# Thermodynamics

## Overview

### Description

Thermodynamics is the branch of science that deals with the energy and work, the energy transferred when a force acts on an object, of systems. Every chemical reaction can be considered a system. Chemical reactions that release energy are spontaneous changes, while those that require energy in order to proceed are nonspontaneous changes. Changes in energy of a system cause changes in entropy, the measurement of the disorder of a system. Four laws describe thermodynamics. The zeroth law states that when two systems are in thermal equilibrium with a third system, they are in thermal equilibrium with each other. The first law states that the total energy of an isolated system is constant. The second law, also called the law of conservation of energy, states that total entropy of an isolated system only increases over time. The third law states that the total entropy of a system approaches a constant value as the temperature of the system approaches absolute zero, which is the minimum temperature theoretically possible. Free energy, the capacity of a system to do work, determines whether a reaction is spontaneous or nonspontaneous.

### At A Glance

• Thermodynamics is the branch of science that deals with the study of the energy and work of systems. Chemical processes are governed by the laws of thermodynamics.
• Processes can be described as either spontaneous or nonspontaneous. Spontaneous processes are those that give off free energy when they occur and result in lower energy processes. Nonspontaneous processes require an input of energy to occur.
• Entropy is a measurement of the disorder of a system. A system with greater disorder has a greater possible variety of energy distributions.
• The zeroth law of thermodynamics states that when two systems are in thermal equilibrium with a third system, they are in thermal equilibrium with each other. The first law of thermodynamics states that the total energy of a system is constant.
• The second law of thermodynamics states that total entropy of an isolated system only increases over time.
• The third law of thermodynamics states that the total entropy of a system approaches a constant value as the temperature of the system approaches absolute zero.
• Free energy, which is the capacity of a system to do work, can be used to determine whether a reaction is spontaneous or nonspontaneous under given conditions.