SCH4U UNIT 2 EXAM WITH 150+ REALISTIC PRACTICE QUESTIONS & DETAILED RATIONALES (THERMOCHEMISTRY & KINETICS & EQUILIBRIUM)

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SCH4U Unit 2,3,4 and 5 Chem Test |

Questions and Answers Latest Updated

2026 (Graded A+)-OVS

Question 1 (MC)

Which of the following is a correct definition of enthalpy (H)?

A. The total kinetic energy of particles in a system

B. The heat content of a system at constant pressure

C. The internal energy plus pressure-volume work (H = U + PV)

D. Both B and C




Answer: D. Both B and C

Rationale: Enthalpy (H) is defined as the internal energy (U) plus

the product of pressure and volume (PV). Under constant

pressure, the change in enthalpy (ΔH) equals the heat absorbed

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or released by the system. This is why enthalpy is often called

the "heat content" at constant pressure. Options B and C are both

correct and complementary definitions.

Question 2 (MC)

The symbol ΔH°f represents:

A. Standard enthalpy change of reaction

B. Standard enthalpy change of formation

C. Standard enthalpy change of combustion

D. Standard enthalpy change of fusion




Answer: B. Standard enthalpy change of formation

Rationale: ΔH°f denotes the standard enthalpy change when

one mole of a compound is formed from its elements in their

standard states under standard conditions (usually 25°C and 1

bar). ΔH°rxn (A) is for any reaction; ΔH°comb (C) is for

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combustion; ΔH°fus (D) is for melting. Standard formation

enthalpies are used to calculate reaction enthalpies via Hess's

law: ΔH°rxn = Σ ΔH°f(products) – Σ ΔH°f(reactants).

Question 3 (T/F)

An exothermic reaction has a positive ΔH.




Answer: False

Rationale: Exothermic reactions release heat to the surroundings,

so the enthalpy of the products is lower than the enthalpy of the

reactants. Therefore ΔH = H_products – H_reactants is negative.

Endothermic reactions have positive ΔH. This sign convention is

important for energy diagrams and calculations.

Question 4 (FIB)

The SI unit for enthalpy change is the ________.

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Answer: joule (J) or kilojoule (kJ)

Rationale: Enthalpy changes are measured in joules (J) or

kilojoules (kJ). Molar enthalpy changes are reported in kJ/mol.

Calories (cal) are also used in some contexts, but the SI unit is the

joule. 1 cal = 4.184 J. In thermochemistry, energy is often

expressed in kJ or kJ/mol.

Question 5 (MC)

Given the thermochemical equation: 2H₂(g) + O₂(g) → 2H₂O(l)

ΔH = –572 kJ. What is the enthalpy change for the formation of

one mole of water?

A. –572 kJ

B. –286 kJ

C. +286 kJ

D. +572 kJ