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The above diagram gives the potential energy profile of the catalyst and uncatalysed reactions of...

Chemistry
JAMB 1989

The above diagram gives the potential energy profile of the catalyst and uncatalysed reactions of X(g) + Y(g) → XY(g). Deduce the respective activation energies in KJ of the catalysed and uncatalysed reverse reactions: XY(g) → X(g) + Y(g)

  • A. 300, 500
  • B. 500, 300
  • C. -300, -500
  • D. -500, -300
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Correct Answer: Option A
Explanation

Activation energy, E\(_a\) of catalysed reaction is 400 - 100kJ = 300kJ and the activation energy, E\(_a\) of uncatalysed reaction =  600 - 100kJ = 500kJ 

or

The catalysed reaction = 100 - 400 = -300 

The uncatalysed reverse reaction = 100 - 600 = - 500. From the profile diagram, the forward reaction is an exothermic, ΔH = - ve, - (- 300) = 300kJ
Also, since the forward reaction was exothermic, the reverse reaction will be endothermic, which means ΔH = + ve . Therefore, uncatalysed reversible reaction will be 500kJ.

Consequently, the correct answer is Option A - 300, 500kJ 


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