Theories of Chemical Kinetics

Question 1

What does Collision Theory say?

Answer 1

Particles must collide in order to react.

Question 2

What is an effective collision?

Answer 2

A collision in which particles have sufficient energy and correct orientation to react

Question 3

Does an effective collision always lead to a reaction?

Answer 3

Not always

Question 4

If there are 3 particles of reactant A and 2 particles of reactant B, how many possible collisions are there?

Answer 4

6 (2 x 3)

Question 5

What is the orientation probability factor (p) ?

Answer 5

The ratio of effectively-oriented collisions to all possible collisions

Question 6

Does a more complex reactant structure mean a smaller or larger value for orientation probability factor (p) ?

Answer 6

Smaller

Question 7

What is activation energy (Ea)?

Answer 7

The energy needed to convert reactants to an activated, or transition, state. It is an energy threshold colliding molecules must exceed in order to react.

Question 8

What are the units for activation energy (Ea)?

Answer 8

kJ/mol or J/mol

Question 9

Does a higher activation energy (Ea) mean a faster or slower reaction?

Answer 9

Slower because it takes more energy for the reaction to occur

Question 10

Transition State Theory says that an effective collision of particles leads to the formation of what?

Answer 10

A transition state

Question 11

What is a transition state?

Answer 11

An unstable species with partial bonds partway between the reactants and products.

Question 12

The energy to form a transition state is also known as what?

Answer 12

Activation energy (Ea)

Question 13

A transition state exists at the point of maximum
__________________
(fill in the blank)

Answer 13

Potential energy

Question 14

As temperature increases, what happens to the rate constant k?

Answer 14

k increases exponentially

Question 15

Does temperature have a minor or major effect on collision frequency?

Answer 15

Minor effect

Question 16

Does temperature have a minor or major effect on collision energy?

Answer 16

Major effect

Question 17

What is Ea (fwd), the activation energy for a forward reaction?

Answer 17

The energy difference between reactants and the transition state

Question 18

What is Ea (rev), the activation energy for a reverse reaction?

Answer 18

The energy difference between the transition state and the products

Question 19

What formula do you use to find ΔHrxn from Ea(fwd) and Ea(rev)?

Answer 19

ΔHrxn = Ea(fwd) - Ea(rev)

Question 20

In an endothermic reaction, do products or reactants have more energy?

Answer 20

Products

Question 21

In an exothermic reaction, do products or reactants have more energy?

Answer 21

Reactants

Question 22

In an endothermic reaction, which is bigger, Ea(fwd) or Ea(rev)?

Answer 22

Ea(fwd)

Question 23

In an exothermic reaction, which is bigger, Ea(fwd) or Ea(rev)?

Answer 23

Ea(rev)

Question 24

What is the Arrhenius equation?

Answer 24

k = Ae^-Ea/RT
k = rate constant
Ea = activation energy
A = frequency factor
T = temp in K
R = gas constant 8.314 J/mol(K)

Question 25

If you know k at 2 temperatures, what formula do you use to find Ea?

Answer 25

Ea = R(ln (k2/k1))(1/T1 - 1/T2)^-1
R = gas constant 8.314 J/mol(K)

Question 26

How do you find activation energy from the potential energies of the transition state and of the reactants?

Answer 26

Ea = Energy of transition state - energy of reactants