If the standard state of sufur is S8 (s), which of the following equations represents the standard enthalpy of formation of H2SO4 (ℓ) ?
A. 2H (g) + S (g) + 4 O (g) H2SO4 (ℓ)
B. H2 (g) + S8 (g) + 2 O2 (g) H2SO4(ℓ)
C. H2SO4 (ℓ) H2 (g) + 1/8 S8 (s) + 2 O2 (g)
D. H2SO4 (ℓ) 2 H (g) + S (s) + 4 O (g)
E. H2 (g) + 1/8 S8 (s ) + 2 O2 (g) H2SO4(ℓ)
To determine the correct equation that represents the standard enthalpy of formation of H2SO4 (ℓ), we need to know the standard enthalpies of formation for the reactants and products involved. The standard enthalpy of formation is the change in enthalpy that occurs when one mole of a compound is formed from its elements in their standard states.
In this case, we can use standard enthalpies of formation from reference tables or databases. The standard enthalpy of formation of an element in its standard state is defined as zero. Therefore, the standard enthalpies of formation we need are as follows:
ΔH°f[H2SO4(ℓ)]: unknown
ΔH°f[H2(g)]: 0
ΔH°f[S8(s)]: 0
ΔH°f[O2(g)]: 0
Now, let's analyze each of the given equations and determine their enthalpies of formation:
A. 2H(g) + S(g) + 4O(g) → H2SO4(ℓ)
The enthalpy of formation of H2SO4(ℓ) in this equation is calculated as follows:
ΔH°f[H2SO4(ℓ)] = (2 * ΔH°f[H(g)]) + ΔH°f[S(g)] + (4 * ΔH°f[O(g)])
B. H2(g) + S8(g) + 2O2(g) → H2SO4(ℓ)
Using the same logic, the enthalpy of formation of H2SO4(ℓ) in this equation is calculated as:
ΔH°f[H2SO4(ℓ)] = ΔH°f[H2(g)] + ΔH°f[S8(g)] + (2 * ΔH°f[O2(g)])
C. H2SO4(ℓ) → H2(g) + (1/8)S8(s) + 2O2(g)
Here, the enthalpy of formation of H2SO4(ℓ) is:
ΔH°f[H2SO4(ℓ)] = ΔH°f[H2(g)] + [(1/8) * ΔH°f[S8(s)]] + (2 * ΔH°f[O2(g)])
D. H2SO4(ℓ) → 2H(g) + S(s) + 4O(g)
Similarly, the enthalpy of formation of H2SO4(ℓ) is calculated as:
ΔH°f[H2SO4(ℓ)] = (2 * ΔH°f[H(g)]) + ΔH°f[S(s)] + (4 * ΔH°f[O(g)])
E. H2(g) + (1/8)S8(s) + 2O2(g) → H2SO4(ℓ)
In this equation, the enthalpy of formation of H2SO4(ℓ) is:
ΔH°f[H2SO4(ℓ)] = ΔH°f[H2(g)] + [(1/8) * ΔH°f[S8(s)]] + (2 * ΔH°f[O2(g)])
To find the correct equation, compare the enthalpies of formation calculated above with the known standard enthalpy of formation for H2SO4(ℓ). The equation that balances out and matches the standard enthalpy of formation of H2SO4(ℓ) will be the correct one.