1. Solid --> Liquid --> Gas is an Endothermic Process (Delta H is positive)
2. Solid <-- Liquid <-- Gas is an Exothermic Process (Delta H is negative)
Before we make sense of this. Consider Heat = Energy
In the first process where you go from solid to gas (Ice to water vapor). You are adding heat/energy. Where is this heat coming from? The surroundings/flame/a stove. So in endothermic processes, the surrounding looses heat (gets cooler)
As for the second process, you are removing heat. In order to turn water into ice (i.e. liquid into a solid) one must remove heat/energy from it. So then where is this energy going? Must be going to the surroundings. If it's going to the surrounding then it must be Releasing energy.
We can further simplify this discussion by considering where the heat or energy is going or coming from. If the surrounding is getting warmer/gaining energy then we know its exothermic and if the surrounding is getting cooler/losing energy then we know its endothermic.
Hope it helps.
