Constant Temperature

[Michelle Zhang 1J]

In lecture today, Dr. Lavelle explained how an endothermic reaction in a beaker that is in a cold water bath can have constant temperature. I am still not quite sure how that happens. I understand that the water absorbs the most of the heat released by the reaction, but doesn't the temperature of the water and the beaker both increase at least a little? If the water is too cold, doesn't the beaker temperature also decrease then?

[Anna Dai-Liu 3B]

I think he explained that even though there is some heat released over the progress of the reaction, measurements are only taken when the reaction has reached equilibrium, giving time for that heat to dissipate in the large body of water and for the reaction tube to return to its original temperature.

[Sara Shimabukuro 1A]

Yes, even though the temperature changes at first, the temperature and the beaker are not measured again until they have returned to the original temperature.

[Arjan G 2H]

Hi! Like Dr. Lavelle explained in the lecture, enthalpy measures the change in heat of a reaction, and it is not a state property, meaning we need to know the exact details of its pathway to calculate it. But, the temperature is a state property, meaning the initial and final values are the only ones that matter, and they both must be the same before you measure enthalpy. While it seems like heat can have an effect on temperature, these are two separate things when looking at a chemical reaction. The heat that is being absorbed or released in a reaction is intended to either create or break bonds within the substances of the reaction, rather than change the overall temperature. Typically, the heat is used during the phase transitions of a reaction, and the temperature is only measured initially and after the reaction occurs. But, the temperature must remain constant, so the enthalpy, or change in heat, of a reaction is measured once the reaction goes back to the initial temperature it began at. I hope this helps!

[Harsimer Bal 3K]

Hi! As others mentioned, temperature does change when heat is added to a beaker of cold water in an endothermic reaction but the difference in temperature is 0 when enthalpy is measured because the reaction must go back to equilibrium before it is measured as temperature is a state value. Thus, it can be said that the heat supplied goes towards breaking bonds and not changing the temperature.

[Grace Chen 3F]

I think temperature does change during the process of the reaction. However, it will ultimately return to the initial temperature at equilibrium. So, the NET change of temperature is 0, but temperature did change when the reaction progresses.

[Abby Citro 2A]

Even though the temperature does change during the reaction, the temperature will ultimately return to equilibrium, resulting in a net temperature change of 0.

[Minoo Bastani 2J]

I think what he was getting at was that there is no net change in temperature even if a reaction is exothermic because when you measure the temperature of the system both before the reaction occurs and when the reaction is complete (@ equilibrium), the system will be at the same temperature.