A reaction mixture in a beaker becomes noticeably cold. This shows that the reaction is

A. exothermic, since heat leaves the system
B. at equilibrium
C. endothermic, since heat is absorbed from the surroundings
D. catalysed

Explanation

The system draws energy from its surroundings, and since the beaker and the solution are those surroundings their temperature falls. Dissolving ammonium chloride or ammonium nitrate in water is the usual classroom demonstration, and it is the principle behind an instant cold pack. An exothermic reaction would make the beaker warm instead.

A reaction mixture in a beaker becomes noticeably cold. This shows that the reaction is

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