If ammonium nitrate and calcium hydroxide are added at the same time, a chemical reaction will occur. The products of this reaction will be calcium nitrate, water, and ammonia. The reaction can be represented by the following equation:

$$2NH_4NO_3 + Ca(OH)_2 → Ca(NO_3)_2 + 2H_2O + 2NH_3$$

The reaction is exothermic, meaning that it releases heat. The heat released by the reaction can cause the mixture to boil and splatter. The ammonia gas produced by the reaction is also toxic and can cause respiratory problems.

For these reasons, it is important to be careful when mixing ammonium nitrate and calcium hydroxide. It is best to add the two chemicals slowly and carefully, and to avoid contact with the mixture.