با استفاده از دادههای زیر، مقدار $\Delta H$ واکنش $C{{S}_{۲}}(l)+۶{{H}_{۲}}{{O}_{۲}}(l)\to C{{O}_{۲}}(g)+۶{{H}_{۲}}O(l)+۲S{{O}_{۲}}(g)$ برحسب کیلوژول کدام است؟ $C{{O}_{۲}}(g)+۲S{{O}_{۲}}(g)\to C{{S}_{۲}}(l)+۳{{O}_{۲}}(g)\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\Delta H=۱۰۷۷kJ$ ${{H}_{۲}}(g)+{{O}_{۲}}(g)\to {{H}_{۲}}{{O}_{۲}}(l)\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\Delta H=-۱۸۸kJ$ ${{H}_{۲}}(g)+\frac{۱}{۲}{{O}_{۲}}(g)\to {{H}_{۲}}O(l)\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\Delta H=-۲۸۶kJ$
واكنش اول را معكوس میكنيم. واكنش دوم را معكوس كرده و در 6 ضرب میكنيم و واكنش سوم را در عدد 6 ضرب میكنيم. در انتها همۀ واکنشها و $\Delta H$های آنها را با هم جمع میکنیم. $C{{S}_{2}}(l)+3{{O}_{2}}(g)\to C{{O}_{2}}(g)+2S{{O}_{2}}(g)\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\Delta H=-1077kJ$ $6{{H}_{2}}{{O}_{2}}(l)\to 6{{H}_{2}}(g)+6{{O}_{2}}(g)\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\Delta H=188\times 6=1128kJ$ $6{{H}_{2}}(g)+3{{O}_{2}}(g)\to 6{{H}_{2}}O(l)\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\Delta H=-286\times 6=-1716kJ$ $C{{S}_{2}}(l)+6{{H}_{2}}{{O}_{2}}(l)\to C{{O}_{2}}(g)+6{{H}_{2}}O(l)+2S{{O}_{2}}(g)\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\Delta H=-1077+1128-1716=-1665kJ$