Temperature and Exothermic Reaction [ENDORSED]

[Michelle Dong 1F]

In lecture, Dr. Lavelle talked about how the temperature doesn't necessarily change in an exothermic reaction, even though an exothermic reaction suggests a net release of heat. Can someone explain this?

[K Stefanescu 2I]

If the vessel/beaker holding the reaction is placed in a temperature-controlled tub, then as the exothermic reaction is giving off heat, the sensor controlling the temperature of the tub will make it so the tub itself always remains at the same temperature. It will adjust to make up for the extra heat coming from the reaction vessel, thus cooling the tub to result in a net temperature change of zero.

[Tim Nguyen 2J]

I think he was specifically referencing the example/problem he gave in class with the fishbowl and test tube where an exothermic reaction occurred at a constant temperature with that device in the fishbowl. There was a system where an exothermic reaction occurred inside the test tube (which is slightly submerged in the water kept at a constant temperature of say 25 degrees Celsius by an external device). Within that test tube, yes, the exothermic reaction released heat due to its exothermic nature. But a minor confusion was understanding how temperature remained constant if heat was released into its surroundings.

The 25 degrees Celsius water is the surrounding environment and temperature the reaction is subjected to inside the test tube. It is being kept constant at this temperature because of the external device (from what I understood in lecture). The heat would be released into the surrounding water, but the external device would take the heat energy into account and use enough energy to cool it back down to 25 degrees Celsius at all times. Therefore, the exothermic reaction would be occurring in a constant temperature environment with the help of the device.

tl;dr: the surrounding temperature in which an exothermic reaction occurs can be kept constant by an external device compensating for the release of heat (i.e. the one used in the fishbowl example if what I heard in lecture was correct)

[Salman Azfar 1K]

A quick and easy way to put it is that the temperature is technically changing but tech is being used to keep it constant anyway.

[Chem_Mod]

A key aspect of thermodynamic analysis: surroundings are bigger than the system.

An example:

It is cold today. Go outside and light a match (system/reaction).
The burning match is exothermic.
Did the temperature outside (surroundings) change?

:-)

Remind me in class next week when we discuss systems and surroundings as part of thermodynamics.
This week we are doing thermochemistry.