Chemistry (C5)

Question 1

Which type of reaction releases energy into the surroundings?

Answer 1

Exothermic

Question 2

Which type of reaction absorbs energy from the surroundings?

Answer 2

Endothermic

Question 3

In an exothermic reaction, what has more energy in it? The products or the reactants?

Answer 3

Reactants

Question 4

In an endothermic reaction, what has more energy in it? The products or the reactants?

Answer 4

Products

Question 5

What would happen to the temperature of the surroundings in an exothermic reaction?

Answer 5

Increase

Question 6

What would happen to the temperature of the surroundings in an endothermic reaction?

Answer 6

Decrease

Question 7

Give three examples of endothermic reactions.

Answer 7

Thermal decomposition reactions
Citric acid + sodium hydrogen carbonate
Sports injury packs
Photosynthesis

Question 8

Give three examples of exothermic reactions.

Answer 8

Combustion
Oxidation
Neutralisation
Displacement
Respiration
Self-heating cans
Hand warmers

Question 9

What is the unit for temperature?

Answer 9

Degrees Celsius (oC)

Question 10

Describe how to determine the temperature change of the reaction between hydrochloric acid and sodium hydroxide solutions.

Answer 10

• Put a measured volume of hydrochloric acid and pour into a polystyrene cup with a lid.
• Record the initial temperature using a thermometer.
• Add a measured volume of sodium hydroxide into the beaker and stir, replace lid.
• Record the final temperature of the mixture.
• Calculate the temperature change of the reaction.

Question 11

Define ‘activation energy’.

Answer 11

Minimum amount of energy that particles must collide with to react.

Question 12

What is the substance called that reduces the activation energy required by a reaction?

Answer 12

Catalyst

Question 13

Is energy released when bonds are broken or bonds are made?

Answer 13

Made

Question 14

Is energy absorbed when bonds are broken or bonds are made?

Answer 14

Broken

Question 15

Describe an endothermic reaction in terms of bond making and breaking.

Answer 15

More energy is required to break the bonds than is released when bonds are made.

Question 16

Describe an exothermic reaction in terms of bond making and breaking.

Answer 16

More energy is released when bonds are made than is required to break the bonds.

Question 17

State how to calculate energy change in a reaction.

Answer 17

Overall energy change = sum of energy required to break bonds – sum of energy released making bonds.

Question 18

What type of energy change would an exothermic reaction have?

Answer 18

Negative (energy is released)

Question 19

What type of energy change would an endothermic reaction have?

Answer 19

Positive (energy is taken in)

Question 20

What is an electrolyte?

Answer 20

A liquid that conducts electricity.

Question 21

Explain why sodium chloride solution is a good electrolyte.

Answer 21

It contains positive and negative ions that are free to move and carry their charge.

Question 22

Describe how to make a simple chemical cell.

Answer 22

Connect two pieces of different metals (electrodes) to an electrolyte.

Question 23

Describe how to make a chemical battery.

Answer 23

Connect two or more chemical cells together in series.

Question 24

What two factors affect the potential difference (voltage) produced by a chemical cell/battery?

Answer 24

1. The metals used as electrodes
2. The electrolyte used

Question 25

Which two metals used in a chemical cell would produce the biggest voltage? Why?

Answer 25

Aluminium and copper ## Footnote The bigger the difference in reactivity, the bigger the voltage produced.

Question 26

What is the chemical difference between a rechargeable and non-rechargeable cell?

Answer 26

Renewable cells - chemical reaction reversed by an external electrical current.

Question 27

Non-rechargeable cells/batteries work until…

Answer 27

One of the reactants is used up.

Question 28

Which type of reaction occurs in a rechargeable cell?

Answer 28

Reversible.

Question 29

Which type of battery is more expensive initially? Rechargeable or non-rechargeable?

Answer 29

Rechargeable.

Question 30

Which type of battery is more expensive in the long term?

Answer 30

Non-rechargeable.

Question 31

What is the name of the fuel cell in which hydrogen is oxidised to produce water and energy?

Answer 31

Hydrogen fuel cell.

Question 32

What is the word equation for the reaction taking place in a hydrogen fuel cell?

Answer 32

Hydrogen + oxygen → water.

Question 33

Suggest two advantages of using hydrogen fuel cells over rechargeable batteries.

Answer 33

• The only waste product of hydrogen fuel cells is water. • Keep producing electricity as long as fuel is provided.

Question 34

Suggest two disadvantages of using hydrogen fuel cells over rechargeable batteries.

Answer 34

• They are very expensive. • Difficult to transport and store hydrogen as it is a flammable gas. • Most hydrogen comes from methane in natural gas (fossil fuel).

Question 35

What is the half equation for the reaction at the cathode in a hydrogen fuel cell? Is this oxidation or reduction?

Answer 35

O2 + 4H+ + 4e- → 2H2O ## Footnote Reduction.

Question 36

What is the half equation for the reaction of hydrogen at the anode in a hydrogen fuel cell? Is this oxidation or reduction?

Answer 36

2H2 → 4H+ + 4e- ## Footnote Oxidation.