Thermodynamics and Enthalpy - Exam Prep Problem Set

Thermodynamics and Enthalpy - Problem Set

Q. In an isothermal process, which of the following statements is true?

Solution

In an isothermal process, the temperature remains constant, which means the internal energy of an ideal gas does not change.

Correct Answer: A — The temperature remains constant.

Q. What is the change in enthalpy (ΔH) for the reaction: H2(g) + 1/2 O2(g) → H2O(l) if the standard enthalpy of formation of H2O(l) is -285.8 kJ/mol?

Solution

The change in enthalpy for the reaction is equal to the standard enthalpy of formation of H2O(l), which is -285.8 kJ/mol.

Correct Answer: A — -285.8 kJ/mol

Q. What is the enthalpy change (ΔH) for the reaction: 2H2(g) + O2(g) → 2H2O(g) if ΔHf for H2O(g) is -241.8 kJ/mol?

Solution

The enthalpy change for the reaction is 2 times the standard enthalpy of formation of H2O(g), which is -241.8 kJ/mol, giving -483.6 kJ.

Correct Answer: A — -483.6 kJ

Q. What is the enthalpy change for the reaction: N2(g) + 3H2(g) → 2NH3(g) if the standard enthalpy of formation of NH3(g) is -45.9 kJ/mol?

Solution

The enthalpy change for the reaction is 2 times the standard enthalpy of formation of NH3(g), which is -45.9 kJ/mol, giving -91.8 kJ.

Correct Answer: A — -91.8 kJ

Q. What is the standard enthalpy change for the combustion of methane (CH4) if ΔHf for CO2(g) is -393.5 kJ/mol and for H2O(l) is -285.8 kJ/mol?

Solution

The standard enthalpy change for the combustion of CH4 is calculated as ΔH = [2(-393.5) + (-285.8)] - [1(0)] = -890.3 kJ/mol.

Correct Answer: A — -890.3 kJ/mol

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