MCAT General Chemistry complete with
Questions and correct Answers
STP - correct answer-✅0°C and 1 atm
Ideal Gas Law - correct answer-✅PV = nRT
At STP, 1 mol of gas will occupy ... - correct answer-✅22.4 L
Characteristics of an Ideal Gas - correct 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) - correct 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) - correct 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 - correct answer-✅Spreading of one gas into another gas or into empty space. Approximated
by Graham's Law.
Graham's law (diffusion) - correct answer-✅
Effusion - correct answer-✅Spreading of a gas from high pressure to very low pressure through a
"pinhole."
Graham's law (effusion) - correct answer-✅Where rates are effusion rates, and Ms are the molar
masses of the gases.
When do "real" gases deviate from ideal gas behavior? - correct 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? - correct answer-✅V(real) > V(ideal)
How does Pressure compare for real and ideal gases? - correct 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? - correct answer-✅- Positive deviation cause: molecular
volume
- Negative deviation cause: attractive intramolecular forces
Kinetics vs. Thermodynamics - correct 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: -
correct 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 - correct answer-✅Rate increases with temperature increase
because more collisions with adequate kinetic energy occur each second.
Factors affecting rate of reaction - correct answer-✅1. Temperature
, 2. Pressure
3. Concentration of certain substances
Rate Law (fwd) - correct 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? - correct 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? - correct 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? - correct answer-✅Plot: ln[A] vs. time
Shape: straight line
slope = -k
Second order rxn graph - correct answer-✅Plot: 1/[A] vs. time
Shape: straight line
slope = +k
Third order rxn graph - correct answer-✅Plot: 1/(2[A]²)
Shape: straight line
slope: +k
Catalyst - correct answer-✅Lowers activation energy and thereby increases reaction rate, but does NOT
alter equilibrium constant
Heterogeneous catalyst - correct answer-✅In a different phase than the reactants and products
Homogeneous catalyst - correct answer-✅In the same phase as the reactants and products
Chemical equilibrium: definition - correct answer-✅Forward and reverse reaction rates are equal.
(Note: NET reaction rate is zero, but there is still a fwd and a rev rxn rate!)
Equilibrium constant equation
(aka the law of mass action) - correct answer-✅Used to study reactions at equilirbium.
K = equilibrium constant; C, D = products; A, B = reactants; and all lowercase letters (a, b, c, d) =
coefficients from balanced chemical equation.
Notes: K is dimensionless, and depends on T. Do NOT use pure liquids (i.e., water) or solids in this
equation!
Reaction quotient equation - correct answer-✅Used to study reactions NOT at equilibrium.
Q = reaction quotient; C, D = products; A, B = reactants; and all lowercase letters (a, b, c, d) = coefficients
from balanced chemical equation.
When Q = K ... - correct answer-✅The chemical reaction is at equilibrium.
When Q > K ... - correct answer-✅The ratio of product:reactant is greater than at equilibrium, so the
reaction will shift left to form more reactants.
When Q < K ... - correct answer-✅The ratio of product:reactant is less than at equilibrium, so the
reaction will shift right to form more products.
Le Chatelier's Principle
(and the conditions where it applies) - correct answer-✅When a system at equilibrium is stressed, the
system will shift in a direction to reduce the stress.
Questions and correct Answers
STP - correct answer-✅0°C and 1 atm
Ideal Gas Law - correct answer-✅PV = nRT
At STP, 1 mol of gas will occupy ... - correct answer-✅22.4 L
Characteristics of an Ideal Gas - correct 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) - correct 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) - correct 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 - correct answer-✅Spreading of one gas into another gas or into empty space. Approximated
by Graham's Law.
Graham's law (diffusion) - correct answer-✅
Effusion - correct answer-✅Spreading of a gas from high pressure to very low pressure through a
"pinhole."
Graham's law (effusion) - correct answer-✅Where rates are effusion rates, and Ms are the molar
masses of the gases.
When do "real" gases deviate from ideal gas behavior? - correct 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? - correct answer-✅V(real) > V(ideal)
How does Pressure compare for real and ideal gases? - correct 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? - correct answer-✅- Positive deviation cause: molecular
volume
- Negative deviation cause: attractive intramolecular forces
Kinetics vs. Thermodynamics - correct 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: -
correct 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 - correct answer-✅Rate increases with temperature increase
because more collisions with adequate kinetic energy occur each second.
Factors affecting rate of reaction - correct answer-✅1. Temperature
, 2. Pressure
3. Concentration of certain substances
Rate Law (fwd) - correct 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? - correct 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? - correct 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? - correct answer-✅Plot: ln[A] vs. time
Shape: straight line
slope = -k
Second order rxn graph - correct answer-✅Plot: 1/[A] vs. time
Shape: straight line
slope = +k
Third order rxn graph - correct answer-✅Plot: 1/(2[A]²)
Shape: straight line
slope: +k
Catalyst - correct answer-✅Lowers activation energy and thereby increases reaction rate, but does NOT
alter equilibrium constant
Heterogeneous catalyst - correct answer-✅In a different phase than the reactants and products
Homogeneous catalyst - correct answer-✅In the same phase as the reactants and products
Chemical equilibrium: definition - correct answer-✅Forward and reverse reaction rates are equal.
(Note: NET reaction rate is zero, but there is still a fwd and a rev rxn rate!)
Equilibrium constant equation
(aka the law of mass action) - correct answer-✅Used to study reactions at equilirbium.
K = equilibrium constant; C, D = products; A, B = reactants; and all lowercase letters (a, b, c, d) =
coefficients from balanced chemical equation.
Notes: K is dimensionless, and depends on T. Do NOT use pure liquids (i.e., water) or solids in this
equation!
Reaction quotient equation - correct answer-✅Used to study reactions NOT at equilibrium.
Q = reaction quotient; C, D = products; A, B = reactants; and all lowercase letters (a, b, c, d) = coefficients
from balanced chemical equation.
When Q = K ... - correct answer-✅The chemical reaction is at equilibrium.
When Q > K ... - correct answer-✅The ratio of product:reactant is greater than at equilibrium, so the
reaction will shift left to form more reactants.
When Q < K ... - correct answer-✅The ratio of product:reactant is less than at equilibrium, so the
reaction will shift right to form more products.
Le Chatelier's Principle
(and the conditions where it applies) - correct answer-✅When a system at equilibrium is stressed, the
system will shift in a direction to reduce the stress.
