"2C(g)+3H_2(g)+1\/2O_2(g) \\to CH_3-O-CH_3""(g)"
As 1 mole of dimethyl ether is formed; "\\Delta H_{rxn}=\\Delta H_f"
"\\Delta H_f=\\Delta H_{f(products)}-\\Delta H_{f(reactants)}"
"\\Delta H_{f(products)}=6*(C-H bond energy)+" "2*(C-O bond energy)"
"=6*413+2*358"
"=3194kJ"
"\\Delta H_{f(reactants)}=2*\\Delta H_{f(Carbon)}+0+0" (as oxygen and hydrogen are in elemental states)
"=2*720"
"=1440kJ"
"\\Delta H_f=3194-1440"
"=1754kJ" (Answer)
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