Change in Temperature

[Aren_Kasparian_1G]

How is there no net change in temperature in endothermic or exothermic reactions, when heat is added or removed from the reaction?

[Michael Crannell 1H]

I am not entirely sure but I know the professor put an emphasis in lecture today that we examine reactions at a consistent temperature to help ensure correctness and make things easier. For example a exothermic reaction could occur but the final temperature will return back to the initial state so it appears no temp change occurred.

[Rachel Chan 1B]

I understand that temperature may not change in two scenarios.

1) If a phase transition/change is occurring, the temperature (aka heat released into the environment) is not changing because the heat is instead being used to break the chemical bonds (like breaking hydrogen bonds to change from a solid to a liquid). If the phases are not changing, then the heat will directly translate to heat released into the environment since the system is not actively using the heat for breaking bonds. Think about the heating curve of water he showed in lecture where there was a flat line when the phases were changing.
2) Initially a reaction (contained within a system) may occur to completion, releasing or absorbing a lot of heat in the process. However, the reaction now needs to shift to be at equilibrium with the system, since the place where the reaction happened may be super warm (released heat) but the system surrounding it is super cold (because it absorbed this new heat). After some time, heat will transfer from the system to the reaction since the heat amounts in both places need to be equal. Therefore, heat can be transferring in both directions even as temperature doesn't change. (I'm a bit uncertain on this second scenario though)

[Rachel Fox - 3F]

As mentioned in the other responses, temperature might not change in exothermic/endothermic reactions if a phase change is occurring, as it takes energy to break the bonds to cause the phase change. This means that the energy is not used to increase molecular movement (increase temperature) but instead is used to break bonds. Also in lecture, Dr. Lavelle mentioned that an exothermic reaction could have the system temperature not change if the test tube is in a heat bath where temperature of the surroundings is controlled, so the heat would not be transferred to increasing the temperature of the surroundings. The temperature may not change in equilibrium reactions between the initial temperature and the equilibrium temperature, and the amount of energy released can be measured under this constant temperature.