4 MAXE 012 MEHC
Portland State University
● ●
PSU Department of Chemistry — CHEM 210 Chapters 8–9
LET KNOWLEDGE SERVE THE CITY
CHEM 210
CHEM 210 — Examination 4 (Chapters 8–9)
GAS LAWS, KINETIC MOLECULAR THEORY, THERMODYNAMICS & CALORIMETRY | 2026/2027
INSTITUTION Portland State University (PSU) COURSE CODE CHEM 210 — Chapters 8–9
PROGRAM Undergraduate Chemistry / Pre-Professional ACADEMIC YEAR
EXAM TITLE Examination 4 — Gases & Thermochemistry TOTAL QUESTIONS 25 Questions
SUBJECT AREAS Gas Laws, KMT, Thermodynamics, Calorimetry, FORMAT Multiple Choice — Select the Single Best Answer
Enthalpy
EXAMINATION INSTRUCTIONS
▸ Select the single best answer for each multiple-choice question.
▸ Topics include: gas laws (Boyle's, Charles', Amonton's/Gay-Lussac's, Avogadro's, Combined, Ideal), kinetic molecular theory, Dalton's law of partial pressures,
Graham's law of effusion, and gas density.
▸ Thermodynamics: first law, enthalpy, calorimetry, Hess's law, standard enthalpy of formation, bond energy, and lattice energy.
▸ Temperature must be in Kelvin for all gas law calculations. Standard pressure = 1 atm = 760 mmHg = 760 torr.
▸ Correct answers and detailed rationales appear below each question for exam review purposes.
SECTION I — GAS LAWS, PRESSURE & KINETIC MOLECULAR THEORY Questions 1 – 14
1. What is the formula for pressure?
A. Force × Area
B. Force / Area
C. Mass / Volume
D. Density × Volume
CORRECT ANSWER B — Pressure = Force / Area; the SI unit is the pascal (Pa) = N/m²
RATIONALE Pressure is defined as force per unit area (P = F/A). In the context of gases, pressure results from molecular collisions with container walls. Standard
atmospheric pressure (1 atm) = 760 mmHg = 760 torr = 101,325 Pa. Hydrostatic pressure is pressure exerted by a fluid due to gravity. Option A is the
inverse (F × A would be force multiplied). Option C (mass/volume) is density. Option D (density × volume) gives mass. Understanding pressure units
and conversions is essential for all gas law calculations.
2. Standard atmospheric pressure (1 atm) supports a column of mercury exactly how high?
A. 100 mm
B. 500 mm
C. 760 mm — 1 atm = 760 mmHg = 760 torr
D. 1000 mm
CORRECT ANSWER C — 760 mmHg = 760 torr = 1 atm; this is the standard atmospheric pressure at sea level
RATIONALE Standard atmospheric pressure was originally defined by Torricelli's mercury barometer — the height of mercury that atmospheric pressure can
support. 1 atm = 760 mmHg = 760 torr (named after Torricelli). This is equivalent to 101.325 kPa or 14.7 psi. The mmHg and torr are identical units.
These conversions are essential for gas law problems, especially when using the Ideal Gas Law (PV = nRT) where R = 0.08206 L·atm/mol·K requires
pressure in atmospheres.
3. Amonton's Law (Gay-Lussac's Law) describes the relationship between:
A. Volume and temperature at constant pressure
B. Pressure and volume at constant temperature
C. PRESSURE and TEMPERATURE at constant volume — P₁/T₁ = P₂/T₂ (direct relationship)
D. Volume and moles at constant temperature and pressure
CORRECT ANSWER C — Amonton's/Gay-Lussac's Law: P ∝ T (direct); P₁/T₁ = P₂/T₂ at constant V and n
RATIONALE Amonton's Law (also called Gay-Lussac's Law): at constant volume, the pressure of a gas is directly proportional to its absolute temperature
(Kelvin). As temperature increases, molecules move faster and collide more forcefully → pressure increases. Example: never heat a sealed
container. Option A is Charles' Law (V ∝ T). Option B is Boyle's Law (P ∝ 1/V). Option D is Avogadro's Law (V ∝ n). All four combine into the Ideal Gas
Law (PV = nRT). Temperature must ALWAYS be in Kelvin for gas laws.
, 4. Convert 0°C to Kelvin.
A. 0 K
B. 273 K — K = °C + 273
C. 100 K
D. 373 K
CORRECT ANSWER B — 273 K; Kelvin = Celsius + 273; 0°C is the freezing point of water = 273 K
RATIONALE The Kelvin scale is the absolute temperature scale. 0 K = absolute zero (all molecular motion theoretically stops). K = °C + 273 (more precisely
+273.15). 0°C = 273 K (freezing point of water), 100°C = 373 K (boiling point), 25°C = 298 K (room temperature). All gas law calculations REQUIRE
Kelvin — using Celsius produces incorrect results because gas laws depend on absolute temperature. This is one of the most common errors on
general chemistry exams.
5. Charles' Law states that:
A. Pressure and volume are inversely proportional
B. Volume and temperature are directly proportional at constant pressure: V₁/T₁ = V₂/T₂
C. Volume and moles are directly proportional
D. Pressure and temperature are directly proportional
CORRECT ANSWER B — Charles' Law: V ∝ T (direct); V₁/T₁ = V₂/T₂ at constant P and n; temperature in Kelvin
RATIONALE Charles' Law (1787): the volume of a gas is directly proportional to its absolute temperature when pressure is held constant. As temperature
increases, gas expands (hot air balloons work on this principle). Temperature MUST be in Kelvin. A graph of V vs. T is linear with an intercept at
absolute zero (-273°C). Option A is Boyle's Law (P₁V₁ = P₂V₂). Option C is Avogadro's Law. Option D is Amonton's/Gay-Lussac's Law. Charles' Law
combines with the other gas laws into the Combined Gas Law and Ideal Gas Law.
6. Boyle's Law states that:
A. Volume and temperature are directly proportional
B. Volume and pressure are INVERSELY proportional at constant temperature: P₁V₁ = P₂V₂
C. Pressure and temperature are directly proportional
D. Volume and moles are directly proportional
CORRECT ANSWER B — Boyle's Law: P ∝ 1/V (inverse); P₁V₁ = P₂V₂ at constant T and n
RATIONALE Boyle's Law (1662): pressure and volume are inversely proportional at constant temperature. As pressure increases, volume decreases
proportionally (and vice versa). This is because gas molecules have more space when pressure is reduced. Example: squeezing a syringe —
decreasing volume increases pressure. P × V = constant. A graph of P vs. 1/V is linear. Boyle's Law is the oldest of the gas laws and is fundamental to
understanding gas behavior. Combined with Charles', Gay-Lussac's, and Avogadro's laws to form the Ideal Gas Law.
7. What is the Ideal Gas Law equation?
A. P₁V₁ = P₂V₂
B. PV = nRT — combines pressure, volume, moles, gas constant, and temperature
C. V₁/T₁ = V₂/T₂
D. P₁/T₁ = P₂/T₂
CORRECT ANSWER B — PV = nRT; R = 0.08206 L·atm/mol·K; this is the fundamental equation relating P, V, n, and T for ideal gases
RATIONALE The Ideal Gas Law combines Boyle's, Charles', Gay-Lussac's, and Avogadro's laws. P = pressure (atm), V = volume (L), n = number of moles, R =
universal gas constant (0.08206 L·atm/mol·K), T = temperature (KELVIN). At STP (0°C, 1 atm), 1 mole of any ideal gas occupies 22.4 L. The equation
can be rearranged to solve for any variable. Density of a gas: ρ = PM/RT (derived from PV = nRT by substituting n = m/M). Real gases deviate from
ideality at high pressure and low temperature due to intermolecular forces and molecular volume.
8. What is the Combined Gas Law?
A. P₁V₁/T₁ = P₂V₂/T₂ — combines Boyle's, Charles', and Gay-Lussac's laws when moles are constant
B. PV = nRT
C. P₁V₁ = P₂V₂
D. V₁/n₁ = V₂/n₂
CORRECT ANSWER A — Combined Gas Law: P₁V₁/T₁ = P₂V₂/T₂; used when P, V, and T all change but moles (n) remain constant
RATIONALE The Combined Gas Law integrates Boyle's (P₁V₁ = P₂V₂), Charles' (V₁/T₁ = V₂/T₂), and Gay-Lussac's (P₁/T₁ = P₂/T₂) into one equation. If one variable is
constant, it cancels out, leaving the individual law. Example: constant T → P₁V₁ = P₂V₂. The Combined Gas Law is used when only P, V, and T change
(n constant). For problems involving moles, use the Ideal Gas Law (PV = nRT). All temperatures must be in Kelvin. This is the most versatile gas law
for "before and after" problems.
9. Dalton's Law of Partial Pressures states that:
A. The pressure of each gas is independent of the others
B. The TOTAL pressure of a gas mixture equals the SUM of the partial pressures of each component gas: Ptotal = P₁ + P₂ + P₃ ...
C. The pressure of a gas is proportional to its molar mass
D. Gases cannot be mixed without changing pressure
CORRECT ANSWER B — Dalton's Law: Ptotal = P₁ + P₂ + P₃ ...; each gas exerts pressure independently as if it occupied the container alone
RATIONALE Dalton's Law: in a mixture of non-reacting gases, the total pressure is the sum of the partial pressures of each component. Each gas behaves
independently. The mole fraction (Xᵢ = nᵢ/ntotal) relates partial pressure to total pressure: Pᵢ = Xᵢ × Ptotal. This is important for collecting gases over
water: Ptotal = Pgas + Pwater (vapor pressure of water must be subtracted). Dalton's Law assumes ideal gas behavior and is based on the kinetic
molecular theory — gas particles have negligible volume and no intermolecular forces.
Portland State University
● ●
PSU Department of Chemistry — CHEM 210 Chapters 8–9
LET KNOWLEDGE SERVE THE CITY
CHEM 210
CHEM 210 — Examination 4 (Chapters 8–9)
GAS LAWS, KINETIC MOLECULAR THEORY, THERMODYNAMICS & CALORIMETRY | 2026/2027
INSTITUTION Portland State University (PSU) COURSE CODE CHEM 210 — Chapters 8–9
PROGRAM Undergraduate Chemistry / Pre-Professional ACADEMIC YEAR
EXAM TITLE Examination 4 — Gases & Thermochemistry TOTAL QUESTIONS 25 Questions
SUBJECT AREAS Gas Laws, KMT, Thermodynamics, Calorimetry, FORMAT Multiple Choice — Select the Single Best Answer
Enthalpy
EXAMINATION INSTRUCTIONS
▸ Select the single best answer for each multiple-choice question.
▸ Topics include: gas laws (Boyle's, Charles', Amonton's/Gay-Lussac's, Avogadro's, Combined, Ideal), kinetic molecular theory, Dalton's law of partial pressures,
Graham's law of effusion, and gas density.
▸ Thermodynamics: first law, enthalpy, calorimetry, Hess's law, standard enthalpy of formation, bond energy, and lattice energy.
▸ Temperature must be in Kelvin for all gas law calculations. Standard pressure = 1 atm = 760 mmHg = 760 torr.
▸ Correct answers and detailed rationales appear below each question for exam review purposes.
SECTION I — GAS LAWS, PRESSURE & KINETIC MOLECULAR THEORY Questions 1 – 14
1. What is the formula for pressure?
A. Force × Area
B. Force / Area
C. Mass / Volume
D. Density × Volume
CORRECT ANSWER B — Pressure = Force / Area; the SI unit is the pascal (Pa) = N/m²
RATIONALE Pressure is defined as force per unit area (P = F/A). In the context of gases, pressure results from molecular collisions with container walls. Standard
atmospheric pressure (1 atm) = 760 mmHg = 760 torr = 101,325 Pa. Hydrostatic pressure is pressure exerted by a fluid due to gravity. Option A is the
inverse (F × A would be force multiplied). Option C (mass/volume) is density. Option D (density × volume) gives mass. Understanding pressure units
and conversions is essential for all gas law calculations.
2. Standard atmospheric pressure (1 atm) supports a column of mercury exactly how high?
A. 100 mm
B. 500 mm
C. 760 mm — 1 atm = 760 mmHg = 760 torr
D. 1000 mm
CORRECT ANSWER C — 760 mmHg = 760 torr = 1 atm; this is the standard atmospheric pressure at sea level
RATIONALE Standard atmospheric pressure was originally defined by Torricelli's mercury barometer — the height of mercury that atmospheric pressure can
support. 1 atm = 760 mmHg = 760 torr (named after Torricelli). This is equivalent to 101.325 kPa or 14.7 psi. The mmHg and torr are identical units.
These conversions are essential for gas law problems, especially when using the Ideal Gas Law (PV = nRT) where R = 0.08206 L·atm/mol·K requires
pressure in atmospheres.
3. Amonton's Law (Gay-Lussac's Law) describes the relationship between:
A. Volume and temperature at constant pressure
B. Pressure and volume at constant temperature
C. PRESSURE and TEMPERATURE at constant volume — P₁/T₁ = P₂/T₂ (direct relationship)
D. Volume and moles at constant temperature and pressure
CORRECT ANSWER C — Amonton's/Gay-Lussac's Law: P ∝ T (direct); P₁/T₁ = P₂/T₂ at constant V and n
RATIONALE Amonton's Law (also called Gay-Lussac's Law): at constant volume, the pressure of a gas is directly proportional to its absolute temperature
(Kelvin). As temperature increases, molecules move faster and collide more forcefully → pressure increases. Example: never heat a sealed
container. Option A is Charles' Law (V ∝ T). Option B is Boyle's Law (P ∝ 1/V). Option D is Avogadro's Law (V ∝ n). All four combine into the Ideal Gas
Law (PV = nRT). Temperature must ALWAYS be in Kelvin for gas laws.
, 4. Convert 0°C to Kelvin.
A. 0 K
B. 273 K — K = °C + 273
C. 100 K
D. 373 K
CORRECT ANSWER B — 273 K; Kelvin = Celsius + 273; 0°C is the freezing point of water = 273 K
RATIONALE The Kelvin scale is the absolute temperature scale. 0 K = absolute zero (all molecular motion theoretically stops). K = °C + 273 (more precisely
+273.15). 0°C = 273 K (freezing point of water), 100°C = 373 K (boiling point), 25°C = 298 K (room temperature). All gas law calculations REQUIRE
Kelvin — using Celsius produces incorrect results because gas laws depend on absolute temperature. This is one of the most common errors on
general chemistry exams.
5. Charles' Law states that:
A. Pressure and volume are inversely proportional
B. Volume and temperature are directly proportional at constant pressure: V₁/T₁ = V₂/T₂
C. Volume and moles are directly proportional
D. Pressure and temperature are directly proportional
CORRECT ANSWER B — Charles' Law: V ∝ T (direct); V₁/T₁ = V₂/T₂ at constant P and n; temperature in Kelvin
RATIONALE Charles' Law (1787): the volume of a gas is directly proportional to its absolute temperature when pressure is held constant. As temperature
increases, gas expands (hot air balloons work on this principle). Temperature MUST be in Kelvin. A graph of V vs. T is linear with an intercept at
absolute zero (-273°C). Option A is Boyle's Law (P₁V₁ = P₂V₂). Option C is Avogadro's Law. Option D is Amonton's/Gay-Lussac's Law. Charles' Law
combines with the other gas laws into the Combined Gas Law and Ideal Gas Law.
6. Boyle's Law states that:
A. Volume and temperature are directly proportional
B. Volume and pressure are INVERSELY proportional at constant temperature: P₁V₁ = P₂V₂
C. Pressure and temperature are directly proportional
D. Volume and moles are directly proportional
CORRECT ANSWER B — Boyle's Law: P ∝ 1/V (inverse); P₁V₁ = P₂V₂ at constant T and n
RATIONALE Boyle's Law (1662): pressure and volume are inversely proportional at constant temperature. As pressure increases, volume decreases
proportionally (and vice versa). This is because gas molecules have more space when pressure is reduced. Example: squeezing a syringe —
decreasing volume increases pressure. P × V = constant. A graph of P vs. 1/V is linear. Boyle's Law is the oldest of the gas laws and is fundamental to
understanding gas behavior. Combined with Charles', Gay-Lussac's, and Avogadro's laws to form the Ideal Gas Law.
7. What is the Ideal Gas Law equation?
A. P₁V₁ = P₂V₂
B. PV = nRT — combines pressure, volume, moles, gas constant, and temperature
C. V₁/T₁ = V₂/T₂
D. P₁/T₁ = P₂/T₂
CORRECT ANSWER B — PV = nRT; R = 0.08206 L·atm/mol·K; this is the fundamental equation relating P, V, n, and T for ideal gases
RATIONALE The Ideal Gas Law combines Boyle's, Charles', Gay-Lussac's, and Avogadro's laws. P = pressure (atm), V = volume (L), n = number of moles, R =
universal gas constant (0.08206 L·atm/mol·K), T = temperature (KELVIN). At STP (0°C, 1 atm), 1 mole of any ideal gas occupies 22.4 L. The equation
can be rearranged to solve for any variable. Density of a gas: ρ = PM/RT (derived from PV = nRT by substituting n = m/M). Real gases deviate from
ideality at high pressure and low temperature due to intermolecular forces and molecular volume.
8. What is the Combined Gas Law?
A. P₁V₁/T₁ = P₂V₂/T₂ — combines Boyle's, Charles', and Gay-Lussac's laws when moles are constant
B. PV = nRT
C. P₁V₁ = P₂V₂
D. V₁/n₁ = V₂/n₂
CORRECT ANSWER A — Combined Gas Law: P₁V₁/T₁ = P₂V₂/T₂; used when P, V, and T all change but moles (n) remain constant
RATIONALE The Combined Gas Law integrates Boyle's (P₁V₁ = P₂V₂), Charles' (V₁/T₁ = V₂/T₂), and Gay-Lussac's (P₁/T₁ = P₂/T₂) into one equation. If one variable is
constant, it cancels out, leaving the individual law. Example: constant T → P₁V₁ = P₂V₂. The Combined Gas Law is used when only P, V, and T change
(n constant). For problems involving moles, use the Ideal Gas Law (PV = nRT). All temperatures must be in Kelvin. This is the most versatile gas law
for "before and after" problems.
9. Dalton's Law of Partial Pressures states that:
A. The pressure of each gas is independent of the others
B. The TOTAL pressure of a gas mixture equals the SUM of the partial pressures of each component gas: Ptotal = P₁ + P₂ + P₃ ...
C. The pressure of a gas is proportional to its molar mass
D. Gases cannot be mixed without changing pressure
CORRECT ANSWER B — Dalton's Law: Ptotal = P₁ + P₂ + P₃ ...; each gas exerts pressure independently as if it occupied the container alone
RATIONALE Dalton's Law: in a mixture of non-reacting gases, the total pressure is the sum of the partial pressures of each component. Each gas behaves
independently. The mole fraction (Xᵢ = nᵢ/ntotal) relates partial pressure to total pressure: Pᵢ = Xᵢ × Ptotal. This is important for collecting gases over
water: Ptotal = Pgas + Pwater (vapor pressure of water must be subtracted). Dalton's Law assumes ideal gas behavior and is based on the kinetic
molecular theory — gas particles have negligible volume and no intermolecular forces.
