SC18: Rates of Reaction - Paper 2

Question 1

Explain the practical methods for determining the rate of a given reaction: (3)

Answer 1

• Measuring mass loss on a balance. (1)
• Measuring the volume of a gas produced. (1)
• Measuring a reaction where there is a colour change at the end of the reaction. (1)

Question 2

Explain how reactions occur when particles collide: (1)

Answer 2

When reactants come together the kinetic energy they possess means their particles will collide and some of these collisions will result in chemical bonds being broken and some new bonds being formed. (1)

Question 3

Explain how the following affects the rate of reaction: (10)

• Temperature (3)
• Concentration (3)
• Surface area to volume ratio of a solid (2)
• Pressure (2)

Answer 3

• Temperature: Increasing the temperature increases the rate of reaction. (1) This is because particles speed up and have more energy. (1) They therefore collide more often and more particles have enough energy to react when they collide. (1)
• Concentration: Increasing the concentration of solutions increases the rate of reaction. (1) This is because the reactant particles speed up and have more energy. (1) They therefore collide more often and more particles have enough energy to react when they collide. (1)
• Surface area to volume ratio of a solid: Increasing the surface area to volume ratio, by decreasing the size of solid pieces while keeping the total volume of solid the same increases the rate of reaction. (1) This is because there is more surface for collisions to occur on, so collisions occur more often. (1)
• Pressure: Increasing the pressure of gases increases the rate of reaction. (1) The reactant particles are squeezed closer together so collisions occur more often. (1)

Question 4

Define the term catalyst: (1)

Answer 4

A substance that speeds up the rate of a reaction without itself being used up. (1)

Question 5

Explain what a catalyst does: (1)

Answer 5

It increases the rate of a reaction in terms of activation energy. (1)

Question 6

Define the term enzyme: (1)

Answer 6

A protein produced by living organisms that acts as a catalyst to speed up the rate of a reaction. (1)

Question 7

Explain how an enzyme is used: (1)

Answer 7

They are used in the production of alcoholic drinks. (1)

Question 8

Define the term rate: (1)

Answer 8

How quickly something happens. (1)

Question 9

Define the following terms: (2)

• Reactants (1)
• Products (1)

Answer 9

• Reactants: A substance used up in a chemical reaction. (1)
• Products: A substance formed in a reaction. (1)

Question 10

Define the term variable: (1)

Answer 10

A factor that can change. (1)

Question 11

Define the term activation energy: (1)

Answer 11

The minimum amount of energy needed to start a reaction. (1)

Question 12

Define the following terms: (2)

• Exothermic (1)
• Endothermic (1)

Answer 12

• Exothermic: A type of reaction in which energy is transferred to the surroundings from the reactants. (1)
• Endothermic: A type of reaction in which energy from the surroundings is transferred to the products. (1)

Question 13

Define the term reaction profiles: (1)

Answer 13

A diagram to show how the energy stored in a substance changed during the course of a chemical reaction. (1)

Question 14

Define the term protein: (1)

Answer 14

A polymer made up of amino acids. (1)

Question 15

Define the following terms: (2)

• Active site (1)
• Substrates (1)

Answer 15

• Active site: The space in an enzyme where the substrate fits during an enzyme-catalyzed reaction. (1)
• Substrates: A substance that is changed during a reaction. (1)

Question 16

Define the term denature: (1)

Answer 16

A denatured enzyme is one where the shape of the active site has changed so much that its substrate no longer fits and the reaction can no longer happen. (1)