## Enthalpy and Pressure

705279989
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Joined: Mon Jun 17, 2019 7:24 am

### Enthalpy and Pressure

Why does enthalpy have to be at a constant pressure?

Mariah
Posts: 104
Joined: Fri Aug 02, 2019 12:16 am

### Re: Enthalpy and Pressure

IT has to be measured at a constant pressure because as pressure increases, so does enthalpy.

805303639
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### Re: Enthalpy and Pressure

The equation deltaH = deltaE + delta(PV) describes the change in enthalpy of a system. We need not measure the enthalpy at constant pressure per se but doing so simplifies the equation to deltaH = q (after some algebra). As a result, we know the heat (q) released or absorbed in the reaction equals the change in the system's enthalpy (deltaH).

Miriam Villarreal 1J
Posts: 105
Joined: Sat Aug 17, 2019 12:16 am

### Re: Enthalpy and Pressure

Most chemical reactions occur at constant pressure, so enthalpy is more often used to measure heats of reaction given off or absorbed during a chemical reaction at constant pressure.
However The heat given off or absorbed when a reaction is run at constant volume is equal to the change in the internal energy of the system

705302428
Posts: 50
Joined: Sat Aug 24, 2019 12:16 am

### Re: Enthalpy and Pressure

Pressure and enthalpy are directly proportional so pressure needs to be constant in order to properly measure enthalpy.