## Chemistry (4th Edition)

The reactants in the first reaction is the products of the second reaction and the products of the first reaction is the reactants in the second reaction. That is, the first reaction is reversed to get the second reaction. When the first reaction is reversed to get the second reaction, we need to change the sign of $\Delta H$ for the first reaction to get the $\Delta H$ corresponding to the second reaction. As $\Delta H$ for the first reaction is -595.8 kJ/mol, $\Delta H$ for the second reaction= +595.8 kJ/mol