Chapter 18 - Rates of Reactions

Question 1

What is a reaction’s rate?

Answer 1

The change in concentration per second.

Question 2

What is rate measured in?

Answer 2

Mol dm^-3 s^-1

Question 3

In a chemical reaction, if A is zero order, what effect would be seen if [A] is doubled?

Answer 3

Reaction rate would not change.

Question 4

In a chemical reaction, if A is first order, what effect would be seen if [A] is doubled?

Answer 4

Reaction rate would double.

Question 5

In a chemical reaction, if A is second order, what effect would be seen if [A] is doubled?

Answer 5

Reaction rate would quadruple.

Question 6

How is the reaction rate at a specific time worked out using a concentration against time graph?

Answer 6

At the set time, draw a tangent to the curve and measure the gradient to get the rate.

Question 7

If there are two reactants, A and B, what would be the rate equation?

Answer 7

rate = k x [A]^m x [B]^n
k - rate constant
m - order of A
n - order of B

Question 8

What is initial rate?

Answer 8

The instantaneous rate at the beginning of an experiment when t=0.

Question 9

In a concentration time graph, and a rate time graph, what would zero order look like?

Answer 9

Concentration time - linear to 0 concentration

Rate time - Horizontal line

Question 10

In a concentration time graph, and a rate time graph, what would first order look like?

Answer 10

Concentration time - curve getting closer to zero

Rate time - Linear proportional

Question 11

In a concentration time graph, and a rate time graph, what would second order look like?

Answer 11

Concentration time - steeper curve

Rate time - proportional to x^2

Question 12

What are the two ways of continuous monitoring when a gas is produced?

Answer 12

Gas collection

Mass loss

Question 13

What is a way of utilising light to monitor rate?

Answer 13

Using a colourimeter.

Measuring the amount of light absorbed by a solution.

Question 14

What is half life?

Answer 14

The time taken for half of a reactant to be used up.

Question 15

In a concentration time graph, how can you deduce whether the reactant is first or second order?

Answer 15

Measure multiple half lives.
If the half life is constant, it is first order.
If the half life is increasing, it is second order.

Question 16

If the rate is only affected by one reactant, which is first order, what is another way of determining the rate constant?

Answer 16

k = ln2 / t(1/2)

Question 17

What is a reaction mechanism?

Answer 17

A series of steps that, together, make up the overall reaction.

Question 18

What is the rate determining step?

Answer 18

The slowest step in the reaction mechanism of a multi-step reaction.

Question 19

Why does temperature affect the rate constant?

Answer 19

Increasing the temperature, increases rate of reaction and thus rate constant.

Question 20

What is the Arrhenius equation?

Answer 20

k = A x e^(-E(a)/RT)
A - pre exponential factor
-E(a)/RT - exponential factor

Question 21

What is the logarithmic form of the Arrhenius equation?

Answer 21

ln|k| = -E(a)/RT + ln|A|

Question 22

What can the log form of the Arrhenius equation be modelled as?

Answer 22

A straight line graph in y=mx + c
ln|k| is y
-E(a)/R is m
1/T is x
ln|A| is c