## Chemistry: The Central Science (13th Edition)

$\Delta H = -90.7kJ$
Use the Hess's law to find the $\Delta H$ 1. Reverse the first equation: $2 CO(g) --> 2 C (s) + O_2 (g): \Delta H = +221kJ$ $2 C(s) + O_2(g) + 4H_2 (g)--> 2CH_3OH(g): \Delta H -402.4kJ$ 2. Now, sum the equations: $2CO(g) + 2C(s) + O_2(g) + 4H_2(g) --> 2C(s) + O_2(g) + 2CH_3OH(g) : \Delta H = -181.4kJ$ *Remove the ones repeating. $2CO(g) + 4H_2(g) --> 2CH_3OH(g): \Delta H = -181.4kJ$ 3. Divide all the coefficients and the $\Delta H$ by 2: $CO(g) + 2H_2(g) --> CH_3OH(g): \Delta H = -90.7kJ$