-130KJ is the standard heat of formation of CuO.
Explanation:
The standard heat of formation or enthalpy change can be calculated by using the formula:
standard heat of formation of reaction = standard enthalpy of formation of product - sum of enthalpy of product formation
Data given:
Cu2O(s) ---> CuO(s) + Cu(s) ∆H° = 11.3 kJ
2 Cu2O(s) + O2(g) ---> 4 CuO(s) ∆H° = -287.9 kJ
CuO + Cu ⇒ Cu2O (-11.3 KJ) ( Formation of Cu2O)
When 1 mole Cu20 undergoes combustion 1/2 moles of oxygen is consumed.
Cu20 + 1/2 02 ⇒ 2CuO (I/2 of 238.7 KJ) or 119.35 KJ
So standard heat of formation of formation of Cu0 as:
Cu + 1/2 02 ⇒ CuO
putting the values in the equation
ΔHf = ΔH1 + ΔH2 (ΔH1 + ΔH2 enthalapy of reactants)
heat of formation = -11.3 + (-119.35)
= - 130.65kJ
-130.65 KJ is the heat of formation of CuO in the given reaction.
The standard heat of formation of CuO is -310.5 kJ.
Explanation:
To get the standard heat of formation, we have to multiply the second equation by 2 and reverse it and add it to the first equation, we will get the required compound.
2 Cu₂O(s) + O₂(g) → 4 CuO(s) ∆H° = -287.9 kJ ------ 1
Cu₂O(s) → CuO(s) + Cu(s) ∆H° = 11.3 kJ ------ 2
Now multiplying the equation 2 by 2 and reversing it, we will get,
2 CuO(s) + 2 Cu(s) → 2 Cu₂O(s) ∆H° = -22.6 kJ ----- 3
Now adding eq. 3 with eq. 1 we will get the formation of CuO as,
2 Cu(s) + O₂(g) → 2 CuO(s) ∆H° = -22.6 kJ - 287.9 kJ = -310.5 kJ
