8.67

[Rakhi Ratanjee 1D]

For the reaction 1H2+(1/2)O2--> 1H2O(liquid), the final calculation of the bond enthalpies comes to 242kJ/mol. From the tables in the textbook, the answer would work out to be a +242kJ/mol, but the solutions manual states that it is negative. Why?
Also, why do you have subtract 44 kJ/mol to get the final answer?

[sahajgill]

I did this question by using the bond enthalpies. The total enthalpy required to break the bonds was 684 kj.mol^-1 but the total enthalpy of the formation of the bonds was -926 kj.mol^-1 and is negative since when bonds form, it is an exothermic process. Add -926 to 684 and you get -242 kj.mol^-1

[Rakhi Ratanjee 1D]

In 8.67 part B, the desired reaction is C(gr)+2H2(g)+(1/2)O2(g) --> CH3OH(l)
What is C(gr)?

[Rakhi Ratanjee 1D]

C(gr) just means that the natural form of carbon is in solid graphite.