Enthalpy problem?

Question

what is delta E (internal energy) for the formation of 1 mole of CO at 1 atm and 25 C.

C(graphite) + 1/2 O2 (g) ----> CO(g) delta H = -110.5 kj/mol

delta E = delta H - RT(delta n)

delta n = number of moles of products - number of moles of reactants

i did this problem and get an answer of 109 kj, but the answer is wrong. its supposed to be 111. does someone know why?

Answer 1

delta E = delta H - RT(delta n)

delta E = -110.5 kj - (8.314 e-3)(298)(0.5)

delta E = -110.5 kj - (1.2)

dE = -111.5 kJ

did you use the "-" 110.5kJ & the "-" RTdn

did your

delta n = moles of products - moles of reactants

use the moles of solid carbon, which you can't do...

because the RTdn uses the dn of gases only