Rate equations

Question 1

What is the rate of reaction?

Answer 1

The change in the amount of reactants or products over time.

Question 2

How do you collect a gas produced during a reaction?

Answer 2

A gas syringe

Question 3

How does a colorimeter work?

Answer 3

It measures the absorbance of the solution. The more concentrated a solution is the higher the absorbance.

Question 4

What is the rate equation?

Question 5

What does zero order mean?

Answer 5

If the concentration changes and the rate stays the same.

Question 6

What does first order mean?

Answer 6

The change in the concentration is proportional to the change in the rate.

Question 7

What does second order mean?

Answer 7

The change in the concentration is proportional to the change in the rate squared

Question 8

What effect does an increase in k have on the rate?

Answer 8

The rate increases.

Question 9

What factors affect the size of the rate constant?

Answer 9

The higher the temperature the higher the rate constant.

Question 10

What are the units for rate?

Answer 10

mol dm -3 s-1

Question 11

What is the initial rate?

Answer 11

The rate at the very start of the reaction.

Question 12

How do clock reactions work?

Answer 12

You measure the time taken for a certain product to form as you vary the concentration of one of the reactants.

Question 13

How can you tell when a desired product has been formed?

Answer 13

When there is a colour change.

Question 14

What is the rate-determining step?

Answer 14

The slowest step determines the rate of the reaction.

Question 15

What does the Arrhenius equation show us?

Answer 15

It shows us how the rate constant varies with temperature and activation energy.

Question 16

What effect does an increase in activation energy have on the rate constant k?

Answer 16

The rate constant decreases.

Question 17

What effect does an increase in temperature have on the rate constant k?

Answer 17

The rate constant increases.

Question 18

What is the x-axis and y-axis on an Arrhenius plot?

Answer 18

x = 1/T
y = ln(k)

Question 19

What does the gradient represent on an Arrhenius plot?

Answer 19

• Ea/R

Question 20

How does an iodine clock reaction work?

Answer 20

1. H2O2 + 2H+ + 2I- = I2 + 2H2O
2. 2S2O3 2– + I2 → 2I– + S4O6 2–
3. Most of the iodine from the first reaction will react with the limited sodium thiosulfate but the excess will remain in the solution and react with starch that produces the blue-black colour.
4. The experiment is then repeated with varying concentrations of iodide ions while keeping the concentration of the others the same.