Question

using bond energies calculate the of formation of dimethyl ether from its element from the reaction below (c(s) to c(g) = 720kj) 2c 9g)+3H2 (g)+1/2 02 (g) H3C-0- CH3(g)

Answer 1

$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)