Final answer:
The Joule-Thomson coefficient is defined as (dH/dT)_P. It determines whether a gas will cool or heat up when it expands or contracts.
Step-by-step explanation:
The Joule-Thomson coefficient is defined as (dH/dT)_P.
When a gas is allowed to expand or contract without performing any work, the change in enthalpy (H) with respect to temperature (T) at constant pressure (P) is known as the Joule-Thomson coefficient. It is used to determine whether a gas will cool or heat up when it expands or contracts.
For example, if the Joule-Thomson coefficient is positive, the gas will cool down when it expands, while if it is negative, the gas will heat up.