2. Gases, Kinetics, and Chemical Equilibrium

Question 1

Activation Energy

Answer 1

KE of the coliding molecules must reach this threshold energy for products to occur.

Question 2

Average Translational Kinetic Energy and the Temperature of a Gas

Answer 2

Keavg = (3/2)RT

Question 3

Catalyst

Answer 3

Increases the rate of both FORWARD and REVERSE rxn by lowering Ea. It does not change the equilibrium conditions. It gets the rxn to equilibrium more quickly. It is not consumed and not altered.

Question 4

Chemical Equilibrium

Answer 4

When the forward rxn rate equals the reverse rxn rate. There is no change in concentration of reactants or products. Point of greatest entropy.

Question 5

Collision Model

Answer 5

the rate is proportional to the number of collisions of reactant molecules.

Question 6

Dalton’s Law

Answer 6

Ptotal = P1 + P2 + P3_

Question 7

Dalton’s Law Definition

Answer 7

Total pressure is the sum of the partial pressures.

Question 8

Deviations from Ideal Gas Law (Volume and Pressure)

Answer 8

Volume of Gases (Vreal > Videal); Pressure of Gases (Preal < Pideal)

Question 9

Diffusion

Answer 9

Spreading of one gas into another gas or into empty space.

Question 10

Effusion

Answer 10

effusion rate1/effusion rate2 = squareroot (M2/M1)

Question 11

Effusion Definition

Answer 11

Spreading of a gas from high pressure to very low pressure through a pinhole.

Question 12

Equilibrium Constant K

Answer 12

When you set k of forward reaction equal to k of reverse reaction, get the Law of Mass Action equation.

Question 13

Graham’s Law

Answer 13

v1/v2 = squaroot(m2/m1)

Question 14

Graham’s Law Definition

Answer 14

Relationship of KE of two gases and their rms velocities.

Question 15

Heterogeneous Catalyst

Answer 15

It is in a DIFFERENT phase than the reactants and products. Usually solids.

Question 16

Homogeneous Catalyst

Answer 16

It is in the SAME phase as the reactants and products. Usually in gas or liquid phase.

Question 17

Ideal Gas

Answer 17

These characteristics are not true for real gas. 1) Gas molecules have 0 volume. 2) Gas molecules exert no forces other than repulsive forces due to collisions. 3) Gas molecules make completely elastic collisions. 4) KE avg of gas molecules is directly proportional to the temperature of the gas.

Question 18

Ideal Gas Law

Answer 18

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

Question 19

Intermediates

Answer 19

Species that are products of one reaction and reactants of a later reaction in a rxn change.

Question 20

Kinetic Molecular Theory

Answer 20

Model of an ideal gas, which lacks certain real gas characteristics.

Question 21

Le Chatelier’s Principle

Answer 21

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

Question 22

Mean Free Path

Answer 22

Distance traveled by a gas molecule between collisions.

Question 23

Order of Each Respective Reactant

Answer 23

1st order, 2nd order. Part of the rate law, determined experimentally.

Question 24

Overall Order

Answer 24

When you add all the respective reactant together.

Question 25

Partial Pressure

Answer 25

Pa = XaPtotal (X is the mole fraction of the gas. Mole fraction is moles of gas divided by total number of moles)

Question 26

Partial Pressure Definition

Answer 26

The amount of pressure contributed by any gas in a gaseous mixture is called the partial pressure of that gas.

Question 27

Rate Determining Step

Answer 27

The slowest elementary step determines the rate of the overall rxn. Elementary steps make up the reaction.

Question 28

Rate Law

Answer 28

rate forward = kf[A]^a[B]^b (only an example!)

Question 29

Rate Law Definition

Answer 29

Describes the progress of a rxn. Must be determined experimentally.

Question 30

Reaction Quotient

Answer 30

Using the same equation as K, can predict the direction in which a rxn will proceed. Q = K (equilibrium). Q > K, moves left increases reactants. Q < K, moves right increases products.

Question 31

Standard Molar Volume

Answer 31

22.4 L

Question 32

Standard Temperature and Pressure (STP)

Answer 32

0C, 1atm

Question 33

The Law of Mass Action

Answer 33

K = products^coef/reactants^coef

Question 34

The Reaction Quotient

Answer 34

Q = products^coef/reactants^coef

Question 35

Charles’ Law

Answer 35

volume of a gas is proportional to temperature at constant pressure.

Question 36

Boyle’s Law

Answer 36

volume of a gas is inversely proportional to pressure at constant temperature.

Question 37

Avogadro’s Law

Answer 37

volume of a gas is proportional to the number of moles at constant temp and pressure.

Question 38

What are the two requirements for a reaction to produce products?

Answer 38

1) Enough energy, past activation energy. 2) proper orientation.

Question 39

Rate of a reaction INCREASES/DECREASES with temperature?

Answer 39

INCREASES because more collisions with sufficient relative KE occur each second.

Question 40

Zero Order Reaction

Answer 40

Plot [A] vs. t gives slope -k. The slope is CONSTANT, so the rate constant is constant.

Question 41

First Order Reaction

Answer 41

Plot ln[A] vs. t gives slope -k. Has constant half life independent of [A].

Question 42

Second Order Reaction

Answer 42

Plot 1/[A] vs. t gives slope k. Half life is dependent on [A]. Each consecutive half-life is twice as long as the last.

Question 43

Third Order Reaction

Answer 43

Plot 1(2[A]^2) vs. t gives slope k.

Question 44

Le Chatelier when increase pressure

Answer 44

Equilibrium shifts to the lesser moles.