Chapter 5.3 Catalyst

Question 1

Explain why the catalyst is more effective when coated onto an unreactive honeycomb.

Answer 1

• Increase in surface area,

- rate of successive collisions increase

Question 2

Explain why a small increase in temperature has a large effect on the initial rate of a reaction.

Answer 2

There is a small increase in temperature results in collisions with energy greater than the activation energy

Question 3

What is the effect of an increase in temperature on the rate of a chemical reaction?
Explain your answer with reference to the Maxwell–Boltzmann distribution.
Effect
Explanation. (2)

Answer 3

Effect - rate of reaction increases

Explanation - more particles have activation energy

Question 4

What is the effect of the addition of a catalyst on the rate of a chemical reaction?
Explain your answer with reference to the Maxwell–Boltzmann distribution.
Effect
Explanation

Answer 4

Effect - rate of reaction increases,

Explanation - lowers the activation energy so that more molecules are able to react

Question 5

Give one reason why the reaction between hydrogen and chlorine is very slow at room temperature. (1)

Answer 5

-activation energy is high, very few particles have the energy to react

Question 6

Explain why an increase in pressure, at constant temperature, increases the rate of reaction between hydrogen and chlorine

Answer 6

• more particles In a given volume

- therefore more collision

Question 7

Explain why a small increase in temperature can lead to a large increase in the rate of reaction between hydrogen and chlorine

Answer 7

Many more molecules have energy greater than the activation energy

Question 8

Give the meaning of the term catalyst

Answer 8

Speeds up a reaction but is chemically unchanged

Question 9

Suggest one reason why a solid catalyst for a gas-phase reaction is often in the form of a powder

Answer 9

increases the surface area

Question 10

The rate of a chemical reaction may be increased by an increase in reactant concentration, by an increase in temperature and by the addition of a catalyst.

State which, if any, of these changes involves a different activation energy. Explain your answer
Change
Explanation (4)

Answer 10

Change = catalyst 
Explanation = with a catalyst being present the activation energy is lowered so more molecules can react

Question 11

State one way in which the collision frequency between particles in a gas can be increased without changing the temperature.

Answer 11

Increase concentration or pressure

Question 12

Explain In general terms how a catalyst works (3)

Answer 12

• lowers the activation energy,
• so more molecules are able to react,
• alternative route

Question 13

equation for the decomposition of hydrogen peroxide is shown below.
2H2O2 = 2H2O + O2
State the measurements you would take in order to investigate the rate of this reaction

Answer 13

-measure volume of gas at regular time intervals

Question 14

State what is meant by the term rate of reaction

Answer 14

Change in concentration of a substance per unit time

Question 15

Give two reasons, other than an increase in the reaction rate, why these equations suggest that hydrogen bromide is behaving as a catalyst

Answer 15

• remains unchanged ,

- alternative route

Question 16

Magnesium ribbon reacts with hot water. Heated magnesium ribbon reacts with steam. State two differences between these reactions.

Answer 16

• hot water produces the hydroxide,

- steam produced the oxide

Question 17

In terms of collision theory explain why, at a fixed temperature, the rate of this reaction doubles when the concentration of the hydrochloric acid doubles.

Answer 17

• twice the amount of HCL in a given volume,

- twice the amount of successive collisions per unit time

Question 18

Give one reason, other than the increase in rate of reaction, why the student was able to deduce that hydrogen bromide behaves as a catalyst in this two-step reaction

Answer 18

-hydrogen bromide was unchanged at the end of the reaction