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Usually when one thinks of endo- and exothermic reactions in chemistry, one thinks of acid-base neutralizations, or oxidation-reductions. But let's look even more fundamentally - at the simple making of solutions. One of the following "reactions" is endothermic and the other is exothermic. See if you can explain why they are that way.
The first thing we must have at hand are our three components - all equilibrated at room temperature: water, 100% ethanol, and solid NaCl.
Our first experiment is of the non-ionic type in which equal volumes of water and ethanol are dumped together, rapidly swirled and any temperature change is noted.
The second experiment will see us dissolve 25 grams of NaCl in 100 ml of water. Again the resulting change in temperature will be noted.
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