C5.2 - Controlling Reactions

Question 1

What is rate of reaction a measure of?

Answer 1

The rate of reaction is a measure of how quickly reactants are used or products are formed.

Question 2

What are the two equations to calculate the rate of reaction?

Answer 2

Rate of reaction = Amount of reactant used / Time taken

Rate of reaction = Amount of product formed / Time taken

Question 3

What are two methods of measuring the volume of gas produced in a reaction?

Answer 3

1. Using a gas syringe
   - Has graduations marked in cm3.
   - As the syringe fills, the plunger moves
   outwards.
   - You can then record the volume of gas it
   contains and calculate the rate of reaction.
2. Upside down measuring cylinder in water
   - Gas produced displaces the water in the
   cylinder.
   - However it is not really reliable considering some
   gases like carbon dioxide dissolve in water.

Question 4

How do you calculate the mean rate of reaction between two points?

Answer 4

Rate of reaction = Gradient = Change in volume/Change in time

Question 5

How do you calculate an instantaneous rate of reaction (the rate of reaction at a particular time)?

Answer 5

• Draw a tangent to the point.
• Work out the gradient of the tangent which is the
  instantaneous rate of reaction.

Question 6

What needs to happen for a reaction to happen?

Answer 6

A reaction can only happen if reactant particles collide with each other and the colliding particles have enough energy to react.

Question 7

How does temperature affect the rate of reaction?

Answer 7

As the temperature of a reaction mixture increases:

• The particles move more quickly resulting in
  more frequent collisions.
• A greater proportion of the colliding particles
  have the activation energy of more.
• There is a greater rate of successful collisions.
• There is a greater rate of reaction.

Question 8

What is the relationship between reaction time and rate of reaction?

Answer 8

The rate of reaction is inversely proportional to the reaction time.

Question 9

How does concentration/pressure affect the rate of reaction?

Answer 9

• An increase in concentration/pressure results in
  the particles becoming more crowded.
• This means that there are more frequent collisions
  (a higher rate of collisions).
• This means that rate of successful collisions
  also increases (because the rate of collisions
  increases).
• There is an increased rate of reaction

Question 10

What will the amount of product formed be directly proportional to?

Answer 10

The limiting reactant.

Question 11

How does surface area increase the rate of reaction?

Answer 11

• Only particles at the surface can take part in
  collisions.
• As the surface area increases, the are more
  reactant particles are available for collisions.
• There are therefore more frequent collisions.
• There is a higher rate of successful collisions
  because the rate of collisions is higher.
• This means there is a higher rate of reaction.

Question 12

How do catalysts affect the rate of reaction?

Answer 12

• Catalysts provide an alternative reaction pathway
  with a lower activation energy.
• A greater proportion of the colliding particles have
  the activation energy or more.
• The rate of successful collisions therefore
  increases.