Topic 5 - Energy Changes

Question 1

Are neutralisation reactions exo or endothermic?

Answer 1

exothermic

Question 2

Is thermal decomposition endo or exothermic?

Answer 2

endothermic

Question 3

how can we test the effect of acid concentration on the energy released in a neutralisation reaction?

Answer 3

1.Put 25cm^3 of 0.25mol/dm^3 acid and alkali in separate beakers
2.Place the beakers in a water bath set to 25 degrees until they are both at 25 degrees
3.Add acid followed by the alkali into a polystyrene cup with a lid
4.Take the temperature of the mixture every 30 seconds, and record the highest temp
5.Repeat the previous steps for 0.5mol/dm^3 and 1 mol/dm^3 of acid

Question 4

What is activation energy?

Answer 4

the minimum energy required for a reaction to take place between reacting particles

Question 5

What is an electrochemical cell made up of?

Answer 5

2 electrodes in contact with an electrolyte

Question 6

What is an electrolyte?

Answer 6

an ionic compound that is molten or dissolved in water that conducts electricity and is decomposed by it

Question 7

How do electrochemical cells work?

Answer 7

1. The chemical reactions between the electrodes and the elctrolyte set up a charge difference between the electrodes
2. When the electrodes are connected by a wire, the charge is a ble to flow and electricity is producce

Question 8

What can affect the voltage of an electrochemical cell?

Answer 8

1. The type of electrode
2. The difference in reactivity between the electrodes
3. The electrolyte used in a cell

Question 9

What is a battery?

Answer 9

A series of two or more cells, where the voltages of the cells are combined

Question 10

What is the difference in reactions between a rechargable and non-rechargable cell

Answer 10

The reaction in a rechargable battery is reversible by connecting it to an external electric current, while the reaction in a non-rechargable is irreversible

Question 11

What is a fuel cell?

Answer 11

an electrical cell that uses fuel and oxygen/air to release energy, which is then used to produce electricity.

Question 12

How does a fuel cell work?

Answer 12

When the fuel eneters the cell it becomes oxidised and sets up a potential difference within the cell.

Question 13

What is an example of a fuel cell?

Answer 13

Hydrogen-oxygen fuel cell

Question 14

How does a hydrogen-oxygen fuel cell work?

Answer 14

1. Hydrogen goes into the anode compartment and oxygen goes into the cathode compartment
2. At the anode, hydrogen loses electrons and produces H+ ions - oxidation
3. H+ ions in the electrolyte move to the cathode
4. At the cathode, oxygen gains electrons from the cathode and reacts with H+ ions to make water - reduction
5. The electrons flow through an external circuit from the anode to the cathode - this is the current

Question 15

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

Answer 15

2H2 + O2 —> 2H2O

Hydrogen + Oxygen —> Water

Question 16

What is the half equation at the cathode in a hydrogen-oxygen fuel cell?

Answer 16

O2 + 4H+ + 4e- —-> 2H2O

Question 17

What is the half equation at the anode in a hydrogen-oxygen fuel cell?

Answer 17

H2–> 2H+ + 2e-

Question 18

What is the difference between the anode/cathode in electrolysis vs fuel cells?

Answer 18

in electrolysis the cathode is negative, and the anode is postive - in fuel cells its opposite, cathode is positive and anode is negative

Question 19

What are the pros of hydrogen fuel cells?

Answer 19

1. don’t produce as many pollutants, only releases water as waste product
2. Manufacturing and disposal of a fuel cell is less damaging than electric batteries
3. Fuel cells can be refueled indefinitely
4. Fuel cells usually last longer per refueling than batteries

Question 20

What are the cons of hydrogen fuel cells?

Answer 20

1. Hydrogen gas is very hard to store
2. Hydrogen is explosive when mixed with air
3. hydrogen fuel is often made either from hydrocarbons or by electrolysis, both of which require energy from burning fossil fuels potentially