JEE Main · 2005 · 08 May 2005 · Offline · Chemical Thermodynamics

The van't Hoff equation written as $\ln K_{eq}=-\frac{\Delta H}{R}\cdot \frac{1}{T}+\frac{\Delta S}{R}$ turns a plot of $\ln K_{eq}$ against $1/T$ into a straight line of slope $-\frac{\Delta H}{R}$. The sketch rises as $1/T$ increases, a positive slope, which forces $-\frac{\Delta H}{R}>0$ and hence $\Delta H<0$. A negative reaction enthalpy is the signature of an exothermic reaction.