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

$\Delta H = -1300kJ$
Using the Hess's law: $P_4 (s) + 3 O_2(g) --> P_4O_6(s) : \Delta H = -1640.1kJ$ $P_4 (s) + 5 O_2(g) --> P_4O_{10}(s) : \Delta H = -2940.1kJ$ 1. Reverse the first equation. $P_4O_6(s) --> P_4 (s) + 3 O_2(g) : \Delta H = +1640.1kJ$ $P_4 (s) + 5 O_2(g) --> P_4O_{10}(s) : \Delta H = -2940.1kJ$ 2. Now, sum the equations: $P_4 (s) + 5 O_2(g) + P_4O_6(s) --> P_4O_{10}(s) + P_4 (s) + 3 O_2(g) : \Delta H = -1300kJ$ *1640.1 - 2940.1 = -1300 $2 O_2(g) + P_4O_6(s) --> P_4O_{10}(s) : \Delta H = -1300kJ$