Physical 1 Section 1 - Unit 5: Kinetics

Question 1

State the meaning of the term rate of reaction (1 mark)

Answer 1

• Amount of substance formed per unit of time

Question 2

Explain why, at a fixed temperature, the rate of reaction doubles when the concentration doubles (2 marks)

Answer 2

• Twice as many particles in a set volume

- So twice as many successful collisions

Question 3

Explain the meaning of the term activation energy (2 mark)

Answer 3

• Minimum energy

- For a reaction to start

Question 4

Define the term catalyst and explain how catalysts work (3 marks)

Answer 4

• A substance that speeds up the reaction
• By providing an alternative route
• That has a lower activation energy

Question 5

Explain what must happen for a reaction to occur between molecules of two different gases (2 marks)

Answer 5

• Collision between particles

- With activation energy

Question 6

Explain why a small increase in temperature has a large effect on the initial rate of a reaction (1 mark)

Answer 6

• It increases the frequency of collisions

Question 7

Explain with reference to the Maxwell–Boltzmann distribution what the effect of an increase in temperature is on the rate of a chemical reaction (3 marks)

Answer 7

• Rate of reaction increases
• More molecules
• Have the minimum energy needed to react

Question 8

Explain with reference to the Maxwell–Boltzmann distribution what the effect of the addition of a catalyst is on the rate of a chemical reaction (3 marks)

Answer 8

• Rate of reaction increases
• This lowers activation energy
• So that more molecules are able to react

Question 9

What does the area under a Maxwell- Boltzmann curve represent? (1 mark)

Answer 9

• The number of particles

Question 10

State how, if at all, the value of the most probable energy (Emp) changes as the total number of molecules is increased at constant temperature (1 mark)

Answer 10

• Stays the same

Question 11

State how, if at all, the number of molecules with the most probable energy (Emp) changes as the temperature is decreased without changing the total number of molecules (1 mark)

Answer 11

• Increases

Question 12

State how, if at all, the number of molecules with energy greater than the activation energy (Ea) changes as the temperature is increased without changing the total number of molecules (1 mark)

Answer 12

• Increases

Question 13

Label the X-axis and Y-axis on the Maxwell Boltzmann graph (2 marks)

Answer 13

• X-Axis: Kinetic Energy

- Y-Axis: % of molecules