# U(T,P) for Real Substances

**Real Substances**

:
Increasing T increases molecular vibrations, rotation and translation

Therefore, U increases as well.

Therefore, U increases as well.

Increasing P decreases U slightly at most values of T and P.

This phenomenon is due to complex molecular interactions.

This phenomenon is due to complex molecular interactions.

U = U(T, P)

U as a Function of T at Constant P

U

T

Internal energy is a strong function of temperature.

U as a Function of P at Constant T

U

P

Internal energy is a weak function of pressure at most T and P.

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