Chapter 14

Question 1

What happens to the rate of a reaction over time?

Answer 1

Generally slows down because concentration of reactants decreases

Question 2

Compare order and order of reaction

Answer 2

Order: exponent of specific reactant

Order of reaction: sum of exponents on reactants

Question 3

Name 4 factors that affect the rate of a reaction

Answer 3

1. Temperature
2. Reactant concentrations
3. Catalyst
4. Physical state

Question 4

What is zero order (n=0)?

Answer 4

Rate of reaction is always the same

Doubling [A] has no effect on reaction rate

Question 5

What is first order (n=1)?

Answer 5

Rate is directly proportional to reactant concentration

Doubling [A] will double reaction rate

Question 6

What is second order (n=2)?

Answer 6

Rate is directly proportional to square of reactant concentration

Doubling [A] will quadruple rate of reaction

Question 7

What is the units, slope and y-intercept of zero-order reactions?

Answer 7

Units: M • s^-1

Slope: -k

y-intercept: [A]₀

Question 8

What is the units, slope and y-intercept of first-order reactions?

Answer 8

Units: s^-1

Slope: -k

y-intercept: ln[A]₀

Question 9

What is the units, slope and y-intercept of second-order reactions?

Answer 9

Units: M^-1 • s^-1

Slope: k

y-intercept: 1/[A]₀

Question 10

For Arrhenius equation, what do A and E_a represent?

Answer 10

A: frequency factor - number of molecules that begin to form activated complex (transition from reactants to products)

E_a: activation energy - minimum energy need to start reaction (difference between reactants and activated complex)

Question 11

What is the activated complex?

Answer 11

Chemical special with partially broken and partially formed bonds (transistion state)

Question 12

If E_a increases, what happens to exponential factor and reaction rate in Arrhenius equation?

Answer 12

Decreases

The higher the energy barrier (larger activation energy), the fewer molecules that have sufficient energy to overcome it.

Question 13

If Temperature increases, what happens to exponential factor and reaction rate in Arrhenius equation?

Answer 13

Increases

Increasing temperature will increase the number of molecules with sufficient energy to overcome the energy barrier.

Question 14

What 2 terms can the frequency factor (A) be broken into?

Answer 14

Orientation factor (p)

Collision frequency (z)

Question 15

What makes a mechanism valid?

Answer 15

1. The elementary steps must sum to the overall reaction.
2. The rate law predicted by the mechanism must
   be consistent with the experimentally observed rate law.

Question 16

What is a catalyst?

Answer 16

A substance that lowers rate of reaction by lowering activation energy without being consumed.

Note: It may be consumed in an early mechanism step then made up at a later step.