AQA GCSE Combined Science: Trilogy · 5.5

Energy changes

50 revision questions with answers for 5.5 Energy changes in AQA GCSE Combined Science: Trilogy (spec 8464). Practise with flashcards, a topic quiz, a random quiz across the course, 5 crosswords, or read every question and answer below. Not official AQA material.

All 50 questions and answers

Question 1 · Spec 5.5.1.1
What is an exothermic reaction?
Answer:
A reaction that transfers energy to the surroundings, increasing their temperature.
Question 2 · Spec 5.5.1.1
What is an endothermic reaction?
Answer:
A reaction that takes in energy from the surroundings, decreasing their temperature.
Question 3 · Spec 5.5.1.1
How is energy conserved during an exothermic reaction?
Answer:
Energy lost by the reacting system is transferred to the surroundings; the total energy remains unchanged.
Question 4 · Spec 5.5.1.1
A reaction mixture warms without external heating. What does this suggest?
Answer:
The reaction is exothermic: energy is transferred to the mixture and surroundings.
Question 5 · Spec 5.5.1.1
A reaction mixture cools below its initial temperature. What does this suggest?
Answer:
The reaction is endothermic: energy is taken in from the mixture and surroundings.
Question 6 · Spec 5.5.1.1
Name three common exothermic reaction types.
Answer:
Combustion, many oxidation reactions and neutralisation.
Question 7 · Spec 5.5.1.1
Give two examples of endothermic reactions.
Answer:
Thermal decomposition and the reaction between citric acid and sodium hydrogencarbonate.
Question 8 · Spec 5.5.1.1
Why are exothermic reactions useful in hand warmers?
Answer:
They transfer energy to the surroundings, warming the user's hands.
Question 9 · Spec 5.5.1.1
Why can an endothermic reaction be useful in a sports injury pack?
Answer:
It absorbs energy from the surroundings, cooling the injured area.
Question 10 · Spec 5.5.1.1
What evidence would help evaluate a self-heating can?
Answer:
Temperature rise, time to reach a useful temperature, heating duration, cost and risks such as excessive temperatures or leakage.
Question 11 · Spec 5.5.1.1 · Required practical
Suggest an independent variable for the temperature-change practical.
Answer:
The concentration of one reacting solution, while controlling the other reactant and measurement conditions.
Question 12 · Spec 5.5.1.1 · Required practical
What is the dependent variable when comparing reaction heating effects?
Answer:
The temperature change of the reaction mixture.
Question 13 · Spec 5.5.1.1 · Required practical
Which variables should be controlled when testing concentration's effect?
Answer:
Solution volumes, initial temperature, other reactant amount, container and mixing method.
Question 14 · Spec 5.5.1.1 · Required practical
Why use an insulated cup rather than an uninsulated metal container?
Answer:
It reduces energy transfer to the surroundings, giving a temperature change closer to that caused by the reaction.
Question 15 · Spec 5.5.1.1 · Required practical
Why can a lid improve a temperature-change investigation?
Answer:
It reduces energy transfer to the surroundings, including loss through evaporation.
Question 16 · Spec 5.5.1.1 · Required practical
Why should the mixture be stirred gently before reading temperature?
Answer:
Stirring makes temperature more uniform, so the thermometer samples the mixture more representatively.
Question 17 · Spec 5.5.1.1 · Required practical
Why record the highest or lowest temperature reached?
Answer:
The mixture later exchanges energy with the surroundings, reducing the observed change from the reaction.
Question 18 · Spec 5.5.1.1 · Required practical
What does thermometer resolution mean?
Answer:
The smallest temperature change that the thermometer can display or its scale can distinguish.
Question 19 · Spec 5.5.1.1 · Required practical
Outline a method for measuring neutralisation's temperature change.
Answer:
Measure equal starting temperatures, mix measured acid and alkali volumes in an insulated cup, stir and record the maximum temperature.
Question 20 · Spec 5.5.1.1 · Required practical
A mixture warms from 19.5 °C to 27.0 °C. Calculate temperature change.
Answer:
Temperature change = 27.0 − 19.5 = +7.5 °C; the warming suggests an exothermic reaction.
Question 21 · Spec 5.5.1.1 · Required practical
A mixture cools from 22.0 °C to 16.5 °C. Calculate temperature change.
Answer:
Temperature change = 16.5 − 22.0 = -5.5 °C; the cooling suggests an endothermic reaction.
Question 22 · Spec 5.5.1.1 · Required practical
Temperature rises are 6.1, 6.3 and 6.2 °C. Find the mean.
Answer:
Mean rise = (6.1 + 6.3 + 6.2) / 3 = 6.2 °C.
Question 23 · Spec 5.5.1.1 · Required practical
Temperature rises range from 5.8 to 6.4 °C. Find their range.
Answer:
Range = 6.4 − 5.8 = 0.6 °C.
Question 24 · Spec 5.5.1.1 · Required practical
One temperature rise is much lower than the repeats. What should be checked?
Answer:
Check quantities, initial temperatures, mixing, timing and possible energy losses; repeat before deciding whether exclusion is justified.
Question 25 · Spec 5.5.1.1 · Required practical
Why should reactants start at the same temperature in a comparison?
Answer:
Otherwise initial temperature differences could affect the measured change independently of the reaction variable.
Question 26 · Spec 5.5.1.1 · Required practical
Why is comparing temperature rises unfair if solution volumes differ greatly?
Answer:
Different amounts of solution need different amounts of energy for the same temperature rise, so volume becomes a confounding variable.
Question 27 · Spec 5.5.1.1 · Required practical
Suggest a concentration hypothesis for neutralisation with the other reactant in excess.
Answer:
At fixed volumes, a higher acid concentration may produce a larger temperature rise because more acid reacts.
Question 28 · Spec 5.5.1.1 · Required practical
Why can a temperature-time graph improve the record of a reaction?
Answer:
It shows the initial temperature, rise or fall and later return towards room temperature, helping identify the extreme value.
Question 29 · Spec 5.5.1.1 · Required practical
Why might a no-reaction control be useful in a temperature investigation?
Answer:
It shows temperature drift caused by mixing or surroundings rather than the intended chemical reaction.
Question 30 · Spec 5.5.1.1 · Required practical
Why does energy loss usually make an exothermic temperature rise too small?
Answer:
Some released energy leaves the mixture before measurement, so less remains to raise its temperature.
Question 31 · Spec 5.5.1.2
What are the axes on a reaction profile?
Answer:
Vertical: energy. Horizontal: progress of the reaction, not time.
Question 32 · Spec 5.5.1.2
Where are reactants and products shown on a reaction profile?
Answer:
Reactants are at the starting energy level; products are at the finishing energy level.
Question 33 · Spec 5.5.1.2
How does an exothermic reaction profile show energy transfer?
Answer:
The products lie at a lower energy level than the reactants.
Question 34 · Spec 5.5.1.2
How does an endothermic reaction profile show energy transfer?
Answer:
The products lie at a higher energy level than the reactants.
Question 35 · Spec 5.5.1.2
Define activation energy.
Answer:
The minimum energy that colliding particles must have for a reaction to occur.
Question 36 · Spec 5.5.1.2
Where is activation energy shown on a reaction profile?
Answer:
The vertical energy difference from the reactant level to the top of the curve.
Question 37 · Spec 5.5.1.2
Why may a fuel need a spark even though combustion is exothermic?
Answer:
The spark supplies energy to overcome the activation-energy barrier and start the reaction.
Question 38 · Spec 5.5.1.2
Which profile feature identifies overall energy change?
Answer:
The vertical difference between reactant and product energy levels, rather than the height of the peak alone.
Question 39 · Spec 5.5.1.2
Does a higher activation-energy peak mean a reaction is more exothermic?
Answer:
No. Exothermicity depends on the difference between reactant and product levels, not the peak's height.
Question 40 · Spec 5.5.1.2
Can you read reaction duration directly from a reaction profile?
Answer:
No. Its horizontal axis is reaction progress, so it does not provide a time scale.
Question 41 · Spec 5.5.1.3 · Higher only
Is bond breaking exothermic or endothermic?
Answer:
Endothermic: energy must be supplied to break a bond.
Question 42 · Spec 5.5.1.3 · Higher only
Is bond formation exothermic or endothermic?
Answer:
Exothermic: energy is released when bonds form.
Question 43 · Spec 5.5.1.3 · Higher only
State the bond-energy calculation for overall energy change.
Answer:
Energy change = total energy needed to break reactant bonds - total energy released forming product bonds.
Question 44 · Spec 5.5.1.3 · Higher only
Explain an exothermic reaction in terms of bond energies.
Answer:
Forming product bonds releases more energy than is needed to break reactant bonds.
Question 45 · Spec 5.5.1.3 · Higher only
Explain an endothermic reaction in terms of bond energies.
Answer:
Breaking reactant bonds requires more energy than forming product bonds releases.
Question 46 · Spec 5.5.1.3 · Higher only
Breaking bonds requires 900 kJ/mol and forming bonds releases 1,200 kJ/mol. Find the change.
Answer:
900 − 1,200 = -300 kJ/mol; the reaction is exothermic.
Question 47 · Spec 5.5.1.3 · Higher only
Breaking bonds requires 1,100 kJ/mol and forming bonds releases 850 kJ/mol. Find the change.
Answer:
1,100 − 850 = +250 kJ/mol; the reaction is endothermic.
Question 48 · Spec 5.5.1.3 · Higher only
H₂ + Cl₂ → 2HCl. Bond energies: H-H 436, Cl-Cl 243, H-Cl 431 kJ/mol. Calculate the change.
Answer:
Broken: 436 + 243 = 679. Formed: 2 × 431 = 862. Change = -183 kJ/mol.
Question 49 · Spec 5.5.1.3 · Higher only
2H₂ + O₂ → 2H₂O. Bond energies: H-H 436, O=O 498, O-H 464 kJ/mol. Calculate the change for the equation.
Answer:
Broken: 2 × 436 + 498 = 1,370. Formed: 4 × 464 = 1,856. Change = -486 kJ per equation as written.
Question 50 · Spec 5.5.1.3 · Higher only
Why must coefficients be considered in bond-energy calculations?
Answer:
They determine the number of molecules and therefore the total number of each bond broken or formed.

← 5.4 Chemical changes 5.6 The rate and extent of chemical change →

More AQA GCSE Combined Science: Trilogy topics

Other Combined science courses: Pearson Edexcel GCSE Combined Science.

Energy changes

All 50 questions and answers

More AQA GCSE Combined Science: Trilogy topics

Cookies on Knowledge Noodles

Cookie settings