1.
State what is meant by an exothermic reaction.
[1 mark]
- a reaction that transfers energy to the surroundings
JD SCIENCE
Energy changes
Indicative marking points. Award marks for equivalent scientific or mathematical wording. Do not issue this sheet with the student worksheet.
2.
State what is meant by an endothermic reaction.
[1 mark]
- a reaction that takes in energy from the surroundings
3.
State what is meant by activation energy.
[1 mark]
- the minimum energy particles need to react
4.
State what is meant by a reaction profile.
[1 mark]
- a diagram of energy against progress of reaction
5.
State what is meant by bond energy.
[1 mark]
- energy needed to break one mole of a bond
6.
State what is meant by a catalyst.
[1 mark]
- speeds up a reaction without being used up
7.
State what is meant by cells and batteries.
[1 mark]
- chemical reactions that produce a potential difference
8.
State what is meant by a fuel cell.
[1 mark]
- a cell that produces electricity from a fuel and oxygen
9.
State what is meant by conservation of energy in reactions.
[1 mark]
- energy is transferred, not created
10.
State what is meant by a chemical cell.
[1 mark]
- two metals in an electrolyte produce a voltage
11.
Amira is asked about an exothermic reaction in a AQA Chemistry paper.
(a) [2 marks]
- temperature of surroundings increases
(b) [3 marks]
- why hand warmers are exothermic
12.
Amira is asked about an endothermic reaction in a AQA Chemistry paper.
(a) [2 marks]
- temperature falls
(b) [3 marks]
- why sports injury packs can be endothermic
13.
Amira is asked about activation energy in a AQA Chemistry paper.
(a) [2 marks]
- shown on a reaction profile
(b) [3 marks]
- why a catalyst increases rate
14.
Amira is asked about a reaction profile in a AQA Chemistry paper.
(a) [2 marks]
- shows Ea and energy change
(b) [3 marks]
- how to tell exothermic from the profile
15.
Amira is asked about bond energy in a AQA Chemistry paper.
(a) [2 marks]
- breaking is endothermic, making is exothermic
(b) [3 marks]
- why a reaction is exothermic overall
16.
Amira is asked about a catalyst in a AQA Chemistry paper.
(a) [2 marks]
- not in the overall equation
(b) [3 marks]
- why catalysts are useful in industry
17.
Bonds broken 2000 kJ, bonds made 2500 kJ. Energy change?
[3 marks]
- made − broken
- Final answer: −500 kJ (exothermic)
18.
Q = mcΔT. 50 g water, c=4.2, ΔT=12°C. Calculate Q.
[3 marks]
- Final answer: 2520 J
19.
That Q came from 0.010 mol of fuel. Energy per mole?
[3 marks]
- Final answer: 252 kJ/mol
20.
A reaction profile has reactants at 80 kJ and products at 30 kJ. ΔH?
[3 marks]
- Final answer: −50 kJ
21.
Ea is 60 kJ/mol without a catalyst and 25 kJ/mol with. By how much has Ea fallen?
[3 marks]
- Final answer: 35 kJ/mol
22.
A fuel cell uses 2H₂ + O₂ → 2H₂O. Moles of H₂O from 4 mol H₂?
[3 marks]
- ratio 2:2
- Final answer: 4 mol
23.
Amira carries out temperature change of neutralisation or displacement. This is a typical AQA required-practical style question.
(a) [2 marks]
- Independent: combination of reagents
- Dependent: temperature change
(b) [2 marks]
- same volumes, insulated cup
- so the test is fair / only one variable is changed
(c) [2 marks]
- heat loss to the air
24.
Amira carries out comparing fuels by heating water. This is a typical AQA required-practical style question.
(a) [2 marks]
- Independent: fuel
- Dependent: ΔT of water
(b) [2 marks]
- same mass of water, same distance of flame
- so the test is fair / only one variable is changed
(c) [2 marks]
- incomplete combustion / draughts
25.
Amira carries out drawing reaction profiles from experimental ΔT data. This is a typical AQA required-practical style question.
(a) [2 marks]
- Independent: reaction
- Dependent: calculated energy change
(b) [2 marks]
- same calorimeter
- so the test is fair / only one variable is changed
(c) [2 marks]
- not stirring so ΔT is wrong
26.
Amira carries out investigating chemical cells with different metal pairs. This is a typical AQA required-practical style question.
(a) [2 marks]
- Independent: metal pair
- Dependent: voltage
(b) [2 marks]
- same electrolyte
- so the test is fair / only one variable is changed
(c) [2 marks]
- poor contact / corroded metals
27.
Compare exothermic with endothermic.
[4 marks]
- exothermic: energy out, products lower
- endothermic: energy in, products higher
28.
Compare a battery with a hydrogen fuel cell.
[4 marks]
- battery: stored chemicals, goes flat
- fuel cell: continuous fuel supply, water product
29.
Compare bond breaking with bond making.
[4 marks]
- breaking takes in energy
- making releases energy
30.
Compare a catalyst with an increased temperature.
[4 marks]
- catalyst: lower Ea, not used up
- temperature: more particles have Ea, rate up
31.
Apply your knowledge of cells and batteries to this situation: the reaction is reversed when charging
[3 marks]
- the reaction is reversed when charging
32.
Apply your knowledge of a fuel cell to this situation: only water emitted vs hydrogen storage issues
[3 marks]
- only water emitted vs hydrogen storage issues