Question

7 Coleulate Kt Given the following data: 4. (Equation 1) S(s) +3/202(g) - SO3(g) AG= - 371 kJ slsb to gts2 gniwollot od lo do09 rw onimtsbThan 24 HA To (Equation 2) 2SO2(g)+ O2(g)2 SO3(g) AG°= - 142 kJ SO2(g) Calculate AG° for the goal equation S(s) +O2(g) 008 Is this reaction spontaneous? 00 02T 00 noitons gaivollot slt To doc9 10l 2410

Answer 1

Step 1: Explanation:

Note:  

• if a chemical reaction is reversed then the sign of the ΔG⁰ of the reaction reverses
• if a chemical reaction is multiply by any number  then the ΔG⁰  is also multiply by that same number

Step 2: write all the reactions

S(s) + 3/2 O₂(g) ------------> SO₃ (g)    ΔG⁰ = -371 kJ -------> equation (1)

2SO₂(g) + O₂(g) ------------> 2SO₃ (g)    ΔG⁰ = -142 kJ -------> equation (2)

Our target equation is S(s) + O₂(g) ------------> SO₂ (g)

Step 3:

Now our target equation has no SO₃, so we reverse equation 2 and multiply  by 1/2 to cancel the SO₃

1/2 × [ 2SO₃ (g)   ------------> 2SO₂(g) + O₂(g)   ΔG⁰ = -142 kJ ]

SO₃ (g)   ------------> SO₂(g) + 1/2O₂(g)   ΔG⁰ = +71 kJ -----> equation(3) [note: sign will reversed so it becomes +ve and value is also multiply by 1/2 so it becomes half of original value ]

Step 4:

Now add equation (1) and (3) and equation to get the target equation

S(s) + 3/2 O₂(g) ------------> SO₃ (g)    ΔG⁰ = -371 kJ

SO₃ (g)   ------------> SO₂(g) + 1/2O₂(g)   ΔG⁰ = +71 kJ

On adding the all the above equation we get

S(s) + 3/2 O₂(g) +  SO₃ (g) -----------> SO₃ (g) + SO₂(g) + 1/2O₂(g) ΔG⁰ = -371 kJ + ( 71 kJ ) = -300 kJ

Now, similar like species will cancel out ( here SO₃ (g) , 1/2 O₂(g) will cancel out ) from each side of reaction

So overall equation will becomes  

S(s) + O₂(g) ----------->  SO₂(g)   ΔG⁰ = -300 kJ

(1) Hence   ΔG⁰ of the reaction is   -300 kJ

(2) yes the reaction is spontaneous

[ because if a reaction is exothermic the free energy change ( ΔG⁰ ) is negative and the reaction is always spontaneous.]