# Thermodynamics problems and solutions

When solving a Physics problem in general and one of Thermodynamics in particular, it is important to follow a certain order. Get used to being organized when you solve problems, and you will see how it gives good results. It is worth spending a little time on the previous analysis of a problem before you tackle it.

The solved thermodynamic problems shown in these pages make use of these three concepts: workheat and internal energy to a closed system, generally an ideal gas. These three concepts are related through the First Law of Thermodynamics. We will use the so-called Clausius convention to express the first law: the work is done by the thermodynamic system on its surroundings. In addition, the sign convention that we will use is the following one:

Sign convention

• The work done by a gas on its surroundings is positive when it expands. When the gas compresses, the work is negative.
• The heat absorbed by a system is positive. The heat supplied by a system to its surroundings is negative.

In addition, we will always use the SI units.

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When solving a Thermodynamic problem, follow the following steps:

• Read carefully the Problem Statement..
• Draw a picture of the physical situation depicted in the problem statement.
• Write in your notebook the givens in the problem statement.
• Identify the equations that you will have to use to solve the problem.
• Be careful with the signs for the heat, the work and the internal energy variation.
• Do not forget to include the units in your results.
• Review the problem and check that the results you have obtained make sense.

Consult the summary table to see how to calculate the work, the heat exchanged and the change in the internal energy for the four main reversible processes of an ideal gas.

On the following pages you will find solved Thermodynamic problems. Try to do them yourself before looking at the resolution.

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