The standard enthalpy of formation (Δ[tex]H_f[/tex]) is a measure of the energy released or consumed when one mole of a substance is created under standard conditions from its pure elements.
Standard enthalpies (Δ[tex]H_f[/tex]) of formation for given reaction is 978.3 kJ
The standard enthalpy of formation is defined as the enthalpy change when one mole of a substance in the standard state (1 atm of pressure and 298.15 K) is formed from its pure elements under the same conditions.
Given reaction ;
[tex]N_2O_4(g) + 4H_2 (g) - > N_2(g) + 4H_2O(g)[/tex]
To Find : Δ[tex]H_f[/tex]
Δ[tex]H_f[/tex] = ∑np Δ[tex]H_f[/tex] (products) – ∑np Δ[tex]H_f[/tex] (reactants)
Δ[tex]H_f[/tex] = [1(Δ[tex]H_f[/tex] [tex]N_2[/tex]) + 4(Δ[tex]H_f[/tex] [tex]H_2O[/tex])] – [1(Δ[tex]H_f[/tex] [tex]N_2O_4[/tex]) + 4(Δ[tex]H_f[/tex] [tex]H_2[/tex])]
Δ[tex]H_f[/tex] = [1(0) + 4(-241.8)] – [1(+9.16) + 4(0)]
Δ[tex]H_f[/tex] = [4(-241.8)] – [1(+9.16)] = 978.3 kJ
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