U3-3-1 - Energy Changes

Question 1

Enthalpy

Answer 1

A measure of the chemical energy in a substance.

(symbol is H)

Question 2

What is ∆H?

Answer 2

Enthalpy change - energy difference between reactants and products.

Question 3

If a reaction is exothermic, ∆H is…

Answer 3

negative.

(∆H < 0)

Question 4

If a reaction is endothermic, ∆H is…

Answer 4

positive.

(∆H > 0)

Question 5

What is X?

Answer 5

Enthalpy change

Question 6

Why is it important to know if a reaction is exothermic or endothermic?

Answer 6

Any one of:

• If reactions are exothermic, heat will need to be removed
• If reactions are endothermic, heat will need to be supplied
• So that chemists can create conditions to maximise yield