A scientist measures the standard enthalpy change for the following reaction to be 67.9 kJ: Fe2O3(s) + 3 H2(
92Fe(s) + 3 H2O(9)
Based on this value and the standard enthalpies of formation for the other substances, the standard enthalpy of formation
of H2O(g) is
kJ/mol.

The standard enthalpy of formation  of is  -252.1 kJ/mol.

Explanation:

The balanced chemical reaction is,

The expression for enthalpy change is,

Putting the values we get :

Thus standard enthalpy of formation  of is  -252.1 kJ/mol.

percent abundance for cu-63 can be shown as:

63 x + 65 (1-x) = 62.9296

65 - 62.9296 = 2 x

x = 1.035

thus, percent abundance for cu-63 is 1.035

percent abundance for cu-65 can be shown as:

63 x + 65 (1-x) = 64.9278

65 - 64.9278 = 2 x

x = 0.0361

thus, percent abundance for cu-63 is 0.0361

the mass spectrum of cu-63 showing the intense peak as, this isotope is found in nature more abundantly around 92.38 % in comparison to cu-65 which is found 62.58 % naturally