Question

Consider the following reaction CaSO4 (s) ------- Ca +2 (aq) + SO4 -2 (aq)

A. Calculate delta H

B. Calculate delta S

C. Calculate delta G at 25 C

Answer 1

CaSO₄ (s) Ca ⁺² (aq) + SO₄^-2 (aq) ; ΔH = ?

(A)ΔH = ΔH⁰_fproducts – ΔH⁰_freactants

ΔH = [ ΔH⁰_fCa2+(aq) )+ ( ΔH⁰_{fSO4 ^-2 (aq)} )]- [ΔH⁰_{fCaSO4 (s)} ]

    = [(-542.83)+(-909.27)] - [‐1425.2] kJ/mol

    = -26.9 kJ/mol

    = -26.9x10³ J/mol

(B) CaSO₄ (s) Ca ⁺² (aq) + SO₄^-2 (aq) ; ΔS = ?

ΔS = ΔS⁰_fproducts – ΔS⁰_freactants

ΔS = [ ΔS⁰_fCa2+(aq) )+ ( ΔS⁰_{fSO4 ^-2 (aq)} )]- [ΔS⁰_{fCaSO4 (s)} ]

    = [(-53.14)+(20.08)] - [108.37] J/mol

    = -141.43 J/mol

(C) ΔG = ΔH - TΔS     Where T = temperature = 25+273=298K

           = (-26.9x10³) - (298x(-141.43))

           = 15.246x10³ J

           = 15.246 kJ