Endothermic reactions, continued: thermal equilibrium

Since someone asked:

In the case of the endothermic reaction that you posted a video for – how was it that it turned so cold? I still don’t quite get how it’s freezing, even though it’s absorbing heat. Or is that everything that I see turning cold is part of the surroundings and not the system undergoing the heat-absorbing reaction?

In the video of the endothermic reaction, it’s important to note that heat transfer is taking place between the reaction and its surroundings!  Given long enough, the super-cold flask and the room-temperature board it sits on will reach thermal equilibrium and will be at the same temperature.  You could even calculate that temperature using the handy equation we learned last time in class: q = m • c • ∆T.  The reaction flask is definitely absorbing heat, it’s just that the board isn’t warm enough to bring it to room temperature!

If we were to carry out the reaction in an insulated thermos, do you think it would still freeze the water on the board?

PS: many of you seem to think that the homework is due this Wednesday.  You may want to check the schedule…but I am certainly not going to stop anyone from working ahead!


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