[3.1.9] Rate Equations

Question 1

For the following reaction aA + bB -> products, what is the rate equation?

What are each of the components of the equation and their units?

Answer 1

• r = k[A]ᵐ[B]ⁿ.
  
  • k is called the rate constant -> units must be worked out from the equation.
  • The unit of r is usually mol dm⁻³ s⁻¹.
  • The square brackets [A] means the concentration of [A] measured in mol dm⁻³.
  • ᵐ & ⁿ are reaction orders.

Question 2

What reaction orders are there? What do they mean in relation to the concentration of reactant [A]? Draw a graph to represent them.

Answer 2

• Orders are usually integers 0,1,2.
  
  • 0 means the reaction is zero order with respect to that reactant.
  • 1 means first order.
  • 2 means second order.
• For zero order: the concentration of A has no effect on the rate of reaction -> r=k[A]⁰
• For first order: the rate of reaction is directly proportional to the concentration of A -> r=k[A]¹
• For second order: the rate of reaction is proportional to the concentration of A squared -> r=k[A]²

Question 3

How do you calculate the total order for a reaction?

Answer 3

• By adding all the individual orders together.

Question 4

What is the unit of the rate constant if the reaction has a total order of:

• 1
• 2
• 3

Answer 4

Question 5

What is the effect of increasing temperature on the rate constant?

Answer 5

• The rate constant (K) increases when temperature increases.

Question 6

Write the rate equation for the reaction between A and B where A is 1st order and B is 0 order. Calculate the units of K.

Answer 6

Question 7

Write the rate equation for the reaction between A and B where A is 1st order and B is 2nd order. Calculate the units of K.

Answer 7

Question 8

Answer 8

Question 9

Answer 9

Question 10

Calculate the rate constant using the initial rate data below:

Answer 10

Question 11

What is the Arrhenius equation? What are the units of its components?

Answer 11

Question 12

Rearrange the Arrhenius equation to calculate the Arrhenius constant.

Answer 12

Question 13

Rearrange the Arrhenius equation to calculate the activation energy.

Answer 13

Ea = (ln A - In K) x RT

Question 14

Rearrange the Arrhenius equation to calculate the temperature.

Answer 14

T = Ea / (ln A - ln k) x R

Question 15

Answer 15

Question 16

Answer 16

Question 17

Calculate the activation energy using the experimental data and the graph below.

Answer 17