# Reaction enthalpy at non-standard conditions

I am tutoring a pupil in high-school out of necessity (no other teachers avail), while I am not so acquainted anymore with chemistry. The pupil showed me a question concerning the calculation of the reaction enthalpy which looked somewhat as follows:

**1. Problem statement, all variables and given/known data**

Calculate the reaction-enthalpy for the reaction:

[itex]C_3H_8 (g) + 5O_2 (g) \rightarrow 3CO_2 (g) + 4H_2O (g)[/itex]

at 30[itex]^\mathrm{o}[/itex]C and 1.08 atm.

The formation enthalpies at standard conditions and the heat capacities at constant pressure were known.

**2. Relevant equations**

**3. The attempt at a solution**

NOTE: I am not sure anymore about the exact reaction or the exact temperature and pressure, the above is meant as a generic example of the exercise that the pupil showed me.

As I remember, first the formation enthalpies at the non-standard conditions should be computed. This should be done in two steps:

1) Take into account the increase in temperature assuming constant pressure: use [itex]\Delta H = C_p\Delta T[/itex].

2) Take into account the increase in pressure assuming constant temperature.

I cannot remember how the second step should be computed, neither did I find some appropriate formula during a quick search.

Is the current approach the correct one? Could it be possible to give me some more information about how to proceed?

Thanks in advance

Giorgos

http://ift.tt/1hkdBem

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