5.6 The Rate and Extent of Chemical Changes

Question 1

Activation energy

Answer 1

The minimum amount of energy that particles must collide with to react

Question 2

Catalyst

Answer 2

Catalysts increase the rate of reaction by providing a different pathway for the reaction that has a lower activation energy.

They are not used up during the reaction

Question 3

Collision theory

Answer 3

According to this theory, chemical reactions can occur only when reacting particles collide with each other and with sufficient energy

Question 4

Effect of concentration on reaction rate

Answer 4

Increasing the concentration of reactants in solution means the reacting particles will be closer together

This means they will collide more often so there will be a higher rate of successful collisions and a faster rate of reaction

Question 5

Effect of pressure on reaction rate

Answer 5

Increasing the pressure of gaseous reactants means the reacting particles will be closer together.

This means they will collide more often so there will be a higher rate of successful collisions and a faster rate of reaction

Question 6

Effect of surface area on reaction rate

Answer 6

Increasing the surface area of the reactants means there are more exposed reacting particles.

This means there are more frequent successful collisions so the rate of reaction increases

Question 7

Effect of temperature on reaction rate

Answer 7

Increasing the temperature means the particles will have more kinetic energy and so will move faster.

If the molecules are moving faster they will collide more often and, since they’ve gained kinetic energy, a larger proportion of the particles will have at least the activation energy.

For both these reasons the rate of reaction increases.

Question 8

Equilibrium

Answer 8

When a reversible reaction occurs in apparatus which prevents the escape of reactants and products, equilibrium is reached when the forward and reverse reactions occur at exactly the same rate

Question 9

Rate of reaction

Answer 9

The measure of the amount of product formed or reactant used over time

The units of rate of reaction may be given as g/s or cm³ /s

Question 10

Reversible reaction

Answer 10

Reactions in which the products from the reaction can react together to form the original reactants.

The direction of reversible reactions can be changed by changing
the condition