Topic 16: Kinetics II

Question 1

What mathematical expression links the rate of reaction to the concentrations of reactants?

Answer 1

Rate equation

The general form is Rate = k[A]^m[B]ⁿ.

Question 2

What does the order of reaction with respect to a reactant describe?

Answer 2

Power of concentration in rate equation

It shows how strongly the rate depends on that reactant’s concentration.

Question 3

Fill in the blank:

In the rate equation Rate = k[A]^m[B]ⁿ, the symbol k represents the rate _______.

Answer 3

constant

The value of k depends on temperature.

Question 4

True or False:

The orders of reaction in A-level chemistry are restricted to values of 0, 1, or 2.

Answer 4

True

Higher or fractional orders are not required for this specification.

Question 5

What name is given to the sum of the powers of the concentrations in a rate equation?

Answer 5

Overall order

For example, if m = 1 and n = 1, the overall order is 2.

Question 6

True or False:

The rate constant k changes when the concentration of reactants changes.

Answer 6

False

k only changes with temperature, not with concentration.

Question 7

Fill in the blank:

The equation k = Ae^-E_a/RT is known as the _______ equation.

Answer 7

Arrhenius

It relates the rate constant to temperature and activation energy.

Question 8

What does the symbol E_a represent in the Arrhenius equation?

Answer 8

Activation energy

It is the minimum energy required for a successful collision.

Question 9

True or False:

Increasing temperature increases the value of the rate constant k.

Answer 9

True

Higher temperature means a larger fraction of molecules exceed activation energy.

Question 10

What must the temperature be measured in when using the Arrhenius equation?

Answer 10

kelvin

Temperature must be converted from °C to K.

Question 11

Fill in the blank:

Rearranging the Arrhenius equation gives ln k = −E_a/RT + ln _______.

Answer 11

A

A is the Arrhenius constant (frequency factor).

Question 12

What is the gradient of a graph of ln k against 1/T?

Answer 12

−E_a/R

This allows activation energy to be calculated experimentally.

Question 13

How is the rate equation for a reaction determined?

Answer 13

Experimentally

It cannot be deduced from the balanced equation and must be determined using experimental data.

Question 14

What does the order of reaction with respect to a reactant indicate about the reaction?

Answer 14

Dependence of rate on concentration

It shows how changing that reactant’s concentration affects reaction rate.

Question 15

Fill in the blank:

The rate at the very start of a reaction is called the _______ rate.

Answer 15

initial

It is measured before significant changes in concentration occur.

Question 16

True or False:

A concentration–time graph can be used to determine the rate of reaction at a specific time.

Answer 16

True

The rate at a point is given by the gradient of a tangent drawn to the curve.

Question 17

What graphical feature represents the rate of reaction on a concentration–time graph?

Answer 17

Gradient

A steeper gradient indicates a faster rate.

Question 18

True or False:

In a zero-order reaction, the rate depends directly on the concentration of the reactant.

Answer 18

False

In zero order reactions, the rate is independent of reactant concentration.

Question 19

Fill in the blank:

If doubling the concentration of a reactant doubles the rate, the reaction is _______ order with respect to that reactant.

Answer 19

first

Rate ∝ [A]¹.

Question 20

If doubling the concentration of a reactant increases the rate fourfold, what is the order with respect to that reactant?

Answer 20

Second

Rate ∝ [A]².

Question 21

True or False:

The orders of reaction can provide information about the rate-determining step of a mechanism.

Answer 21

True

The rate-determining step often reflects the observed rate equation.

Question 22

What type of experiment measures how reaction rate changes with different starting concentrations?

Answer 22

Initial rate method

Rates are measured at the start for different initial concentrations.

Question 23

Fill in the blanks:

The slowest step in a reaction mechanism is called the _______-_______ _______.

Answer 23

rate-determining step

This step controls the overall reaction rate.

Question 24

What experimental method involves tracking concentration changes continuously during a reaction?

Answer 24

Continuous monitoring method

Examples include measuring gas volume, colour change, or pH over time.