Topic 5

Question 1

What is energy moved around by?

Answer 1

chemical reactions

Question 2

What do chemicals store?

Answer 2

a certain amount of energy and different chemicals store different amounts

Question 3

What happens if the products of a reaction store less energy than the original reactants?

Answer 3

the excess energy was transferred to the surroundings during the reaction

Question 3

What happens if the products of a reaction store more energy than the original reactants?

Answer 3

they must have taken in the difference in energy between the products and reactants from the surroundings during the reaction.

Question 4

Why does the overall amount of energy in a reaction not change?

Answer 4

because energy is conserved in reactions - it can’t be created or destroyed, only moved around. This means the amount of energy in the universe always stays the same.

Question 5

What happens to heat in an exothermic reaction?

Answer 5

heat is given out

Question 6

What is an exothermic reaction?

Answer 6

one which transfers energy to the surroundings, usually by heating. This is shown by a rise in temperature

Question 7

Give examples of an exothermic reactions.

Answer 7

-combustion (burning fuels) this gives out a lot of energy so it’s very exothermic.
-neutralisation reactions
-many oxidation reactions

Question 8

What are some everyday uses of exothermic reaction?

Answer 8

-some hand warmers use the exothermic oxidation of iron in air with a salt solution catalyst to release energy
-self heating cans of hot chocolate and coffee also rely on exothermic reactions between chemicals in their bases

Question 9

What happens to heat in an endothermic reaction?

Answer 9

heat is taken in

Question 10

What is an endothermic reaction?

Answer 10

is a reaction which takes in energy from the surroundings. This is shown by a fall in temperature.

Question 11

Are exothermic or endothermic reactions more common?

Answer 11

exothermic reactions are more common

Question 12

What are some examples of endothermic reaction?

Answer 12

-the reaction between citric acid and sodium hydrogen carbonate
-thermal decomposition

Question 13

What are some everyday uses of endothermic reactions?

Answer 13

sports injury packs - the chemical reaction allows the pack to become instantly cooler without having to put it in a freezer.

Question 14

What is needed to break bonds and is breaking bonds endothermic or exothermic?

Answer 14

Energy must be supplied to break existing bonds - so it’s an endothermic process

Question 15

What happens when bonds are made and is making bonds endothermic or exothermic?

Answer 15

Energy is released when new bonds form - so is an exothermic process

Question 16

What is the formula for the overall energy change?

Answer 16

overall energy change = energy required to break bonds -energy released by forming bonds

Question 17

What is an electrochemical cell?

Answer 17

a basic system made up of different electrodes in contact with electrolyte.

Question 18

What are electrode usually?

Answer 18

metals as they must be able to conduct electricity

Question 19

What is an electrolyte?

Answer 19

An electrolyte is a liquid that contains ions which react with the electrodes

Question 20

How can a simple cell be made?

Answer 20

A simple cell be made by connecting two different metals in contact with an electrolyte.

Question 21

What does the voltage produced by a cell depend on?

Answer 21

The voltage produced by a cell is depends on the type of electrode and electrolyte

Question 22

What happens in non-rechargeable cells and batteries when one of the reactants has been used up? Give an example of a non-rechargeable battery.

Answer 22

The chemical reactions stop when one of the reactants has been used up. Alkaline batteries are non-rechargeable.

Question 23

Why can rechargeable cells and batteries can be recharged?

Answer 23

Because the chemical reactions are reversed when an external electrical current is supplied.

Question 24

What do fuel cells use to produce electrical energy?

Answer 24

fuel and oxygen

Question 25

What is a fuel cell?

Answer 25

A fuel cell is an electrical cell that's supplied with fuel and oxygen and uses energy from the reaction between them to produce electrical energy efficiently.

Question 26

What happens when fuel enters the fuel cell?

Answer 26

it becomes oxidised and sets up a potential difference within the cell

Question 27

Give an example of a different type of fuel cell.

Answer 27

Hydrogen-Oxygen fuel cells. This fuel cell combines hydrogen and oxygen to produce nice clean water and release energy

Question 28

What type of reaction does a hydrogen-oxygen fuel cell involve?

Answer 28

a redox reaction

Question 29

What are the electrolyte and electrodes often in a hydrogen-oxygen fuel cell?

Answer 29

The electrolyte is often an acid such as phosphoric acid. The electrodes are often porous carbon with a catalyst.

Question 30

In a hydrogen-oxygen fuel cell what goes into the anode compartment and what goes into the cathode compartment?

Answer 30

Hydrogen goes into the anode compartment and oxygen goes into the cathode compartment.

Question 31

What is oxidation in terms of a hydrogen-oxygen fuel cell? What is the half equation that shows this?

Answer 31

At the -ve electrode (the anode), hydrogen loses electrons to produce H+ ions. H ---> 2H+ + 2e- 2

Question 32

What is reduction in terms of a hydrogen-oxygen fuel cell? What is the half equation that shows this?

Answer 32

At the +ve electrode (the cathode), oxygen gains electrons from the cathode and reacts with H+ ions from the acidic electrolyte to make water. O + 4H+ + 4e- ----> 2H O 2 2

Question 33

What is the overall reaction in a hydrogen-oxygen fuel cell?

Answer 33

Hydrogen plus oxygen gives water 2H + O ---> 2H O 2 2 2

Question 34

How are fuel cells better than batteries in vehicles?

Answer 34

-Fuel cell vehicles don't produce as many pollutants as other fuels. Electric vehicles don't produce many pollutants either but their batteries are more polluting to dispose than fuel cells because they're made from highly toxic metal compounds. -Batteries in electric vehicles are rechargeable but there's a limit to how many times they can be recharged before they need replacing -Batteries are more expensive to make than fuel cells -Batteries also store less energy than fuel cells and so would need to be recharged more often which can take a long time

Question 35

What are some disadvantages of using hydrogen fuel cells?

Answer 35

-Hydrogen is a gas, so it takes up loads more space to store than a rechargeable battery. -Hydrogen is explosive when mixed with air so it's hard to store safely