Free Thermochemistry and Energetics of Chemical Reactions MCQs with Answers

• A. Its value gives an idea about the relative stability of reactants and the products
• B. It is always negative
• C. Its value depends upon the nature of bonds
• D. Its value may be negative or positive

Explanation: The enthalpy of formation (ΔHf ) can be either negative (exothermic, for stable compounds) or positive (endothermic, for unstable…

• A. Enthalpy of reaction
• B. Enthalpy of formation
• C. Enthalpy of neutralization
• D. Enthalpy of combustion

Explanation: This equation shows the reaction of a strong acid (HCl) with a strong base (NaOH) to produce a salt (NaCl) and water.

• A. Formation of compound
• B. Combustion
• C. Dissolution of ionic compound
• D. Dilution of a solution

Explanation: Combustion is defined as a rapid reaction with an oxidant, usually oxygen, to produce heat and light.

• A. 84,000 J
• B. -2000/4.2 J
• C. 2000/4.2 J
• D. -8400 J

Explanation: Using the formula q = mcΔT, where ΔT = Tfinal - Tinitial = 5°C - 25°C = -20°C, q = (100 g)(4.2 J/g°C)(-20°C) = -8400 J.

• A. Glass calorimeter
• B. Bomb calorimeter
• C. Thermometer
• D. Manometer

Explanation: A bomb calorimeter is specifically designed for accurately measuring the heat of combustion.

• A. m x s
• B. c x ∆T
• C. s x ∆T
• D. c x s x ∆T

Explanation: In a bomb calorimeter experiment, the heat released by the reaction (q) is absorbed by the entire calorimeter assembly (bomb, water…

• A. Remains unaffected
• B. Increases
• C. Decreases
• D. All of these are possible

Explanation: A larger charge-to-size ratio means ions are more highly charged and more tightly packed, which increases the strength of ionic bonding in…

• A. Measurement of enthalpy change in a calorimeter
• B. Studying of first law of thermodynamics
• C. Born-Haber cycle
• D. Measurement of a heat of formation of a compound

Explanation: The Born-Haber cycle is a specific application of Hess's Law. It relates the lattice energy of an ionic compound (which cannot be measured…

• A. Enthalpy of combustion
• B. Lattice energy of covalent compounds
• C. Lattice energy of ionic compounds
• D. Enthalpy of ionization

Explanation: The Born-Haber cycle is a powerful theoretical tool used in chemistry to indirectly calculate the lattice energy of an ionic solid.

• A. ∆H° of the reaction depends on temperature
• B. ∆H° of reaction can be > or < zero
• C. ∆H° of catalyzed and uncatalyzed reaction is the same
• D. ∆H° is always < 0

Explanation: This statement is false. The standard enthalpy change (∆H°) can be positive for endothermic reactions (which absorb heat) or negative for…

• A. Spontaneous reaction
• B. Rate of reaction
• C. Heat of reaction
• D. Entropy of reaction

Explanation: Thermodynamics deals with the energy changes during chemical processes, especially the heat of reaction, enthalpy, entropy, and…

• A. 4180 J
• B. 8360 J
• C. 25080 J
• D. 50160 J

Explanation: Heat q = m × c × ΔT = 200 × 4.18 × (50.0 - 20.0) = 25080 J.

• A. Endothermic
• B. Exothermic
• C. Isothermic
• D. Adiabatic

Explanation: Exothermic reactions release heat, causing the surroundings to gain energy.

• A. -890.3 kJ
• B. -604.5 kJ
• C. -445.1 kJ
• D. -668 kJ

Explanation: ΔHrnx = ΣΔHf (products) - ΣΔHf (reactants) = [-393.5 + 2(-285.8)] - [-74.8] = -890.3 kJ.

• A. 16700 J
• B. 33400 J
• C. 41800 J
• D. 83600 J

Explanation: Heat = m × ΔHfus = 50.0 × 334 = 16700 J.

• A. -1124.8 kJ
• B. -562.4 kJ
• C. -206.4 kJ
• D. -1032.0 kJ

Explanation: ΔHrxn = [2(-285.8) + 2(-296.8)] - [2(-20.6)] = -1124.8 kJ.

• A. - 40 kJ/mol
• B. -50 kJ/mol
• C. - 45 kJ/mol
• D. - 6 kJ/mol

Explanation: The enthalpy of formation of a compound is the heat change that results when one mole of the compound is formed from its elements in their…

• A. ΔH°sol - The enthalpy change is the amount of heat absorbed or evolved when one mole of a substance is dissolved in excess solvent
• B. ΔH comb- The enthalpy change when one mole of a substance is burnt in excess air
• C. ΔH°at - The enthalpy change when one mole of gaseous atoms is formed from its compound under standard conditions
• D. ΔH°n - The enthalpy change when one mole of water is formed by the reaction of one mole of H⁺ ions from an acid with one mole of OH⁻ ions from a base

Explanation: The "enthalpy of atomization" is a thermodynamic quantity that represents the energy change associated with the process of breaking a…

• A. x
• B. x - y
• C. x + y
• D. y

Explanation: The difference in energy between products and reactants is x, and the activation energy for the reactants is y; therefore, in the reverse…

• A. The reaction proceeds in the forward direction at 300 K
• B. At 1200 K, the reaction proceeds in the reverse direction
• C. At 300 K, Kp > 1
• D. At 300 K, the products will be favored more than reactants at equilibrium

Explanation: The correct answer is Option C because at 300 K; Kp > 1. In an exothermic reaction, decreasing the temperature shifts the equilibrium…