Chapter 8

Question 1

What is activation energy (Ea) ?

Answer 1

The minimum energy needed to start a reaction

Question 2

What is a catalyst?

Answer 2

A substance that increases the rate of a chemical reaction. It is not used or changed in the reaction. It lowers the activation energy by finding an alternative pathway for the reaction

Question 3

What is collision theory?

Answer 3

An explanation of chemical reactions that says that; particles must collide colliding particles have to have a sufficient amount of energy (Exceed the activation energy) in order for a reaction to take place

Question 4

How can you find the rate of reaction?

Answer 4

Monitor the amount of reactants used up or products produced over time

Question 5

How do you find out the rate of reaction from a graph?

Answer 5

The gradient of a line at any given time The Steeper the gradient the faster the reaction

Question 6

What is rate of reaction given as a formula?

Answer 6

Mean rate of reaction = quantity of reactant used or quantity of product formed / time

Question 7

What effect does surface area have on the rate of reaction?

Answer 7

The rate of reaction increases if the surface area to volume ratio increase. A larger surface area the more chance of a collision

Question 8

What effect does temperature have on the rate of reaction?

Answer 8

Particles collide more frequently and more energetically so more particles have energy that exceeds the activation energy

Question 9

What effect does pressure have on the rate of reaction?

Answer 9

It increases the frequency of collisions as you have a higher number of particles in a given volume

Question 10

What effect does concentration have on the rate of reaction?

Answer 10

It increases the frequency of collisions as you have a higher number of particles in a given volume

Question 11

What is a reversible reaction?

Answer 11

The products of the reaction can react to produce the original reactants

Question 12

What does this show?

Answer 12

A reversible reaction

Question 13

What does dynamic equilibrium mean?

Answer 13

In a closed system the rate of the forward reaction equals the rate of the reverse reaction

Question 14

What is Le Chatelier’s principle?

Answer 14

The rule is that any change made to a reaction which is in equilibrium will result in the equilibrium position moving to minimise the change made

Question 15

What does increasing the temperature do to the position of the equilibrium?

Answer 15

Increasing the temperature always favours the endothermic reaction. Decreasing the temperature always favours the exothermic reaction

Question 16

What does pressure do the position of the equilibrium?

Answer 16

If there is at least one gas present in the equilibrium mixture, then a change in the pressure may affect the position of the equilibrium.

If the pressure increases the equilibrium will shift to the side with the fewest moles of gas.

Changes in pressure will not affect the position of equilibrium if the number of moles of gases on both sides of the equation are equal

Question 17

What effect does a catalyst have on the position of the equilibrium?

Answer 17

A catalyst reduces the time taken to reach equilibrium but does not change the position of the equilibrium. This is because the catalyst increases the rates of the forward and reverse reactions by the same amount

Question 18

Sketch a graph of the effect of concentration on the rate of reaction.

Answer 18

Question 19

In the black cross method for determining the rate of reaction which product forms a precipitate?

Answer 19

The sulfur

HCl + sodium thiosulfate ————-> sodium chloride + sulfur dioxide + sulfur + water.
2HCl(aq) + Na2S2O3(aq) ————> 2NaCl(aq) + SO2(g) + S(s) + H2O(l)

Question 20

Give a method to measure the rate of reaction if a gas is generated?

Answer 20

Use a gas syringe