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. (c)
Solution:
- From thermodynamics,
$$ \ln k=\frac{-\Delta H^{\circ}}{R T}+\frac{\Delta S^{\circ}}{R} $$
Mathematically, the equation of straight line is
$$ y=c+m x $$
After comparing Eq. (ii) with (i) we get, slope $=\frac{-\Delta H^{\circ}}{R}$ and intercept $=\frac{\Delta S^{\circ}}{R}$
Now, we know for exothermic reaction $\Delta H$ is negative (-)ve. But here,
$$ \text { Slope }=\frac{-\Delta H^{\circ}}{R} \text { is positive } $$
So, lines $A$ and $B$ in the graph represent temperature dependence of equilibrium constant $K$ for an exothermic reaction as shown below
