JEE Main201815 Apr 2018Evening ShiftChemistryThermodynamics (C)Actual
Given (i) 2 Fe ₂ O ₃( ~s ) 4 Fe ( s )+3 O ₂( ~g ) ; _ r G ^ =+1487.0 ~kJ ~mol ⁻¹ (ii) 2 CO ( g )+ O ₂( ~g ) 2 CO ₂( ~g ) ; _ r G ^ =-514.4 ~kJ ~mol ⁻¹ Free energy change, _ r G ^ for the reaction 2 Fe ₂ O ₃( ~s )+6 CO ( g ) 4 Fe ( s )+6 CO ₂( ~g ) will be:
Options
- A-112.4 ~kJ ~mol ⁻¹
- B-56.2 ~kJ ~mol ⁻¹
- C-208.0 ~kJ ~mol ⁻¹
- D-168.2 ~kJ ~mol ⁻¹
Correct answer
B. -56.2 ~kJ ~mol ⁻¹
Step-by-step solution
(i) 2 Fe ₂ O ₃( ~s ) 4 Fe ( s )+3 O ₂( ~g ) ; _ r G ^ =+1487.0 ~kJ ~mol ⁻¹ (ii) 2 CO ( g )+ O ₂( ~g ) 2 CO ₂ (g) _ r G ^ =-514.4 ~kJ ~mol ⁻¹ Multiple reaction (ii) with 3 , we get (iii) 6 CO ( g )+3 O ₂( ~g ) 6 CO ₂( ~g ) ; _ r G ^ =3 -514.4=-1543.2 kJmol ⁻¹ When we add reaction (i) and reaction (iii), we get reaction (iv) (iv) 2 Fe ₂ O ₃( ~s )+6 CO ( g ) 4 Fe ( s )+6 CO ₂( ~g ) Free energy change, _r G^ for the reaction will be 1487.0-1543.2=-56.2 ~kJ ~mol ⁻¹