Which equation below can represent both an enthalpy change of formation and combustion?
CH4 (g) + 2O2 (g) → CO2 (g) + 2H2O (l)
2Na (s) + ½O2 (g) → Na2O (s)
HCl (aq) + NaOH (aq) → NaCl (aq) + H2O (l)
C (s) + O2 (g) → CO2 (g)
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Syllabus Edition
First teaching 2023
First exams 2025
Which equation below can represent both an enthalpy change of formation and combustion?
CH4 (g) + 2O2 (g) → CO2 (g) + 2H2O (l)
2Na (s) + ½O2 (g) → Na2O (s)
HCl (aq) + NaOH (aq) → NaCl (aq) + H2O (l)
C (s) + O2 (g) → CO2 (g)
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A student carried out an experiment to determine the enthalpy change for the combustion of ethanol.
The following results were obtained by the student. The specific heat capacity of water is 4.18 J g−1 K−1.
start temperature of the water |
21 °C |
final temperature of the water |
41 °C |
mass of alcohol burner before burning |
259.75 g |
mass of alcohol burner after burning |
259.18 g |
mass of glass beaker plus water |
150.00 g |
mass of glass beaker |
50.0 g |
How much of the heat energy produced by the burning of ethanol went into the water?
8 360 J
12 540 J
47.65 J
17 138 J
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When a sample of ammonium chloride is added to a small beaker of water and stirred, the temperature drops as the ammonium chloride slowly dissolves in the water.
Which statement about the process is true?
The process is endothermic and ΔH is -
The process is exothermic and ΔH is -
The process is endothermic and ΔH is +
The process is exothermic and ΔH is +
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Which statement is true about all exothermic reactions?
Gases are formed during the reaction
They give out heat
The reaction is fast
They are combustion reactions
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Which processes have a negative enthalpy change?
I and II only
I and III only
II and III only
I, II and III
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The enthalpy change of a chemical reaction can be found using the following relationship:
q = mcΔT
In this expression, which of the following is true?
m represents the amount of substance in moles
The temperature is measured in Centigrade
c is the specific heat capacity of the substance
The unit of q is kJ
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Which is the correct definition for the standard enthalpy of combustion?
The enthalpy change when the reactants in a stoichiometric equation react to give the products, under standard conditions
The enthalpy change when one mole of a substance is burnt in excess oxygen, under standard conditions
The enthalpy change when one mole of water is formed by reacting an acid and an alkali, under standard conditions
The enthalpy change when one mole of a product is formed from its elements, under standard conditions
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1.20 g of ethanol is combusted releasing 35 500 J of energy.
What is the molar enthalpy change for the combustion of ethanol?
–1 363 kJ mol-1
–11 646 kJ mol-1
1 363 kJ mol-1
642 836 kJ mol-1
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Which enthalpy change is described as the enthalpy change when the reactants in a stoichiometric equation react, under standard conditions, to form the products?
ΔHӨc
ΔHӨneut
ΔHӨr
ΔHӨf
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Enthalpy of formation data is often used to calculate the enthalpy of reaction. Which of the following does not have a standard enthalpy of formation of 0 kJ mol-1?
C (s)
N2 (l)
O2 (g)
F2 (g)
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The reaction pathway for a reversible reaction is shown below:
Which statement is correct?
The activation energy of the reverse reaction is +90 kJ mol–1
The activation energy of the forward reaction is +20 kJ mol–1
The activation of the reverse reaction is +20 kJ mol–1
The enthalpy change of forwards reaction is - 70 kJ mol–1
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The reaction pathway for a reversible reaction is shown below.
Which statements are correct?
I and II only
I and III only
II and III only
I, II and III
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When a sample of calcium oxide, CaO, is added to dilute hydrochloric acid the temperature rises. Which of the following statements is correct?
More bonds are broken than are formed in the reaction
More bonds are formed than are broken in the reaction
The energy of the bonds broken is greater than of the bonds formed
The energy of the bonds broken is less than of the bonds formed
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This energy profile diagram represents the reaction pathway for the following reaction:
Y (g) + Z (g) → W (g) + X (g)
Which statement is true about the reverse reaction, W(g) + X(g) → Y(g) + Z(g)?
It will have a negative ΔH
It will have a positive ΔH
It will have a smaller activation energy
The temperature of the surroundings increase
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The reaction of hydrogen with iodine to form hydrogen iodide is shown below:
H2 + I2 → 2HI
Use the bond energy data given to calculate the enthalpy of reaction, ΔHӨr.
Bond |
Energy, kJ mol-1 |
H-H |
432 |
I-I |
151 |
H-I |
298 |
881 kJ mol–1
1 179 kJ mol–1
–13 kJ mol–1
285 kJ mol–1
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A student mixed 30.0 cm3 of 0.0250 mol dm-3 potassium hydroxide solution with 30.0 cm3 of 0.0250 mol dm-3 nitric acid. The temperature rose by 0.50 oC. Assume no heat was lost to the surroundings.
The mixture had a specific heat capacity of 4.18 J g -1 K-1.
What is the molar enthalpy change for the reaction?
–83 600
–167 200 kJ mol–1
– 5.98 x 10–6 kJ mol–1
–167.2 kJ mol–1
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An experiment was carried out to determine the approximate value for the molar enthalpy change of neutralisation.
75 cm3 of 3.00 mol dm–3 hydrochloric acid was placed in a polystyrene beaker of negligible heat capacity. Its temperature was recorded, and then 75 cm3 of 3.00 mol dm−3 potassium hydroxide at the same temperature was quickly added, and the solution stirred.
The temperature rose by 14 °C. The resulting solution may be considered to have a specific heat capacity of 4.18 J g-1 K-1.
What is the value for ΔH?
–4 876.7 J mol–1
–39 013 J mol–1
–39.01 J mol–1
–99 972 J mol–1
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The table below discusses three types of enthalpy change:
‘+’ means that this type of standard enthalpy change can only have positive values,
‘–’ means that this type of standard enthalpy change can only have negative values,
‘+ / –’ means that either positive or negative values are possible.
Which row is correct?
formation |
combustion |
neutralisation |
|
A |
+ |
+ |
+ / – |
B |
+ / – |
+ |
+ / – |
C |
+ / – |
– |
– |
D |
– |
– |
+ |
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Using a spirit burner, ethanol is used to heat a container of water.
In this experiment:
Mass of ethanol burned, g |
a |
Mass of water, g |
b |
Specific heat capacity of water, J g–1 K–1 |
d |
Temperature rise, °C |
y |
How much heat energy is absorbed by the water?
ady
bdy
bd(y+273)
(y+273) / ad
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An iron block with a mass of 0.11 kg absorbs 504 J of heat energy. What is the temperature rise in K?
Specific heat capacity of iron = 0.448 J g–1 K–1
1.02 x104
1.10
10.23
9.78 x 10-2
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Which statements are correct for an endothermic reaction?
I and II only
I and III only
II and III only
I, II and III
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Which assumptions are correct when calculating the enthalpy change for a reaction in solution?
I and II only
I and III only
II and III only
I, II and III
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What is the closest integer value of the temperature change for this reaction, from the graph
8
9
11
35
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Which enthalpy changes correctly describe the following reactions?
Reaction 1: HNO3 (aq) + NH3 (aq) → NH4NO3 (aq)
Reaction 2: CuCO3 (s) → CuO (s) + CO2 (g)
Reaction 3: S (s) + O2 (g) → SO2 (g)
ΔHӨc |
ΔHӨf |
ΔHӨneut |
ΔHӨr |
|
A |
2 |
2 |
1 |
3 |
B |
3 |
2 |
1 |
2 |
C |
3 |
3 |
1 |
2 |
D |
2 |
3 |
1 |
3 |
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Hess’s Law can be used to calculate the enthalpy change for reactions that are difficult to measure experimentally, such as the conversion of graphite to diamond.
Which enthalpy data could be used to calculate the enthalpy change for the conversion of graphite to diamond?
I and II only
I and III only
II and III only
I, II and III
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Compound R into compound T, it was found that the reaction proceeded by way of compound S, which could be isolated. The following steps were involved.
R → S; ΔH is positive
S → T; ΔH is negative
Which reaction profile fits these data?
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The reaction pathway for an endothermic reaction is shown.
Which arrow represents the activation energy for the reverse reaction?
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The reaction pathway shows the energies of the reactants, the products and the transition state of a reaction.
Which expression correctly represents how to calculate the activation energy of the forward reaction?
E3 – E2
E2 – E1
E2 – E3
E1 – E2
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Four possible reactions (A, B, C and D) of the following equation are measured at the same temperature.
X (g) + Y (g) → Z (g)
Which reaction pathway diagram shows the reaction occurring rapidly with an overall negative enthalpy value?
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Which combination about bond breaking and bond formation energy changes is correct?
|
Bond breaking |
Bond formation |
A |
endothermic |
endothermic |
B |
endothermic |
exothermic |
C |
exothermic |
endothermic |
D |
exothermic |
exothermic |
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In a calorimetric experiment 2.50 g of a fuel is burnt in oxygen. 30 % of the energy released during the combustion is absorbed by 500 g of water, the temperature of which rises from 25 °C to 68 °C.
The specific heat capacity of water is 4.18 J g–1 K–1.
What is the total energy released per gram of fuel burnt?
35 948 J
880 587 J
119 827 J
299 567 J
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The reaction of hydrochloric acid with sodium hydroxide produced an overall temperature of 24.4 oC.
Given the following data, how much thermal energy was evolved during this reaction?
Initial temperature of 25.0 cm3 hydrochloric acid = 17.6 oC
Initial temperature of 25.0 cm3 sodium hydroxide = 18.5 oC
The specific heat capacity of water is 4.18 J g-1 K-1.
1327 J
380 J
209 J
2654 J
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The temperature rise when 0.1 MJ of heat energy is absorbed by 2.5 kg of solid aluminium is 44.4 oC.
What is the specific heat capacity of aluminium, in J g-1 K-1?
901 J g-1 K-1
0.900 J g-1 K-1
9.00 x 10–4 J g-1 K-1
9.00 x 10-6 J g-1 K-1
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An iron cube, with a mass of 0.5 kg, increases in temperature by 12.7 K when heated.
The specific heat capacity of iron is 0.448 J K-1 g-1.
What is the enthalpy change, in kJ mol–1, for heating the iron cube?
318 kJ mol–1
25.5 kJ mol–1
0.318 kJ mol–1
-0.318 kJ mol–1
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When completing experiments to measure enthalpy change for exothermic processes, which of the following is not a reason for the experimental data to be lower than the expected value?
Heat loss through convection
Water vapour released as a product
An inadequate supply of oxygen during combustion
Heat transfer to the system
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Heptathiepane, S7, can undergo complete combustion to form sulfur dioxide.
S7 (s) + 7O2 (g) → 7SO2 (g)
Which enthalpy changes can be used to describe this reaction?
|
ΔHfθ |
ΔHcθ |
ΔHr |
A |
✓ |
x |
✓ |
B |
x |
✓ |
✓ |
C |
x |
✓ |
x |
D |
x |
x |
✓ |
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A student obtained the following experimental results for the enthalpy of combustion of cyclohexane (C6H12).
Mass of water / g |
50.00 |
Initial temperature of the water / °C |
19.60 |
Initial mass of spirit burner and cyclohexane / g |
186.79 |
Final mass of spirit burner and cyclohexane / g |
186.29 |
The student determined from this experiment that the enthalpy of combustion of cyclohexane is –1216 kJ mol–1
The specific heat capacity of water = 4.18 J g–1 K–1
The relative molecular mass (Mr) of cyclohexane = 84.18
What is the final temperature of the water in this experiment?
19.63 °C
54.16 °C
999.14 °C
979568.69 °C
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The diagrams below show a simple calorimeter that is commonly used in the school laboratory and the more accurate chamber calorimeter.
Simple calorimeter |
Chamber calorimeter |
Which of the following statements correctly explain why the chamber calorimeter is more accurate?
I and II only
I and III only
II and III only
I, II and III
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Which of the following assumptions are correct when completing the calorimetry experiment and subsequent calculations for the neutralisation of 25.0 cm3 sulfuric acid by 25.0 cm3 barium hydroxide?
I and II only
I and III only
II and III only
I, II and III
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The heat produced by the combustion of magnesium is used to heat some water.
Which values are needed to calculate the energy transferred during the reaction?
I and II only
I and III only
II and III only
I, II and III
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