Chapter 6

Question 1

Exothermic Reaction

Answer 1

A reaction that gives out energy and is accompanied by a temperature increase. There are bonds formed in an exothermic reaction.

Question 2

Endothermic Reaction

Answer 2

A reaction that takes in energy and is accompanied by a temperature decrease. There are bonds broken in an endothermic reaction.

Question 3

Exothermic Energy Level Diagrams

Answer 3

There are more reactants than products. An example is the combustion of hydrogen to form water.

Question 4

Endothermic Energy Level Diagrams

Answer 4

There are less reactants than products. An example is the decomposition of calcium carbonate.

Question 5

Enthalpy Change

Answer 5

The difference in energy between the reactants and products of a reaction. kJ/mol. Δ H = energy of bonds broken – energy of bonds formed.

Question 6

Exothermic Enthalpy Change

Answer 6

-∆H. In an exothermic reaction, the energy released when new bonds form is greater than the energy needed to break them so the surplus energy is released in the form of heat to the surroundings.

Question 7

Endothermic Enthalpy Change

Answer 7

∆H. the energy needed to break bonds is greater than the energy released when the new bonds form, so energy must be absorbed from the surroundings.

Question 8

Bond energy

Answer 8

the amount of energy in kJ/mol that is needed to break one mole of a bond.

Question 9

Fuels _______

Answer 9

contain stored chemical energy that is released, mainly in the form of heat (and sometimes light), when combusted (burned).

Question 10

Fuel cell

Answer 10

an electrochemical cell that converts chemical energy from fuel into electricity. The hydrogen fuel cell uses hydrogen as its fuel.

Question 11

Oxidation reaction at the hydrogen fuel cell

Answer 11

H 2 → 2H+ + 2e –

Question 12

Reduction reaction at the hydrogen fuel cell

Answer 12

O 2 + 4H + + 4e – → 2H 2 O

Question 13

Total Reaction at the hydrogen fuel cell

Answer 13

2H 2 (g) + O 2 (g) → 2H 2 O(g)

Question 14

Advantages of Hydrogen fuel cells

Answer 14

• Hydrogen produces no carbon emissions, which is better for the environment.
• It has about the same energy content as petrol.
• A source of hydrogen is water, which is in plentiful supply.

Question 15

Disadvantages of Hydrogen fuel cells

Answer 15

• Hydrogen is highly flammable and must be handled carefully.
• It is a gas and therefore has to be compressed for storage. This can be dangerous due to the risk of explosion.
• Most hydrogen comes from the reaction between hydrocarbons, such as methane, and steam. Methane (natural gas) is a fossil fuel and is a non-renewable energy source.

Question 16

How is energy made from radioactive isotopes?

Answer 16

Nuclear fuels are not burned. When the unstable radioactive atoms break down (decay) naturally, they release large amounts of energy. They may also have neutrons fired at them to force their breakdown. The energy given out is used to heat water to generate steam, which then drives a turbine used to generate electricity.

Question 17

Advantages of nuclear power

Answer 17

• There are no carbon dioxide emissions or other pollutant gases, such as sulfur dioxide.
• Nuclear fuel releases large amounts of energy.

Question 18

Disadvantages of nuclear power

Answer 18

• Leakage of nuclear waste can severely affect the life in the area, especially considering mutation.

Question 19

Describe the use of hydrogen as a fuel reacting with oxygen to generate electricity in a fuel cell.

Answer 19

Hydrogen combusts to form water and produce energy to heat up water to steam and turn a turbine.