Module 5.1 - Rates, Equilibrium and pH

Question 1

What is the equation for the rate of reaction?

Answer 1

change in conc of reactant/product

time

Question 2

What is the rate of reaction usually measured in?

Answer 2

mol dm^-3 s^-1 (slower reactions: mol dm^-3 min^-1, difficult to measure conc may be cm³ s^-1)

Question 3

If a reactant has order zero how does it affect the rate of the reaction?

Answer 3

• has no effect
• rate ∝ [A]⁰

Question 4

If a reactant has first order how does it affect the rate of the reaction?

Answer 4

• increasing [reactant] by x increases rate by x
• rate is directly proportional to conc of reactant
• rate ∝ [B]

Question 5

If a reactant has second order how does this affect the rate of reaction?

Answer 5

• change in rate will be equal to change in conc squared
• increasing [reactant] by x increases rate by x²
• rate ∝ [C]²

Question 6

How do you work out the overall order of a reaction?

Answer 6

Sum of individual orders (ie sum of all the powers in the rate equation)

Question 7

What are the units for k in a zero order reaction?

Answer 7

rate = k[A]⁰ ∴ k=rate/1 ∴ units = mol dm^-3 s^-1

Question 8

What are the units for k in a first order reaction?

Answer 8

rate = k[A] ∴ k = rate/[A] ∴ units: s^-1

Question 9

What are the units for k in a second order reaction?

Answer 9

rate = k[A]² ∴ k = rate/[A]² ∴ units = dm³ mol^-1 s^-1

Question 10

What are the units for k in a third order reaction?

Answer 10

rate = k[A]²[B] ∴ k = rate/([A]²[B]) ∴ units = dm⁶ mol^-2 s^-1

Question 11

What is the rate of a reaction?

Answer 11

The change in concentration of a reactant or product per unit time

Question 12

What is the half life of a reactant?

Answer 12

The time taken for the conc of the reactant to reduce by half