MCAT General Chemistry Review 2

STP
0oC and 1 atm
Kinetic Molecular Theory

Model of an ideal gas:

-No volume

-No forces (but repulsive due to collisions)

-Completely elastic collision

-Kinetic Energy is directly proportional to temperature

Ideal Gas Law

PV=nRT

(R=0.08206 L atm K-1mol-1 or 8.314J K-1mol-1)

Volume of one mole of an ideal gas at STP
22.4 L
Mole fraction, Χa
Number of moles of gas / total moles of the sample
Partial Pressure, Pa
Pa=XaPtotal
Dalton’s Law
The total pressure exerted by a gaseous mixture is the sum of the partial pressures of each of its gases.
Average translational KE
KE=3/2 RT
Graham’s Law
v1/v2=√m2/√m1
Effusion
Spreading of a gas from high pressure to low pressure through a pinhole.
Diffusion
Spreading of one gas into another gas or into empty space.
Effusion Rate
effusion rate1/effusion rate2 = √M2/√M1
Real gases deviate from Ideal gases at:
High pressure and Low Temperature
Arrhenious Equation for rate constant, k, of a reaction
k=Ae-Ea/RT
Overall Reaction Order
Sum of all the orders of each respective reactant.
Rate determining step
The rate of the slowest elementary step that determines the overall reaction.
Slowest step is the first step

The rate law can be derived directly from this step and no other.

Ex:

1. NO2+NO2–>NO3+NO (slow)

2. NO3+CO–>NO2+CO2 (fast)

rate = k[NO2]2

Slowest step is other than the first step

The slow step is still rate determining but setps prior to the slow step will contribute to the rate determing step.

Ex:

1. NO+Br2–>NOBr2 (fast)

2. NOBr2+NO–>2NOBr (slow)

rate = k[NOBr2][NO]

mass = moles x MW
Equilibrium

Rate of the forward equals the reverse.

This is the point of greatest entropy.

aA+bB–>cC+dD

The Law of Mass Action

K=[C]c[D]d/[A]a[B]b

 

K is the equilibrium constant

Reaction Quotient, Q

Q=[C]c[D]d/[A]a[B]b

Q always changes towards K.

Q = K, Equilibrium

Q>K, leftward shift

Q<K, rightward shift

Le Chatlelier’s Principle

When a system at equilibrium is stressed, the sstem will shift in a direction to reduce the stress.

1)Adding/removing reactants/products

2)Changing the pressure in the system

3) heating/cooling

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