Chemical Energetics (ch5)

Question 1

What happens during a physical and a chemical change?

Answer 1

During a physical or a chemical change, there is exchange of heat energy with the surroundings

Question 2

What does exothermic mean?

Answer 2

It means that the reaction released more energy than absorbing it. It means more bonds are formed and that DH = negative. It also increases the temperature of the surrounding.

Question 3

What does endothermic mean?

Answer 3

It means that the reaction absorbed more energy than releasing it. It means more bonds are broken and that DH = positive. It also decreases the temperature of the surrounding.

Question 4

What are the physical changes in the state of matter?

Answer 4

Gas—Solid = EXO (solidification)
Solid—Gas = ENDO (sublimation)
Gas—Liquid = EXO (condensation)
Liquid—Gas = ENDO (boiling/evaporation)
Liquid—Solid = EXO (freezing)
Solid—Liquid = ENDO (melting)

Question 5

What is Enthalpy change/Energy change?

Answer 5

The difference in energy content of the reactants and the products involved in a chemical reaction

Question 6

Explain in terms of bond breaking and bond making why the overall reaction is endothermic/exothermic?

Answer 6

Bond breaking is endothermic. Bond making is exothermic.

More heat energy is released so reaction is exothermic.

More heat energy is absorbed so reaction is endothermic.

Question 7

What is activation energy?

Answer 7

The minimum amount of energy absorbed by the reactants to start a chemical reaction. It is positive (for both ENDO and EXO)