AQA AS-LEVEL CHEMISTRY PAPER 2 EXAM (7404/2)-ORGANIC
AND PHYSICAL CHEMISTRY| PRACTICE QUESTIONS AND
ANSWERS 2026/2027 | COMPLETE QUESTIONS AND ANSWERS
(VERIFIED ANSWERS) | EXAM PREP | COMPREHENSIVE EXAM
GUIDE 2026&2027
1. Which statement correctly describes the enthalpy change of combustion of a substance?
A. The enthalpy change when one mole of a substance is completely decomposed
B. The enthalpy change when one mole of a substance is completely burned in oxygen under
standard conditions
C. The energy required to break all bonds in one mole of a substance
D. The enthalpy change when one mole of a substance dissolves in water
Answer: B
The enthalpy change of combustion is the enthalpy change when one mole of a substance
undergoes complete combustion in oxygen under specified conditions.
2. A student measures the temperature rise when a known mass of ethanol is burned
beneath a copper calorimeter containing water. Which change would most directly reduce
heat loss to the surroundings?
A. Using a larger volume of water
B. Increasing the distance between the flame and calorimeter
C. Using a draught shield around the apparatus
D. Using a larger spirit burner
Answer: C
A draught shield reduces heat transfer from the flame and heated apparatus to the
surrounding air, improving the proportion of released energy transferred to the water.
3. Which equation represents the standard enthalpy change of formation of carbon
dioxide?
A. C(s) + O₂(g) → CO₂(g)
B. 2C(s) + O₂(g) → 2CO₂(g)
C. CO(g) + ½O₂(g) → CO₂(g)
D. C(s) + ½O₂(g) → CO(g)
Answer: A
,The standard enthalpy of formation is the enthalpy change when one mole of a compound is
formed from its elements in their standard states.
4. Why are bond enthalpy calculations described as approximate?
A. Bond enthalpies are measured only at very low temperatures
B. Bond enthalpies depend on the number of electrons in the atom
C. Bond enthalpies are calculated from ionic compounds only
D. Bond enthalpy values are mean values obtained from different compounds
Answer: D
Bond enthalpies are average values for a particular bond in different molecules, so they do
not represent the exact bond energy in every individual compound.
5. A reaction has a negative enthalpy change. Which statement is correct?
A. Energy is transferred from the surroundings to the reacting system
B. The products have greater enthalpy than the reactants
C. Energy is transferred from the reacting system to the surroundings
D. The reaction must have a negative activation energy
Answer: C
A negative enthalpy change indicates an exothermic reaction in which energy is released from
the reacting system to the surroundings.
6. Which expression can be used to calculate the heat energy transferred to water during a
calorimetry experiment?
A. q = mcΔT
B. q = mΔT/c
C. q = cΔT/m
D. q = mc/T
Answer: A
The heat transferred is calculated using q = mcΔT, where m is mass, c is specific heat capacity
and ΔT is temperature change.
,7. A student obtains a temperature increase of 8.4 °C when burning a fuel. The expected
temperature increase is 11.2 °C. What is the most likely explanation?
A. The fuel has no enthalpy change
B. Some heat was lost to the surroundings
C. The water absorbed no energy
D. The combustion was necessarily endothermic
Answer: B
Heat loss to the surroundings causes the measured temperature rise to be smaller than the
theoretical value, leading to an underestimated magnitude of enthalpy change.
8. Which change would make a bond enthalpy calculation more accurate?
A. Using ionic equations instead of molecular equations
B. Ignoring bonds in gaseous molecules
C. Using average bond enthalpy data appropriate to the bonds involved
D. Using only the strongest bond in each molecule
Answer: C
The calculation depends on correctly identifying every bond broken and formed and using
appropriate mean bond enthalpy values.
9. In an exothermic reaction, which statement about the energy profile is correct?
A. Products are at a lower energy level than reactants
B. Products are at a higher energy level than reactants
C. Reactants and products have identical energies
D. Activation energy is always zero
Answer: A
For an exothermic reaction, the products have lower enthalpy than the reactants because
energy has been released to the surroundings.
10. A student calculates an enthalpy change using a temperature increase that was
recorded to only one decimal place. Which quantity limits the precision of the final
answer?
A. The colour of the solution
B. The precision of the measured temperature change
, C. The atmospheric pressure only
D. The shape of the thermometer
Answer: B
The precision of experimental measurements affects the precision of the calculated enthalpy
change.
11. Which statement correctly describes dynamic equilibrium?
A. Reactants and products have equal concentrations
B. The forward reaction has stopped
C. The reverse reaction has stopped
D. Forward and reverse reactions occur at equal rates
Answer: D
At dynamic equilibrium, both reactions continue, but their rates are equal, so macroscopic
concentrations remain constant.
12. A reversible reaction reaches equilibrium in a sealed container. What happens if the
concentration of a reactant is increased?
A. The equilibrium constant increases
B. The equilibrium constant decreases
C. The equilibrium position may shift to oppose the change
D. Both reactions immediately stop
Answer: C
According to Le Chatelier's principle, increasing the concentration of a reactant causes the
equilibrium position to shift in the direction that reduces the added reactant.
13. Which statement about the equilibrium constant Kc is correct?
A. Its value changes when equilibrium concentrations change at constant temperature
B. Its value is fixed for a particular reaction at a specified temperature
C. It always has a value of 1 at equilibrium
D. It is unaffected by temperature
Answer: B
AND PHYSICAL CHEMISTRY| PRACTICE QUESTIONS AND
ANSWERS 2026/2027 | COMPLETE QUESTIONS AND ANSWERS
(VERIFIED ANSWERS) | EXAM PREP | COMPREHENSIVE EXAM
GUIDE 2026&2027
1. Which statement correctly describes the enthalpy change of combustion of a substance?
A. The enthalpy change when one mole of a substance is completely decomposed
B. The enthalpy change when one mole of a substance is completely burned in oxygen under
standard conditions
C. The energy required to break all bonds in one mole of a substance
D. The enthalpy change when one mole of a substance dissolves in water
Answer: B
The enthalpy change of combustion is the enthalpy change when one mole of a substance
undergoes complete combustion in oxygen under specified conditions.
2. A student measures the temperature rise when a known mass of ethanol is burned
beneath a copper calorimeter containing water. Which change would most directly reduce
heat loss to the surroundings?
A. Using a larger volume of water
B. Increasing the distance between the flame and calorimeter
C. Using a draught shield around the apparatus
D. Using a larger spirit burner
Answer: C
A draught shield reduces heat transfer from the flame and heated apparatus to the
surrounding air, improving the proportion of released energy transferred to the water.
3. Which equation represents the standard enthalpy change of formation of carbon
dioxide?
A. C(s) + O₂(g) → CO₂(g)
B. 2C(s) + O₂(g) → 2CO₂(g)
C. CO(g) + ½O₂(g) → CO₂(g)
D. C(s) + ½O₂(g) → CO(g)
Answer: A
,The standard enthalpy of formation is the enthalpy change when one mole of a compound is
formed from its elements in their standard states.
4. Why are bond enthalpy calculations described as approximate?
A. Bond enthalpies are measured only at very low temperatures
B. Bond enthalpies depend on the number of electrons in the atom
C. Bond enthalpies are calculated from ionic compounds only
D. Bond enthalpy values are mean values obtained from different compounds
Answer: D
Bond enthalpies are average values for a particular bond in different molecules, so they do
not represent the exact bond energy in every individual compound.
5. A reaction has a negative enthalpy change. Which statement is correct?
A. Energy is transferred from the surroundings to the reacting system
B. The products have greater enthalpy than the reactants
C. Energy is transferred from the reacting system to the surroundings
D. The reaction must have a negative activation energy
Answer: C
A negative enthalpy change indicates an exothermic reaction in which energy is released from
the reacting system to the surroundings.
6. Which expression can be used to calculate the heat energy transferred to water during a
calorimetry experiment?
A. q = mcΔT
B. q = mΔT/c
C. q = cΔT/m
D. q = mc/T
Answer: A
The heat transferred is calculated using q = mcΔT, where m is mass, c is specific heat capacity
and ΔT is temperature change.
,7. A student obtains a temperature increase of 8.4 °C when burning a fuel. The expected
temperature increase is 11.2 °C. What is the most likely explanation?
A. The fuel has no enthalpy change
B. Some heat was lost to the surroundings
C. The water absorbed no energy
D. The combustion was necessarily endothermic
Answer: B
Heat loss to the surroundings causes the measured temperature rise to be smaller than the
theoretical value, leading to an underestimated magnitude of enthalpy change.
8. Which change would make a bond enthalpy calculation more accurate?
A. Using ionic equations instead of molecular equations
B. Ignoring bonds in gaseous molecules
C. Using average bond enthalpy data appropriate to the bonds involved
D. Using only the strongest bond in each molecule
Answer: C
The calculation depends on correctly identifying every bond broken and formed and using
appropriate mean bond enthalpy values.
9. In an exothermic reaction, which statement about the energy profile is correct?
A. Products are at a lower energy level than reactants
B. Products are at a higher energy level than reactants
C. Reactants and products have identical energies
D. Activation energy is always zero
Answer: A
For an exothermic reaction, the products have lower enthalpy than the reactants because
energy has been released to the surroundings.
10. A student calculates an enthalpy change using a temperature increase that was
recorded to only one decimal place. Which quantity limits the precision of the final
answer?
A. The colour of the solution
B. The precision of the measured temperature change
, C. The atmospheric pressure only
D. The shape of the thermometer
Answer: B
The precision of experimental measurements affects the precision of the calculated enthalpy
change.
11. Which statement correctly describes dynamic equilibrium?
A. Reactants and products have equal concentrations
B. The forward reaction has stopped
C. The reverse reaction has stopped
D. Forward and reverse reactions occur at equal rates
Answer: D
At dynamic equilibrium, both reactions continue, but their rates are equal, so macroscopic
concentrations remain constant.
12. A reversible reaction reaches equilibrium in a sealed container. What happens if the
concentration of a reactant is increased?
A. The equilibrium constant increases
B. The equilibrium constant decreases
C. The equilibrium position may shift to oppose the change
D. Both reactions immediately stop
Answer: C
According to Le Chatelier's principle, increasing the concentration of a reactant causes the
equilibrium position to shift in the direction that reduces the added reactant.
13. Which statement about the equilibrium constant Kc is correct?
A. Its value changes when equilibrium concentrations change at constant temperature
B. Its value is fixed for a particular reaction at a specified temperature
C. It always has a value of 1 at equilibrium
D. It is unaffected by temperature
Answer: B
