Topic 4 - Rates of Reaction

Question 1

What is the rate of reaction?

Answer 1

The rate of reaction is the speed at which reactants change into products.

Question 2

What factors affect the rate of a chemical reaction?

Answer 2

1. The surface area or size of solid particles
2. The concentration of solutions
3. The temperature
4. The presence of a catalyst

Question 3

How can the rate of a chemical reaction be calculated?

Answer 3

Rate = Change in mass of reactant/time taken

Rate = Amount of product produced/time taken

Rate = 1/time taken

Question 4

What is collision theory?

Answer 4

Collision theory states that for a reaction to take place, reacting particles must collide with sufficient energy.

Question 5

What is activation energy?

Answer 5

Activation energy is the minimum energy required for a reaction to take place between reacting particles.

Question 6

What are the two ways of measuring the rate of reaction experimentally?

Answer 6

1. Measuring a change in mass

2. Measuring gas volume produced

Question 7

Name three reactions used in rate of reaction experiments.

Answer 7

1. Metals with dilute acid
2. Marble chips with dilute hydrochloric acid
3. Catalytic decomposition of hydrogen peroxide (Manganese IV Oxide, MnO2)

Question 8

What are the units of rate?

Answer 8

s-1 = 1/s

s= time

Question 9

How can the time for a reaction to be completed be measured for a reaction which produces a gas or in which a solid disappears?

Answer 9

For a reaction that produces a gas, the time for the reaction to finish can be determined by:
• Reading the time when the mass first reaches its minimum on a graph of mass against time.
• Reading the time when the gas volume first reaches its maximum on a graph of gas volume against time.
• Timing the reaction until you see that the production of gas has stopped.

For a reaction in which a solid disappears, the reaction can be timed until no more solid can be seen in the reaction vessel.

Question 10

What is a ‘fair test’?

Answer 10

A ‘fair test’ is the phrase used for an investigation in which one variable is changed (the independent variable), one variable is measured (the dependant variable) and all other variables are kept the same (controlled variables).

Question 11

What is validity?

Answer 11

Suppose an experiment uses two concentrations of acid. The results obtained from this may not be valid because of the limited range of the concentrations. The validity could be improved by using a greater number and range of concentrations of acid.

Question 12

What is reliability?

Answer 12

Reliability depends on whether or not the same result could be obtained again if the experiment were to be repeated.

Question 13

What is an anomaly?

Answer 13

An anomaly is a piece of data that does not match the pattern shown in the rest of the investigation. Many anomalies are easily spotted from a graph - they are indicated by points which do not fall on or close to the line of best fit.

Question 14

What is a catalyst?

Answer 14

A catalyst is a substance which speeds up the rate of reaction without being used up itself.

Question 15

What are the benefits of the development of more effective catalysts?

Answer 15

1. Using less energy
2. Using renewable raw materials
3. Being carried out in fewer steps