1. Work, Heat, and Changes in Internal Energy

1. Work, Heat, and Changes in Internal Energy

Concept Explanation:

In thermodynamics, internal energy refers to the total energy contained within a system, which includes both the kinetic energy and potential energy of its particles. Changes in a system's internal energy can occur through two main processes: work and heat.

• Work (W): Work is the energy transfer that occurs when a force is applied to a system, causing displacement. In a thermodynamic context, work is often associated with the expansion or compression of gases. When a gas expands, it does work on its surroundings; when it is compressed, work is done on the gas.

• Heat (Q): Heat is the energy transfer between a system and its surroundings due to a temperature difference. Heat flows naturally from a hotter object to a cooler one until thermal equilibrium is achieved.

The relationship between work, heat, and the change in internal energy of a system is governed by the first law of thermodynamics, which we will explore in the next section.

Example Problem:

A gas in a cylinder is compressed, performing 100 J of work on the gas. During this process, 150 J of heat is transferred from the surroundings to the gas. What is the change in the internal energy of the gas?

Solution:

The change in internal energy (ΔU) is given by the first law of thermodynamics:

ΔU = Q + W

Substituting the given values:

ΔU = 150 J + 100 J = 250 J

So, the internal energy of the gas increases by 250 J.