# Confusion in understanding temperature change in exothermic reactions

The question due to which my doubt arose $\ce{->}$

The following system is in equilibrium: $\ce{SO2Cl2 + {Heat} -> SO2 +Cl2}$

What will happen to the temperature of the system initially if some $\ce{Cl2}$ is added into it at constant volume ?

My attempt at the question : Since if we add more $\ce{Cl2}$, concentration of products will increase which will in turn shift the equilibrium in backward direction, which will in turn release more heat. And since the heat is being released to the surrounding, temperature of the system should decrease.

Though according to my textbook the answer is temperature of the system will increase.

So please do explain where my understanding is wrong.

• Is the reaction exothermic or endothermic, that is, what is the sign of $\Delta T$?
– Zhe
Mar 25, 2017 at 21:03
• @zhe reaction is endothermic as heat is being supplied Mar 25, 2017 at 21:49
• The system is in thermal equilibrium with the surroundings. If the temperature of the surroundings increase, then the temperature of the system will increase...
– Zhe
Mar 25, 2017 at 22:04
• @zhe Can you please explain your reply in detail . If the system is in thermal equilibrium then the temperature of both system and surrounding would always be same ? Mar 25, 2017 at 22:10
• And how do we know that the system is in thermal equilibrium ? Are all chemical reactions in equilibrium are also assumed to be in thermal equilibrium . Mar 25, 2017 at 22:12