Enthalpy and Pressure

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

Enthalpy and Pressure

Postby 705279989 » Wed Jan 22, 2020 3:59 pm

Why does enthalpy have to be at a constant pressure?

Mariah
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Re: Enthalpy and Pressure

Postby Mariah » Wed Jan 22, 2020 4:09 pm

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

Postby 805303639 » Thu Jan 23, 2020 8:45 pm

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

Postby Miriam Villarreal 1J » Fri Jan 24, 2020 3:10 pm

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
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Re: Enthalpy and Pressure

Postby 705302428 » Fri Jan 24, 2020 7:14 pm

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


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