Gases, Kinetics, and Chemical Equilibrium

Question 1

Standard Temperature and Pressure (STP)

Answer 1

0 Celsius, and 1 atm

Question 2

mean free path

Answer 2

distance traveled by a gas molecule between collisions

Question 3

polarity differences and gas…

Answer 3

polarity differences do not cause gases to separate as liquids do

Question 4

temperature differences and gases

Answer 4

temp differences –> gases separate

Question 5

Kinetic Molecular Theory

Answer 5

model of ideal gas

1. gas molecules have zero volume
2. molecules exert no forces other than repulsive forces due to collisions
3. molecules make completely elastic collisions
4. average KE of gas molecules is directly proportional to temp of gas

Question 6

idea gas law

Answer 6

PV = nRT

Question 7

at STP one mole of any ideal gas will occupy…

Answer 7

the standard molar volume of 22.4 liters

Question 8

in mixture of gases, each gas contributes to pressure…

Answer 8

each gas contributes to pressure in same proportion as # of molecules in gas

Question 9

partial pressure

Answer 9

Pa = X*Ptot.
total pressure of mixture * mole fraction
mole fraction = moles of gas a/total moles

Question 10

Dalton’s Law

Answer 10

total pressure exerted by gaseous mixture is sum of partial pressures

Question 11

average translational kinetic energy (KE) for 1 mol of ideal gas =

Answer 11

KE = 3/2RT

Question 12

Graham’s Law

Answer 12

V1/V2 = sqrt(m2)/sqrt(m1)

average speed of molecules of pure gas is inversely proportional to square root of mass of gas molecules

Question 13

effusion

Answer 13

spreading of gas from high pressure to very low pressure through a pinhole
effusion rate 1/effusion rate 2 = sqrt(M2)/sqrt(M1)

Question 14

diffusion

Answer 14

spreading of one gas into another gas or into empty space
- much slower than rms velocity of molecules
(same equation as effusion)

Question 15

Real gases

Answer 15

deviate from ideal behavior when molecules are close together
-from high pressure and cold temps
V real > V ideal
P real < P ideal

Question 16

chemical kinetics vs. thermodynamics

Answer 16

kinetics: how fast equilibrium is achieved
thermodynamics: what equilibrium looks like

Question 17

collision model of reactions

Answer 17

method for visualizing chemical reactions
in order for reaction to occur, reacting molecules must collide
-rate of given reaction is much lower than the frequency of collisions –> all collisions do not result in a reaction

Question 18

2 requirements for a given collision to create a new molecule in a reaction

Answer 18

relative kinetic energies of the colliding molecules must reach the activation energy, colliding molecules must have proper spatial orientation

Question 19

rate of a reaction and temperature

Answer 19

the rate of a reaction increases with temperature

-more collisions with sufficient relative KE occur each second

Question 20

activation energy and temperature

Answer 20

Ea is independent of temperature, activation energy does not change with temperature

Question 21

intermediates

Answer 21

species that are products of one reaction and reactants of a later reaction in a chain

Question 22

rate law for aA + bB –> cC + dD

Answer 22

rate(forward) = k [A]^alpha [B]^beta
k = rate constant
alpha and beta = order of each respective reactant

Question 23

order of each respective reactant

Answer 23

alpha and beta

for elementary reaction: alpha = a and beta = b

Question 24

overall order of reaction

Answer 24

sum or order of each respective reactant

Question 25

determine rate law by experiment

Answer 25

see pages 38-39

Question 26

zero order rate law

Answer 26

plot [A] with respect to time –> straight line with slope of -k

Question 27

first order rate law

Answer 27

[A] decreases exponentially

graph of ln[A] with respect to time –> straight line with slope of -k

Question 28

rate determining step

Answer 28

rate of the slowest elementary step determines overall reaction rate

Question 29

if first step is slow step…

Answer 29

rate law derived directly from this step

Question 30

if slow step is not first….

Answer 30

use equilibrium approximation… page 42

Question 31

catalyst

Answer 31

increases the rate of a reaction without being consumed or permanently altered
creates a new reaction pathway that typically includes an intermediate
-increases rate of forward and reverse reactions
-does not change equilibrium conditions, just gets it there more quickly
-most lower activation energy

Question 32

a catalyst cannot alter the

Answer 32

equilibrium constant of a reaction

Question 33

heterogeneous catalyst

Answer 33

in a different phase than the reactant and products. usually solid while the reactants/products liquids or gases

Question 34

homogenous catalyst

Answer 34

same phase as reactants and products (often aq. acid or base solutions)

Question 35

chemical equilibrium

Answer 35

when forward reaction rate equal reverse reaction rate

• no change in concentration of products and reactants
• net reaction rate is 0, but there is a forward and reverse reaction rate

Question 36

equilibrium is point of greatest ___

Answer 36

greatest entropy

*nature wants to increase entropy

Question 37

Law of Mass Action

Answer 37

for aA + bB –> cC + dD
equilibrium constant K = [C]^c [D]^d / [A]^a [B]^b = products^coefficients/reactants ^coefficients
*good for all equations, not must elementary

Question 38

equilibrium constant, K, depends on..

Answer 38

temperature only

Question 39

don’t use ___ in law of mass action

Answer 39

don’t use solids or pure liquids (water) in law of mass action

Question 40

Q, reaction quotient

Answer 40

same formula as K, equilibrium constant

used to predict direction in which reaction will proceed when not in equilibrium

Question 41

Q > K

Answer 41

more products than reactants, reaction shifts left (increases reactants)
reverse reaction rate greater than forward rate

Question 42

Q < K

Answer 42

more reactant than products, reaction shifts right (increase products)
forward reaction rate greater

Question 43

Le Chatelier’s Principle

Answer 43

when a system at equilibrium is stressed, the system will shift in a direction to reduce that stress