CHEMISTRY COMMUNITY

Can someone please explain the difference between endothermic and exothermic?

Exothermic reactions favor the formation of products and give off heat. Endothermic reactions favor the formation of reactants and require heat.

An exothermic reaction has a negative delta H while an endothermic reaction has a positive delta H. Delta H=Change in enthalpy.

The two posts before are really standard definitions. In other words, you can simply regard the exothermic reaction as a "releasing heat" process. On the other hand, you can regard endothermic reaction as an "absorbing heat" process.

Exothermic is a reaction that releases heat. Its delta H is negative, < 0. Endothermic is a reaction that absorbs heat from its environment. Its delta H is positive, > 0.

Endothermic has a positive delta G and exothermic has a negative delta g. Endothermic requires heat and exothermic releases heat. Endothermic favors product formation and exothermic favors reactant formation.

Endothermic: When energy is absorbed from its surroundings. delta H>0
Exothermic: When energy is released. delta H<0

If the reaction gives a release of heat (-delta H), the reaction is exothermic. If the reaction requires heat (+delta H), the reaction is endothermic.

Professor Lavelle gave example of a hot/cold pack during lecture one day, and I thought it was helpful.

Endothermic reactions require heat to obtain the products (delta H = positive) while exothermic reactions release heat during reactions (delta H = negative). Given that, with a hot pack, when you break the bag in inside, it becomes warm. That’s because the bag inside the hot pack undergoes an exothermic reaction, meaning it’s giving off heat which causes the bag to warm up. For the cold pack, upon breaking the bag inside the pack, an endothermic reaction takes place. The reaction absorbs heat from the surrounding and uses to form its products, which is why the pack turns cold.

Hope this helps!

Exothermic reactions release energy, delta H is negative, and heat is a product. Endothermic reactions absorb energy, delta H is positive, and heat is a reactant.