# Thermodynamics

## Vocabulary

### absolute zero

minimum possible temperature theoretically achievable, equal to 0 K (–273.15°C), at which there is no particle motion

### entropy (S)

measure of the disorder of a system

### equilibrium

state in which the forward and reverse reactions are equal

### first law of thermodynamics

law that states that energy cannot be created or destroyed, only transformed from one type of energy to another type of energy; given as $\Delta U=q+w$

### free energy

capacity of a system to do work

### Gibbs free energy (G)

amount of work done by a system, expressed as $G=H-TS$, where H is enthalpy, T is temperature, and S is entropy

### macrostate

measurable macroscopic properties of a system

### microstate

possible energy and positional configuration of the particles of a system

### nonspontaneous change

process in which energy must be added to the system for the change to occur

### second law of thermodynamics

law that states that the total entropy of an isolated system only increases over time

### spontaneous change

process in which energy is released as a system changes

### standard entropy (S°)

entropy of one mole of a substance under standard state conditions, expressed in units J/(K mol)

### standard state

set of specific conditions under which reactions are measured, typically 0°C and 1 atm pressure

### thermodynamics

branch of physical science that investigates the energy and work of systems

### third law of thermodynamics

law that states that the total entropy of a system approaches zero as the temperature of the system approaches absolute zero

### work (w)

energy that is transferred when a force acts on an object over a distance

### zeroth law of thermodynamics

law that states that when two thermodynamic systems are in thermal equilibrium with a third system, they are in thermal equilibrium with each other