reduced), making this a redox reaction.

A metal reacts spontaneously with an ion if it is above that ion's metal on Table J (activity series); Mg is more active than Fe.

NaNO₃ is soluble and dissociates into ions; the others (CaCO₃, BaSO₄, Mg(OH)₂) are insoluble and produce very few ions.

HSO₃⁻ donates a proton (H⁺) to water, acting as a Brønsted-Lowry acid in the forward reaction.

1000 = 10³ times more H₃O⁺ means the pH decreases by 3 units: 5.0 − 3 = 2.0.

A well-known risk of nuclear fission power plants is the generation of radioactive waste that requires long-term storage.

Dalton proposed the hard sphere model, Rutherford discovered mostly empty space with a nucleus, and Bohr placed electrons in shells.

Electrons in higher shells (farther from the nucleus) possess greater potential energy than those in lower shells.

The energy difference between levels is released as a photon of light with a specific frequency when an electron drops to a lower shell.

Atomic mass is calculated from the masses and natural abundances of all naturally occurring isotopes of an element.

The modern periodic table organizes elements by increasing atomic number (number of protons), not atomic mass.

Tellurium is a metalloid found on the staircase boundary of the periodic table; Ba and Cs are metals, Xe is a noble gas.

Sodium is highly reactive (especially with water) while gold is largely inert — reactivity is a chemical property.

A compound is defined as a pure substance made of two or more elements chemically bonded in a definite, fixed ratio.

Coefficients in a balanced equation represent the relative number of moles of each reactant and product.

Bond formation always releases energy (exothermic); the bromine atoms combine to form Br₂ releasing energy.

The difference in electronegativity between two atoms determines how unevenly electrons are shared, and thus bond polarity.

Aqueous ammonia is a solution (mixture); the ratio of ammonia to water can be varied, unlike pure substances.

Electromagnetic radiation is a form of energy; pascal is a unit of pressure, molarity a concentration unit, and temperature a measure of average KE.

KMT describes ideal gas particles as moving in constant, random, straight-line paths between elastic collisions.

Collision theory requires both sufficient activation energy and the correct geometric orientation for a reaction to proceed.

Avogadro's Law: equal volumes of gases at the same temperature and pressure contain equal numbers of molecules.

The physical state (solid, liquid, gas) is determined by how molecules are arranged and how strongly they interact.

Powdered zinc maximizes surface area and 2.0 M HCl maximizes concentration — both factors increase reaction rate.

Heat of reaction (ΔH) represents the net energy absorbed or released when reactants are converted to products.

Natural processes spontaneously move toward minimum energy and maximum entropy (greater disorder).

The prefix "non-" means nine; nonane is the straight-chain alkane with 9 carbon atoms.

2-butyne contains a carbon-carbon triple bond, making it an unsaturated hydrocarbon (alkyne).

Ethene (C₂H₄) has a C=C double bond; a double bond consists of 4 shared electrons (2 pairs).

Substitution and polymerization are both types of organic reactions; solidification and vaporization are physical changes.

Oxidation (loss of electrons) always occurs at the anode in any electrochemical cell, electrolytic or voltaic.

By Arrhenius definition, a base produces OH⁻ (hydroxide) ions when dissolved in water.

pH = −log[H₃O⁺]; a 10-fold increase in [H₃O⁺] decreases the pH by exactly 1 unit.

Both U-235 and U-238 undergo alpha decay, but they have very different half-lives (U-235: 7.04×10⁸ y; U-238: 4.47×10⁹ y).

In fission, a tiny amount of nuclear mass is converted to enormous energy via E = mc², as described by Einstein.

Radioactive waste from nuclear fission remains hazardous for thousands of years and requires careful long-term storage.

Electrons are negatively charged and are attracted toward the positively charged plate.

Neon's ground state is 2-8; any configuration where an electron has moved to a higher shell (like 2-7-1) is an excited state.

Forming XCl₃ means X has a valence of 3; Group 13 elements have 3 valence electrons and typically form +3 ions.

moles = mass / GFM = 238 / 56.1 ≈ 4.24 mol.

M = moles / liters = 0.60 / 3.5 ≈ 0.17 M.

Dissolving any solute in water depresses the freezing point below 0°C (freezing point depression).

Real gases approach ideal behavior at the highest temperature and lowest pressure, minimizing intermolecular interactions.

Using the combined gas law: P₂ = P₁V₁T₂/(V₂T₁) = (50.0)(30.0)(300.) / (60.0)(200.) = 37.5 kPa.

Catalysts work by offering an alternate mechanism with a lower energy barrier, allowing more collisions to be successful.

At the highest temperature, nitrogen gas particles move fastest and are most disordered, giving the greatest entropy.

The –NH₂ group identifies an amine and the –COOH group identifies an organic (carboxylic) acid functional group.

In redox reactions, electrons lost by one species must be gained by another; 2 mol lost = 2 mol gained.

Elemental aluminum starts at 0; in Al₂O₃ it has an oxidation state of +3 (since O is −2 and formula must be neutral).

Neutralization of Ca(OH)₂ with H₂SO₄ produces calcium sulfate (CaSO₄) and water.

Transmutation occurs when one element changes into another; oxygen-15 becomes nitrogen-15 by positron emission.

Fission splits a heavy nucleus (U-235) into lighter nuclei using a neutron, releasing additional neutrons and energy.

When two or more reactants combine to form a single product, the reaction is a synthesis (combination) reaction.

Distillation uses boiling, condensing, and collecting to separate liquids based on different boiling points.

In the forward reaction, CO₃²⁻ accepts a proton from water to form HCO₃⁻, acting as a Brønsted-Lowry base.

From the graph, 20.0 mg decreases to 10.0 mg (half the original) after 10.0 days, which is by definition the half-life.

The modern wave-mechanical model describes electrons as having both particle and wave properties, found in orbitals.

The nucleus of any atom contains protons and neutrons; electrons are in orbitals outside the nucleus.

In the electron cloud (wave-mechanical) model, orbitals represent the regions of highest probability for finding electrons.

Silicon has atomic number 14, meaning each silicon atom contains exactly 14 protons.

Chemical properties describe how a substance changes chemically; reactivity with hydrogen sulfide is a chemical property of silver.

O₂ and O₃ are allotropes with different bonding arrangements, resulting in different molecular structures and properties.

Structural formulas show atomic arrangement and bonding; empirical formulas show the simplest whole-number ratio of atoms.

The laws of conservation of charge, mass, and energy all hold in every chemical reaction.

Metallic bonding is characterized by a "sea" of mobile, delocalized valence electrons throughout a metal lattice.

Ammonia has a trigonal pyramidal shape with an asymmetric charge distribution due to the lone pair, making it polar.

Bond formation always releases energy (exothermic process); F₂ forms from two F atoms with energy release.

Solid and liquid NaCl are in different phases and have different physical properties such as density and particle arrangement.

Manganese is an element and cannot be chemically broken down further; ethene, propanal, and water are compounds.

Aqueous glucose is a solution (mixture); the concentration of glucose can be varied, so proportions are not fixed.

Ideal gas behavior is best approximated at low pressure and high temperature, minimizing intermolecular forces.

A key assumption of KMT is that ideal gas particles experience no intermolecular attractive or repulsive forces.

Collision theory states that reactions occur only when particles collide with sufficient energy and the correct orientation.

Cooling reduces particle speed, which decreases both the force of individual collisions and how often they occur.

Equal volumes of gases at the same T and P contain equal numbers of particles; Ne and Ar both give 5.4 × 10²² atoms.

At equilibrium, forward and reverse rates are equal, so concentrations remain constant (not necessarily equal).

ΔH = PE(products) − PE(reactants); a negative result indicates exothermic, positive indicates endothermic.

Catalysts function by providing an alternate mechanism (pathway) with lower activation energy, not by changing the energy of reactants or products.

The second law of thermodynamics states natural systems tend toward minimum energy and maximum entropy.

Organic compounds contain carbon bonded to hydrogen; CH₃Cl (chloromethane) is an organic compound, while the others lack carbon-hydrogen bonds.

This is a fundamental rule: Anode = Oxidation, Cathode = Reduction (An Ox, Red Cat).

Fluorine has the highest electronegativity of all elements and is the most reactive nonmetal on the periodic table.

Ca(OH)₂ dissociates into Ca²⁺ cations and OH⁻ (hydroxide) anions; hydroxide is the only negative ion produced.

Neutralization of an Arrhenius acid (H⁺ donor) with an Arrhenius base (OH⁻ donor) always produces a salt and water.

Nuclear stability depends on the neutron-to-proton ratio; isotopes with ratios outside the stable range tend to be radioactive.

An alpha particle consists of 2 protons and 2 neutrons (mass ≈ 4 u), making it by far the most massive nuclear emission listed.

Phosphorus (Z=15) has configuration 2-8-5; 5 valence electrons in the outer shell and 10 non-valence electrons in inner shells.

Neutrons = mass number − protons = 112 − 48 = 64 neutrons.

Across Period 2, increasing nuclear charge pulls electrons closer to the nucleus, decreasing atomic radius.

ClO₃⁻ is the chlorate ion; combined with sodium (Na⁺), the compound is sodium chlorate.

O₂ contains a double bond between the two oxygen atoms, sharing 4 electrons (2 pairs).

From the equation, 3 mol O₂ produces 2 mol Al₂O₃; 12 mol O₂ × (2 mol Al₂O₃ / 3 mol O₂) = 8 mol Al₂O₃.

Empirical formula mass of CH₂ = 14 g/mol; 112/14 = 8; molecular formula = 8 × CH₂ = C₈H₁₆.

Water has strong hydrogen bonding, giving it stronger intermolecular forces than ethanol, resulting in a lower vapor pressure.

HF has the greatest electronegativity difference between H and F of any listed pair, giving it the most polar bond.

Table F shows CaS is soluble, while CaCO₃, CaSO₄, and CaCrO₄ are insoluble or slightly soluble.

A higher concentration of HCl means more H⁺ ions available per unit volume, increasing the frequency of effective collisions.

Sublimation converts an ordered solid to a disordered gas, significantly increasing entropy.

A compound with a carbonyl group (C=O) within a carbon chain is a ketone; the name depends on the position of the carbonyl group.

This is a halogenation (substitution) reaction; one H on methane is replaced by Cl, giving chloromethane (CH₃Cl) and HCl.

Fermentation is the anaerobic breakdown of glucose by yeast, producing ethanol (C₂H₅OH) and carbon dioxide.

Conservation of charge in redox: electrons lost by Sn²⁺ (2 mol) must equal electrons gained by Fe³⁺ (2 mol).

Higher ion concentration produces greater conductivity; 0.1 M LiCl has the highest concentration of Li⁺ and Cl⁻ ions listed.

Water donates a proton (H⁺) to ammonia in this reaction, acting as a Brønsted-Lowry acid.

Both Kr-85 and K-42 undergo beta decay, but their half-lives differ significantly (Kr-85: 10.76 y; K-42: 12.36 h).

In fission, the small loss of nuclear mass (mass defect) is converted to enormous amounts of energy via E = mc².