Free System, Surroundings and State Functions MCQs with Answers

1. In thermodynamics, the system is defined as

• A. everything in the universe
• B. the container only
• C. the energy of the reaction
• D. the part of the universe under study, separated from the surroundings by a boundary

Explanation: The system is whatever the chemist chooses to study, usually the reacting substances, and everything else is the surroundings, with the boundary between them being real or imaginary. An isolated system exchanges neither matter nor energy, a closed system exchanges energy only and an open system exchanges both. A reaction in an open beaker is therefore an open system.

2. A state function is a property whose value depends on

• A. the path taken to reach the present state
• B. the present state of the system only, not on how it was reached
• C. the time taken for the change
• D. the catalyst used

Explanation: Enthalpy, internal energy, entropy, pressure, volume and temperature are all state functions, so the change in any of them depends only on the initial and final states. This path independence is precisely what makes Hess's law valid and useful. Work and heat, by contrast, are path functions, since their values do depend on how the change was carried out.

3. Which of the following is NOT a state function?

• A. Enthalpy
• B. Internal energy
• C. Work
• D. Temperature

Explanation: The amount of work done in going from one state to another depends on the route taken, for example whether a gas expands quickly or slowly, so work is a path function. Enthalpy, internal energy and temperature depend only on the current condition of the system. Heat is the other common path function, which is why heat and work are written as small quantities rather than as changes in a property.