### Homework 8.93b

Posted:

**Wed Jan 17, 2018 2:51 pm**(a) Calculate the work that must be done against the atmosphere for the expansion of the gaseous products in the combustion of 1.00 mol C6H6(l) at 25 C and 1.00 bar.

(b) Using data in Appendix 2A, calculate the standard enthalpy of the reaction. (c) Calculate the change in internal energy, U , of the system.

The equation I wrote for this problem is 2C

In part (a) of 8.93, I got the correct answer by assuming that H2O was produced in gas form, but when I tried part (b) using the enthalpies of formation method I got the wrong answer. I replaced the enthalpy of formation for H

(b) Using data in Appendix 2A, calculate the standard enthalpy of the reaction. (c) Calculate the change in internal energy, U , of the system.

The equation I wrote for this problem is 2C

_{2}H_{6}(g)+ 15O_{2}(g) → 12CO_{2}(g) + 6H_{2}O(g).In part (a) of 8.93, I got the correct answer by assuming that H2O was produced in gas form, but when I tried part (b) using the enthalpies of formation method I got the wrong answer. I replaced the enthalpy of formation for H

_{2}O(g) with the enthalpy of formation for H_{2}O(l) and then got the correct answer. Why does part (b) assume the H_{2}O is liquid rather than gas? Thank you!