Question

Consider the following thermochemical equations. Cu_2O(s) + 1/2 O_2(g) rightarrow 2CuO(s) Delta H degree = - 144 kJ Cu_2O(s) rightarrow Cu(s) +CuO(s) Delta H degree = +11 kJ Calculate the standard enthalpy of formation of CuO(s). a) - 166 kJ b) - 299 kJ c) +299 kJ d) +155 kJ e) -155 kJ

Please Answer and explain. thanks

Answer 1

Given that

Cu₂O (s) + 1/2 O2 gives 2CuO   $\Delta$H = -144 kJ equation 1

Cu₂O (s) gives Cu + CuO $\Delta$H = 11 kJ equation 2

reverse the direction (note: while reversing the direction of a reaction the sign of $\Delta$H will change)

Cu + CuO gives Cu₂O (s) $\Delta$H = -11 kJ equation 3

add equation 3 with equation 1

Cu₂O (s) + 1/2 O2 + Cu + CuO gives Cu₂O (s) + 2CuO   $\Delta$H = -155 kJ

cancel the similar terms on both side of the eqaution

then

1/2 O2 + Cu gives CuO $\Delta$H = -155 kJ

option e is the correct answer.