Half-lives 118-119

Question 1

Define half-life (of a reactant).

Answer 1

The half-life of a reactant is the time taken for the concentration of the reactant to reduce by half.

Question 2

How is a first-order reaction identified on a concetration-time graph?

Answer 2

• A first-order reaction has a constant half-life.
• The half-life is the same no matter what the concentration is.

Question 3

What is exponential decay?

Answer 3

Process that have a constant half-life, with a value halving every half-life. This is called exponential decay.

Question 4

Draw the concetration-time graph of a zero order reaction.

Answer 4

• Concetration decreases at a constant rate.
• Half-life decreases with time

Question 5

Draw the concentration-time graph for a first order reaction.

Answer 5

• The concentration halves in equal time intervals.
• Half-life is constant.

Question 6

Draw the concentration-time graph for a second order reaction.

Answer 6

Concentration decreases rapidly, but the rate of decrease then slows down.

Half-life increases with time.