Two examples of chemical reactions that involved a thermal energy change: 1. NH4NO3 (s) + heat ---> NH4+ (aq) + NO3 (aq)
2. CaCl2 (s) + 2H20 ---> Ca(OH)2 (aq) + 2HCl (g) + heat
Which is exothermic? Which is endothermic? How do you know?

Option 1 is endothermic

Option 2 is exothermic

Explanation:

In Chemistry, Exothermic reactions are reactions whereby heat energy is transferred to the surroundings and the temperature of the surroundings increases. Endothermic reactions are those whereby heat energy from the surroundings is absorbed and thereby making the temperature of the surroundings to decrease.

This means in simple terms that endothermic reactions will have heat on the reaction side of the equation while exothermic will have heat on the product side of the equation.

Thus;

Option 1 is endothermic since it has heat absorbed on the reactant side.

Option 2 is exothermic since it gives off heat on the product side.

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