Which of the following statements is (are) true? a) When a...

Which of the following statements is (are) true? a) When a system does work, its internal energy always decreases. b) Work done on a system always decreases its internal energy. c) When a system does work on its surroundings, the sign of the work is always positive. d) Positive work done on a system is always equal to the system's gain in internal energy. e) If you push on the piston of a gas-filled cylinder, the energy of the gas in the cylinder will increase.

Which of the following statements is (are) true?
a) When a system does work, its internal energy always decreases.
b) Work done on a system always decreases its internal
energy.
c) When a system does work on its surroundings, the sign of the work is always positive.
d) Positive work done on a system is always equal to the system's gain in internal energy.
e) If you push on the piston of a gas-filled cylinder, the energy of the gas in the cylinder will increase.

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Key Concepts

Sign Conventions

Sign conventions in thermodynamics are crucial for correctly applying the First Law. The standard convention assigns a positive sign to heat added to the system and to work done on the system, while work done by the system is considered negative. This ensures consistency when calculating the energy changes during various thermodynamic processes.

First Law of Thermodynamics

The First Law of Thermodynamics is a statement of energy conservation that relates changes in internal energy to the heat exchanged and the work performed by or on the system. It is expressed as ?U = Q - W, where ?U is the change in internal energy, Q is the heat added to the system, and W is the work done by the system.

Internal Energy

Internal energy is the total energy contained within a system, including kinetic and potential energies at the molecular level. It is a state function, meaning its value depends only on the current state of the system and not on the path taken to reach that state.

Work in Thermodynamics

Work in thermodynamics refers to the energy transfer that occurs when a force is applied over a distance, such as the expansion or compression of a gas. The sign of work depends on the convention used: typically, work done by the system on its surroundings is considered negative, while work done on the system is considered positive.

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