Week 3&4 Achieve #3

[Ashley_Kim_3H]

The question asks: Classify the processes as endothermic or exothermic.
The given examples are: water condensing on a surface, baking a cake, ice melting, the chemical reaction inside an instant cold pack, a car using gasoline

What's an easy way to process questions like these where examples are given and I classify whether they are endothermic or exothermic?

[Alba Mendis 1A]

Exothermic reactions give off heat/energy, so if something cools down, it's definitely exothermic! Also try to remember that forming bonds releases energy (atoms are stabilized and thus are at a lower energy level, if that makes sense), which explains why condensation is exothermic in the problem. Endothermic reactions are the opposite. If the system is gaining heat or bonds are breaking up, then it's endothermic. Hopefully this helped!

[Varchas Bharadwaj 2G]

The way I would approach these problems is to identify the system and determine whether it cools down or heats up. If it cools down, it's an exothermic reaction (since the system losing heat), and if it heats up, it's an endothermic reaction (since the system is gaining heat). For the case of your examples, the water is cooling as it condenses, so the reaction is exothermic; the cake is heating up as it bakes, so the reaction is endothermic; the ice is heating up as it melts, so the reaction is endothermic; and so on.

[Sunny Do 1G]

Endothermic reactions require heat to proceed and exothermic reactions release heat. For example, if you want to melt ice, you would need heat and energy to go from solid to liquid. Melting is an endothermic level. You can also view that on a molecular level. When there is more energy, molecules will move faster in liquid compared to solids, which have less energy.

[Gavin_Yang_1J]

For reactions that aren't necessarily simple state changes like the reaction inside a cold pack you can think about what the purpose of the reaction is. Even if we don't know how the reaction works we know that the point of the cold pack is to become colder after the reaction than before, which means it would have to be endothermic.