MCAT General Chemistry Exam Study Questions
with 100% Correct Trusted Solutions
STP - Answer 0°C and 1 atm
Ideal Gas Law - Answer PV = nRT
At STP, 1 mol of gas will occupy ... - Answer 22.4 L
Characteristics of an Ideal Gas - Answer 1. Gas molecules have zero volume
2. Gas molecules exert no forces other than repulsive forces due to collisions
3. Gas molecules make completely elastic collisions
4. The avg. kinetic energy of gas molecules is directly proportional to the temperature of the gas
Partial pressure of a gas (equation) - Answer Partial pressure equals the mole fraction of the gas
(number of moles of gas "i" divided by total number of moles of gas in sample) times the total pressure.
Average Kinetic Energy (of gas) - Answer KEavg = (3/2)RT
(R = .08206 L atm K⁻¹ mol⁻¹ or 8.314 J K⁻¹ mol⁻¹)
Average kinetic energy applies to ALL gases, regardless of mass.
Diffusion - Answer Spreading of one gas into another gas or into empty space. Approximated by
Graham's Law.
Graham's law (diffusion) - Answer
Effusion - Answer Spreading of a gas from high pressure to very low pressure through a "pinhole."
Graham's law (effusion) - Answer Where rates are effusion rates, and Ms are the molar masses of the
gases.
,When do "real" gases deviate from ideal gas behavior? - Answer When molecules are close together:
- volume becomes significant
- electrostatic forces become significant
- high pressure pushes molecules together
- low temperatures cause gas molecules to settle close together
How does Volume compare for real and ideal gases? - Answer V(real) > V(ideal)
How does Pressure compare for real and ideal gases? - Answer P(real) < P(ideal)
(PV)/(RT) Graph: Real vs. Ideal gas
- What is the cause of POSITIVE deviation?
- What is the cause of NEGATIVE deviation? - Answer - Positive deviation cause: molecular volume
- Negative deviation cause: attractive intramolecular forces
Kinetics vs. Thermodynamics - Answer Kinetics: deals with rate of reaction; how fast equilibrium is
achieved
Thermodynamics: deals with balance of reactants/products after equilibrium reached; what equilibrium
looks like
According to the Collision Model, two conditions must be met for a collision to lead to a reaction: -
Answer 1. Colliding molecules must reach a threshold energy called "activation energy."
2. Colliding molecules must have proper spatial orientation.
Effect of temperature on reaction rate - Answer Rate increases with temperature increase because more
collisions with adequate kinetic energy occur each second.
Factors affecting rate of reaction - Answer 1. Temperature
, 2. Pressure
3. Concentration of certain substances
Rate Law (fwd) - Answer Rate(fwd) = k [A]ⁿ¹[B]ⁿ²
(where n1 and n2 are the order of each respective reactant and n1 + n2 = overall order of reaction)
How do you determine the rate law? - Answer Experimentally - NOT using the coefficients in the
balanced chemical equation!!!
Zero order rxn graph
- what do you plot?
- shape of graph?
- what does slope equal? - Answer Plot: concentration vs. time
Shape: straight line
Slope = -k
First order rxn graph
- what do you plot?
- shape of graph?
- what does slope equal? - Answer Plot: ln[A] vs. time
Shape: straight line
slope = -k
Second order rxn graph - Answer Plot: 1/[A] vs. time
Shape: straight line
slope = +k
Third order rxn graph - Answer Plot: 1/(2[A]²)
with 100% Correct Trusted Solutions
STP - Answer 0°C and 1 atm
Ideal Gas Law - Answer PV = nRT
At STP, 1 mol of gas will occupy ... - Answer 22.4 L
Characteristics of an Ideal Gas - Answer 1. Gas molecules have zero volume
2. Gas molecules exert no forces other than repulsive forces due to collisions
3. Gas molecules make completely elastic collisions
4. The avg. kinetic energy of gas molecules is directly proportional to the temperature of the gas
Partial pressure of a gas (equation) - Answer Partial pressure equals the mole fraction of the gas
(number of moles of gas "i" divided by total number of moles of gas in sample) times the total pressure.
Average Kinetic Energy (of gas) - Answer KEavg = (3/2)RT
(R = .08206 L atm K⁻¹ mol⁻¹ or 8.314 J K⁻¹ mol⁻¹)
Average kinetic energy applies to ALL gases, regardless of mass.
Diffusion - Answer Spreading of one gas into another gas or into empty space. Approximated by
Graham's Law.
Graham's law (diffusion) - Answer
Effusion - Answer Spreading of a gas from high pressure to very low pressure through a "pinhole."
Graham's law (effusion) - Answer Where rates are effusion rates, and Ms are the molar masses of the
gases.
,When do "real" gases deviate from ideal gas behavior? - Answer When molecules are close together:
- volume becomes significant
- electrostatic forces become significant
- high pressure pushes molecules together
- low temperatures cause gas molecules to settle close together
How does Volume compare for real and ideal gases? - Answer V(real) > V(ideal)
How does Pressure compare for real and ideal gases? - Answer P(real) < P(ideal)
(PV)/(RT) Graph: Real vs. Ideal gas
- What is the cause of POSITIVE deviation?
- What is the cause of NEGATIVE deviation? - Answer - Positive deviation cause: molecular volume
- Negative deviation cause: attractive intramolecular forces
Kinetics vs. Thermodynamics - Answer Kinetics: deals with rate of reaction; how fast equilibrium is
achieved
Thermodynamics: deals with balance of reactants/products after equilibrium reached; what equilibrium
looks like
According to the Collision Model, two conditions must be met for a collision to lead to a reaction: -
Answer 1. Colliding molecules must reach a threshold energy called "activation energy."
2. Colliding molecules must have proper spatial orientation.
Effect of temperature on reaction rate - Answer Rate increases with temperature increase because more
collisions with adequate kinetic energy occur each second.
Factors affecting rate of reaction - Answer 1. Temperature
, 2. Pressure
3. Concentration of certain substances
Rate Law (fwd) - Answer Rate(fwd) = k [A]ⁿ¹[B]ⁿ²
(where n1 and n2 are the order of each respective reactant and n1 + n2 = overall order of reaction)
How do you determine the rate law? - Answer Experimentally - NOT using the coefficients in the
balanced chemical equation!!!
Zero order rxn graph
- what do you plot?
- shape of graph?
- what does slope equal? - Answer Plot: concentration vs. time
Shape: straight line
Slope = -k
First order rxn graph
- what do you plot?
- shape of graph?
- what does slope equal? - Answer Plot: ln[A] vs. time
Shape: straight line
slope = -k
Second order rxn graph - Answer Plot: 1/[A] vs. time
Shape: straight line
slope = +k
Third order rxn graph - Answer Plot: 1/(2[A]²)
