Reaction Rates

Question 1

What is meant by rate of reaction?

Answer 1

The rate of a chemical reaction measures how fast a reactant is being used up or how fast a product is being formed.

Question 2

Describe the concentration-time graph for a reaction at different times in the reaction.

Answer 2

The rate of concentration is fastest at the start of the reaction, as each reactant is at its highest concentration.

The rate of reaction slows down as the reaction proceeds, because the reactants are being used up and their concentrations decrease.

Once one of the reactants has been completely used up. the concentration stops changing and the rate of reaction is zero.

Question 3

What are the factors which change the rate of reaction?

Answer 3

Concentration
Temperature
Catalyst
Surface Area

Question 4

Why are some collisions successful and some unsuccessful?

Answer 4

A collision is successful if the particles collide with the correct orientation and sufficient energy to overcome the activation energy.

Question 5

What happens to the ROR when concentration increases?

Answer 5

Increase in concentration, increases the number of particles in that volume. Particles are closer together and will collide more frequently. Therefore, in a given time there will be more successful collisions and an increased ROR.

Question 6

What happens to ROR when pressure is increased?

Answer 6

When a gas is compressed into a smaller volume the pressure of a gas is increased and the ROR is increased.
When there is the same number of gas molecules occupying a smaller space, the concentration of the gas molecules would increase as well.
Gas molecules closer together and collide more frequently, leading to more successful collisions in the same time.

Question 7

What methods could you use to determine the rate of reaction?

Answer 7

Monitoring the volume of gas produced at regular time intervals using gas collection.
Monitoring the loss of mass of reactants using a balance.

For the mass, plot a graph of mass loss against time.
Draw a tangent at t=0 and work out gradient.

For the gas, plot a graph of gas produced against time.
Draw a tangent at t=0 and get gradient.
This is Initial Rate