Thermodynamics

Thermodynamics

Question

The standard Gibbs energy change at 300 K for the reaction, 2A  ⇌ B +C is 2494.2J at a given time, the composition of the reaction mixture isleft square bracket straight A right square bracket space equals space 1 half comma space left square bracket straight B right square bracket space equals 2 and left square bracket straight C right square bracket space equals space 1 half, The reaction proceeds in the [R= 8.314 JK/mol, e = 2.718]

  • forward direction because Q>Kc

  • reverse direction because Q>Kc

  • forward direction because Q < Kc

  • reverse direction because Q < Kc

Answer

B.

reverse direction because Q>Kc

We know,
ΔG = ΔGo + RTlnQ .. (i) 
Given,
ΔGo  = 2494.2J
 straight Q space equals fraction numerator left square bracket straight B right square bracket right square bracket straight C right square bracket over denominator left square bracket straight A right square bracket squared end fraction space equals space fraction numerator 2 space straight x begin display style 1 half end style over denominator open parentheses begin display style 1 half end style close parentheses squared end fraction space equals space 4
thus,
putting the value in equation (i)
 = 2494.2 +8.314 + 300 In 4
= 28747.27 J
= positive value
Also, we have
increment straight G space equals space RT space ln space straight Q over straight K
If ΔG is positive, Q >K
therefore, reaction shifts in the reverse direction

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