Calculate ΔHo for the chemical reaction:

[AMan24]

Homework Statement

Homework Equations

The Attempt at a Solution

2(255) - [(1)(159) + (1)(243)]
= +108KJ

The answer key says its b) -108KJ. Am i doing something wrong or is the book wrong?

 

[MexChemE]

When using bond enthalpies, the way you calculate the heat of reaction is
$$\Delta H° = \sum \Delta H_{\textrm{Broken}} - \sum \Delta H_{\textrm{Formed}}$$
As in, "the sum of enthalpy changes by broken bonds minus the sum of enthalpy changes by formed bonds." So, the correct answer is -108 kJ.

 

[Borek]

ΔH° is not the same thing as a bond enthalpy. Quite the opposite - positive bond enthalpy means negative ΔH° (think why).