# Enthalpy = internal energy+pressure*volume

1. Apr 17, 2005

### sid_galt

My chem book says that

Enthalpy = internal energy+pressure*volume

However it says that enthalpy for a particular state cannot be calculated. Only the enthalpy change can be calculated. This has me confused.
Aren't internal energy, pressure and volume calculabe for a particular state? Then why can't we calculate absolute enthalpy?

2. Apr 17, 2005

### The Bob

Enthaply is used to calculate how much energy is taken in or released by a reaction where bonds have been broken (well all reactions really need bonds to brake but still...).

Enthaply, however, also depends on the temperature (if I am correct) and ,thus, it is only possible to have an equation for the change.

This might help or checking the rest of these might as well.

It should be change in PV, or $$\Delta PV$$, the work in expansion against the atmosphere