Chemical Kinetics - Result Question 14
17. Which of the following lines correctly show the temperature dependence of equilibrium constant, $K$, for an exothermic reaction?
(2018 Main)
(a) $A$ and $B$
(b) $B$ and $C$
(c) $C$ and $D$
(d) $A$ and $D$
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Answer:
Correct Answer: 17. (a)
Solution:
- From thermodynamics,
$ \ln k=\dfrac{-\Delta H^{\circ}}{R T}+\dfrac{\Delta S^{\circ}}{R} $$\quad$ …….. (i)
Mathematically, the equation of straight line is
$ y=c+m x $$\quad$ …….. (ii)
After comparing Eq. (ii) with (i) we get,
slope $=\dfrac{-\Delta H^{\circ}}{R}$ and intercept $=\dfrac{\Delta S^{\circ}}{R}$
Now, we know for exothermic reaction $\Delta H$ is negative (-)ve. But here,
$ \text { Slope }=\dfrac{-\Delta H^{\circ}}{R} \text { is positive } $
So, lines $A$ and $B$ in the graph represent temperature dependence of equilibrium constant $K$ for an exothermic reaction as shown below
BETA
