Exercise 1 solution

Rule: exothermic = energy released to the surroundings (they warm up). Endothermic = heat absorbed from the surroundings (they tend to cool).

(a) Flask warms from 20 C to 35 C: EXOTHERMIC. The surroundings gain heat (a rise of 15 C).
(b) Water evaporating: ENDOTHERMIC (evaporation is on the Endothermic process article's list). The surroundings lose heat.
(c) Ammonium nitrate dissolving and getting colder: ENDOTHERMIC (also on that article's list). The surroundings lose heat, so it feels cold.
(d) Wood burning: EXOTHERMIC (burning fuels, Exothermic process article). The surroundings gain heat and light.
(e) Rain forming from water vapour: EXOTHERMIC (condensing rain is on the Exothermic process article's list). The surroundings gain heat.

Tip: judge by what happens to the SURROUNDINGS' temperature, not the substance's.
Note: arithmetic 35 - 20 = 15 C (my own working) (check).