Exam 3 (kinetics and equilibrium)

Question 1

Homogenous vs. heterogenous rxns

Answer 1

homo: all of the species within the reaction are in the same phase

hetero: all the species within the reaction are not in the same phase

Question 2

Are solids and liquids included in the Kc expression? Why?

Answer 2

No; their associated pressure remains the same at a particular temperature

Question 3

How to find Kp given Kc

Answer 3

Kp= Kc [(RT)prod/(RT)react]

*# moles (RT)prod/ # moles (RT)react
*moles are the same, then Kp=Kc

Question 4

How to find Knet:
a. two separate steps
b. reverse direction
c. coefficients multiplied

Answer 4

a. (k1)(k2)= Knet
b. (1/k)
c. K^n ; n=coefficient multiplier

Question 5

Exothermic rxn:
- what will an increase in temp do to a rxn in equilibrium

Answer 5

a. increase temp, shift to the left, less product & more reactant, K will decrease

Question 6

Endothermic reaction:
- what will an increase in temp do to a rxn in equilibrium

Answer 6

a. increase temp, shift to the right, more products & less reactants, k increases

Question 7

How does pressure affect equilibrium?

Answer 7

increasing pressure will shift rxn to the side with less moles

decreasing pressure will shift rxn to the side with more moles

moles on both sides of rxn are equal will mean no change

Question 8

How does concentration affect equilibrium?

Answer 8

increasing concentration will shift rxn in opposite direction
decreasing concentration with shift rxn in the same direction

Question 9

How does ph affect equilibrium?

Answer 9

increasing acid concentration will decrease ph (more acidic)

decreasing acid concentration will increase ph (more basic)

Question 10

How does increasing pressure and decreasing volume affect equilibrium?

Answer 10

will shift to side with less moles;
K is affected.

K will decrease if shifting to reactants
K will increase if shifting to products.

Question 11

How does decreasing pressure and increasing volume affect equilibrium?

Answer 11

will shift to the side with more moles; K is affected.

K will increase if shifting to products side
K will decrease if shifting to reactants side

Question 12

what happens to Q when reactants are added?

Answer 12

Q decreases, so the equilibrium shifts to produce more products

Question 13

what happens to Q when products are added?

Answer 13

Q increases, so the equilibrium shifts to produce more reactants

Question 14

if Q < K, then…

Answer 14

the reaction is not at equilibrium and will make more products at the expense of reactants

Question 15

if Q >K, then…

Answer 15

the reaction is not at equilibrium and will make more reactants at the expense of products

Question 16

A. When K > 1
B. When K < 1
C. When K=1

Answer 16

A. favors products
B. favors reactants
C. is at equilibrium

Question 17

The ways a rate of rxn can be followed are?

Answer 17

Temp, pressure, weight (sedimentation), color and ph

Question 18

What is kinetics

Answer 18

how fast a reaction proceeds and the detailed mechanism involved for each of the step(s) involved as the reaction proceeds from reactants to products

Question 19

How to find average rate?

Answer 19

[final] - [initial] / Tf - Ti

Question 20

Instantaneous rate?

Answer 20

the same as average but is specific to a moment in time

Question 21

When will instantaneous rate be the fastest?

Answer 21

at the beginning of a reaction, when t=0

Question 22

First order equation

Answer 22

ln(At) - ln(Ao) = -kt

At=Ao e^-kt

-kt = slope and ln(Ao)= c

Question 23

First order graph (concentration vs. time)

Answer 23

negative slope

Question 24

second order equation

Answer 24

1/At - 1/Ao = kt
or
1/At= 1/Ao + kt

Question 25

second order graph (concentration vs. time)

Answer 25

Question 26

first order graph (rate vs. concentration)

Answer 26

positive slope

Question 27

second order graph ( rate vs. concentration)

Answer 27

positive slope

Question 28

zero order graph (rate vs. concentration)

Answer 28

Question 29

zero order graph (concentration vs. time )

Answer 29

Question 30

second order graph ( 1/concentration vs. time)

Answer 30

Question 31

zero order equation

Answer 31

[A]= [Ao] - kt

Question 32

temperatures effect on rxn?

Answer 32

higher temp , larger K, faster the rate of rxn

Question 33

frequency of collision/collision frequency affect on rxn?

Answer 33

increase in the frequency of collisions, increases rate of rxn

collision frequency increases with concentration

Question 34

kinetic energy of the collisions/collision energy affect on rxn?

Answer 34

K.E increases with an increase in temp

Question 35

activation energy affect on rxn?

Answer 35

smaller Ea , larger K.e, larger the K, faster the rate

Question 36

what does the collision theory say rate of rxn depends on?

Answer 36

energy of collisions and the orientation of colliding molecules

Question 37

Arrhenius equation

Answer 37

k= Ae^-Ea/RT
lnk2 -lnk1= - Ea/R (1/T2 - 1/T1)

k= rate constant
A= Arrhenius/collision factor
R= Gas constant

• only affected by temp
  A=pZ ; Z= collision frequency, p= ratio of orientated collisions out of all possible collisions

Question 38

what does the Arrhenius equation do?

Answer 38

it accounts for the collision frequency, kinetic energy, orientation, and concentration of molecules in a reaction.