Energy changes

Question 1

What is an endothermic reaction?

Answer 1

Take in (absorb) energy causing a drop in temperatures in the surroundings (energy enters chemicals)

Question 2

What is an exothermic reaction?

Answer 2

Release energy (emit) causing a temperature increase in the surroundings ( energy exits the chemicals)

Question 3

What are 2 examples of endothermic reactions?

Answer 3

Photosynthesis
Electrolysis

Question 4

What are 3 examples of exothermic reactions?

Answer 4

Combustion
Respiration
Neutralisation

Question 5

What is a calometer?

Answer 5

Measures heat released or absorbed during chemical reactions or physical changes.

Question 6

What is the practical for endo and exothermic reactions?

Answer 6

1. Measure out 10 cm^3 of sodium hydroxide and put in polystyrene cup.
2. Then add 20cm^3 of hydrochloric acid.
3. Record initial and final temps.
4. Rinse cup then repeat with other mixtures.

Question 7

Do exothermic reactions rise or fall in temp?
Does energy rise or fall?

Answer 7

Rise
Fall

Question 8

Do endothermic reactions rise or fall in temp?
Does energy rise or fall?

Answer 8

Fall
Rise

Question 9

What is the mnemic for endo and exo reactions? Are they negative or positive?

Answer 9

Bendo Mexo
Breaking +
Making -

Question 10

What is repeatability?

Answer 10

An experiment keeps having the same results.

Question 11

What is the practical for temperature changes?

Answer 11

1. Put 30cm^3 of dilute hydrochloric acid into a polystyrene cup.
2. Record initial temp.

3.Put 5cm^3 of sodium hydroxide into the cup. When the reading on thermometer stops changing write the temp.

4. Repeat steps adding 5cm^3 more of sodium hydroxide at a time.
5. Find out the mean temp from results.

Question 12

What are fuel cells?
What do they have?
Where are chemicals stored?

Answer 12

An electrical cell which doesn’t need recharging or replacing.
They have a fuel tank that needs refilling.
Chemicals are not stored within the cell.

Question 13

What is the anode and cathode in a fuel cell?

Answer 13

Anode is negative
Cathode is positive

Question 14

What happens in fuel cells when fuel enters?

Answer 14

Fuel becomes oxidised then there is a potential difference across the cell.

Question 15

4 Advantages of hydrogen fuel cells?

Answer 15

Only require hydrogen and oxygen.

Last longer than batteries.

Less polluting to dispose of - doesn’t contribute to global warming and acid rain.

Less landfill during disposal - impact biodiversity.

Question 16

4 Disadvantages of hydrogen fuel cells?

Answer 16

Hydrogen is a gas which takes a lot of space.

Hydrogen is explosive.

Needs energy to generate which comes from fossil fuels.

Energy needed to create H2 gas ( electrolysis of water)

Question 17

What happens at negative and positive electrodes with the examples of magnesium and gold.

Answer 17

Mg -
Au +
Magnesium is more reactive than gold so it transfers more electrons through wire faster forming negative electrode. An electrode forced to accept them forming positive electrode.

Question 18

What is the conclusion of the cell and batteries practical?

Answer 18

The bigger the distance between the metals on reactivity series, bigger the voltage.

Question 19

What is activation energy?

Answer 19

The minimum amount of energy that particles must have to react.

Question 20

Are alkaline batteries rechargable?

Answer 20

No

Question 21

What is the half equation at the anode for fuel cells?

Answer 21

H2 –> 2H^+ + 2e^-

Question 22

What is the half equation at the cathode for fuel cells?

Answer 22

O2 + 4h^+ 4e- —> 2H2O

Question 23

What is the equation for fuel cells?

Answer 23

Chemical energy —-> Electrical energy
2H2 + O2 —> 2H2O