Exothermic and Endothermic - HQ

Question 1

Exothermic reaction

Answer 1

Involves an energy transfer from the system to the surroundings, resulting in a temperature increase.

Question 2

Endothermic reaction

Answer 2

Involves an energy transfer (absorption) from the surroundings to the system, resulting in a temperature decrease.

Question 3

Why do exothermic/endothermic reactions happen?

Answer 3

All substances have stored chemical potential energy, due to the attractive and repulsive forces between the particles
making up the substances.
* The particles of different substances are held together by bonds of varying strengths, hence every substance will probably possess a unique amount of potential energy
* It therefore follows that in a chemical reaction, the products formed will most likely have different potential energies to the reactants

Question 4

Why do exothermic reactions release energy?

Answer 4

The products are more “stable” than the reactants, thus excess potential energy is released to the surroundings

Question 5

Why do endothermic reactions absorb energy?

Answer 5

The products are less “stable” than the reactants, thus deficient potential energy is absorbed by the system

Question 6

Why are some reactions endothermic and some exothermic?

Answer 6

• Almost all reactions require bonds breaking and bonds forming
• Bond breaking requires energy and is endothermic
• Bond forming releases energy and is exothermic
• If the amount of energy required to break the bonds is less than the amount of energy released in the formation of bonds, the reaction is exothermic, and vice-versa