For example. There are three chemicals. Chemical A,B,C

  • Chemical B react with Chemical A = heat
  • Chemical B react with Chemical C = cold

Is there any chemical available like this? And is it safe to use? Easy to create OR available at home/market?


1 Answer 1


Yes there is, chemical B is water.

If we take ammonium nitrate as chemical A and then react it with chemical B by dissolving it then the temperature of the mixture will go down. The chemical reaction which transforms either crystalline ammonium nitrate or choline chloride into an aqueous solution of the ions is an endothermic reaction.

One of my academic interests revolves around strong aqueous solutions of sodium chloride and also strong solutions of choline chloride. I have found when I have been making solutions such as 6 M choline chloride in water that when I add the water the mixture cools far below room temperature.

What is happening is that the reaction is being driven forwards by the fact that the randomness (entropy, $S$) of the system greatly increases. This overcomes the energy (enthalpy, $H$) demand of the reaction.

$$\Delta G=\Delta H-T\,\Delta S$$

When $\Delta G$ is the change in Gibbs free energy for the reaction, when $\Delta G$ is negative then the reaction is thermodynamically able to go ahead without anything outside the system driving it forwards. The $\Delta H$ and $\Delta S$ terms are the changes in the enthalpy (energy) and entropy (randomness) of the system.

For an exothermic reaction between water and something else we have quite a lot of choices, both sodium hydroxide and concentrated sulfuric acid when mixed with water undergo exothermic reactions which release lots of heat.

So I would say that C should be concentrated sulfuric acid.

When I was young my grandfather told me a horror story about a man who attempted to dilute concentrated sulfuric acid in the hand basin in a toilet. The exothermic reaction caused the basin to crack and fall off the wall onto the floor. I would chalk this one up as something not to try either at home or in the "Gents". I also consider it something which female chemists should not attempt in the "Ladies".

  • $\begingroup$ I appreciate your response and in-depth knowledge in Chemistry. Thanks for the answer. I just want you to know that I want to create a pouch (those heat/cold shake pouches) but you can choose that you want heat OR cold pouch inside single pouch. No need two different pouches for different temperature. Well, I understand the risk behind dangerous chemicals and specially H2SO4 (experience lol) so I will check and research more about this. Thanks again $\endgroup$
    – Weirdo
    Feb 11, 2023 at 9:37

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