C1- Energy Changes

Question 1

What does exothermic mean?

Answer 1

Heat is given out

Question 2

What does endothermic mean?

Answer 2

Heat is taken in

Question 3

How is energy moved around in chemical reactions?

Answer 3

Different chemicals store different amounts of energy, if the reaction products store more energy than the original reactants they must have taken in energy from their surroundings. If less, the excess was transferred to the surroundings. The overall amount is the same because energy cannot be created or destroyed.

Question 4

Give 3 examples of an exothermic reaction

Answer 4

Combustion which is the burning of fuels
Neutralisation reactions
Oxidation reactions

Question 5

Give 3 examples of an endothermic reaction

Answer 5

Reaction between Citric Acid and Sodium Hydrogen carbonate
Thermal decomposition
Cooling Packs

Question 6

What do reaction profiles show?

Answer 6

Energy changes

Question 7

Exothermic reaction profile

Answer 7

In book

Question 8

Endothermic reaction profile

Answer 8

In book

Question 9

What happens to bonds in a chemical reaction and is it exo or endo?

Answer 9

Old bonds are broken and new ones are formed. Energy must be supplied for bond breaking making it endo. Energy is released during bond formation making it exo.

Question 10

What is the bond breaking and forming relationship in endothermic and exothermic reactions?

Answer 10

In endothermic reactions the energy used to break bonds is greater than the energy released and vice versa.

Question 11

What is an electrochemical cell?

Answer 11

A basic system made up of two different electrodes in contact with an electrolyte

Question 12

How does an electrochemical cell use chemical reactions to produce electricity?

Answer 12

• The two electrodes must be able to conduct electricity so are usually metals
• The electrolyte is a liquid that contains ions which react with the electrodes
• The chemical reactions between the electrodes and the electrolyte set up a charge difference between the electrodes
• If the electrodes are then connected by a wire, the charge is able to flow and electricity is produced
• A voltmeter can also be connected to the circuit to measure the voltage of the cell

Question 13

What does using different metals (type of electrodes) to react with the same electrolyte cause?

Answer 13

Charge difference or voltage of the cell

Question 14

How does a bigger difference in reactivity of electrodes affect the voltage of the cell?

Answer 14

Causes a bigger voltage of the cell

Question 15

How does the electrolyte used in a cell affect the voltage size?

Answer 15

Different ions in the solution will react differently with different metal electrons

Question 16

How do you form a battery using cells and how does it affect the voltage?

Answer 16

A battery is formed by connecting 2 or more cells together in series, the voltage of the cells is combined causing a larger overall voltage

Question 17

What happens to reactants in non rechargeable batteries?

Answer 17

They are used up

Question 18

Why do reactants get used up in non rechargeable batteries?

Answer 18

In some cells the chemical reactions at the electrodes are irreversible, as overtime the reactants get used up and turned into products, when any one of the reactants is used up the reaction can no longer happen and no electricity is produced

Question 19

How can a reaction be reversed in a rechargeable cell?

Answer 19

By connecting the cell to an external electric current

Question 20

What is a fuel cell and what does it produce?

Answer 20

An electrical cell that is supplied with a fuel and oxygen and uses energy from the reaction between them to produce electrical energy efficiently

Question 21

How does a fuel cell work?

Answer 21

When the fuel enters the cell, it becomes oxidised and sets up a potential difference within the cell

Question 22

What is a good example of a fuel cell?

Answer 22

A hydrogen oxygen fuel cell produces clean water and releases energy

Question 23

What type of reaction does a hydrogen fuel cell involve?

Answer 23

A redox reaction

Question 24

Which electrodes do hydrogen and oxygen go into respectively?

Answer 24

Anode and cathode

Question 25

What could hydrogen fuel cells be used in?

Answer 25

Vehicles

Question 26

Other than hydrogen fuel cells, what is another renewable energy source for cars?

Answer 26

Electrical batteries

Question 27

What are the benefits of using hydrogen fuel cells for vehicles?

Answer 27

• They don’t produce as many pollutants, only by products are water and heat
• Less polluting to dispose of than electric batteries which are made of highly toxic metal compounds
• Batteries are more expensive and can only be recharged so many times before they need to be replaced and they need to be recharged more often

Question 28

What are the disadvantages of using hydrogen fuel cells

Answer 28

• Hydrogen is a gas so it takes a lot more space to store than a battery
• Hydrogen is explosive when mixed with air so it’s hard to store it safely
• The hydrogen is often made from hydrocarbons (from fossil fuels) or electrolysis of water which uses electricity (usually generated by fossil fuels)