Enthalpy Changes

Question 1

what is the enthalpy change of a reaction?

Answer 1

the heat energy it releases or absorbs per mole

Question 2

what is the symbol for enthalpy change?

Answer 2

ΔH

Question 3

what sign is used for endothermic reactions and what does it tell us about the heat energy?

Answer 3

positive (+) and the heat energy has been absorbed

Question 4

what sign is used for exothermic reactions and what does it tell us about heat energy?

Answer 4

negative (-) and the heat energy has been released

Question 5

what does enthalpy change tell us?

Answer 5

• the value tells us how much heat energy is absorbed or released
• the units are always kJ/mol so that different reactions can be compared easily

Question 6

what does heat energy absorption or release depend on?

Answer 6

the balance between:

• breaking bonds, which absorbs energy
• making bonds, which releases energy