The molar heat of reaction, H rxn, for the reaction of

Ca(s) + 2H+(aq) Ca2+(aq) + H2(g)
is -544.789 kJ/mol
and Hrxn, for the reaction of
CaO(s) + 2H+(aq) Ca2+(aq) + H2O(l)
is -192.42 kJ/mol,
the heat of formation of water is -286 kJ/mol,

The H ffor CaO(s) is _____ kJ/mol.

Thank you!

637.58

-637.58

To find the heat of formation (ΔHf) for CaO(s), we can use the concept of Hess's law and the given data.

Hess's law states that:

"The enthalpy change for a reaction is the same, regardless of whether it occurs in one step or a series of steps."

We can apply this principle to find the heat of formation (ΔHf) for CaO(s) by manipulating the given equations.

1. First, let's reverse the second equation to reflect the formation of CaO(s):

Ca2+(aq) + H2O(l) → CaO(s) + 2H+(aq)

2. Now, since the enthalpy change for the reverse reaction is the negative of the original equation, the enthalpy change for the reverse reaction is +192.42 kJ/mol.

3. We need to balance the reverse reaction, so we multiply the equation by 1/2:

(1/2) Ca2+(aq) + (1/2) H2O(l) → (1/2) CaO(s) + H+(aq)

4. Now, we can compare the reversed and balanced equation to the formation equation of CaO(s):

(1/2) CaO(s) + H+(aq) → (1/2) CaO(s) + H2O(l)

The coefficient of CaO(s) in both equations is the same (1/2). Therefore, the heat of formation (ΔHf) for CaO(s) can be obtained by taking the difference between the enthalpy change of the two equations:

ΔHf for CaO(s) = ΔH of formation equation - ΔH of reversed equation
= -192.42 kJ/mol - (-544.789 kJ/mol)
= -192.42 kJ/mol + 544.789 kJ/mol
= 352.369 kJ/mol

Therefore, the heat of formation (ΔHf) for CaO(s) is +352.369 kJ/mol.