Hess's Law

Question 1

What does Hess’s law state?

Answer 1

The overall enthalpy change for a reaction is the same whatever route is taken

Question 2

What are the 3 steps for calculating enthalpy change using an enthalpy cycle?

Answer 2

Step 1: write the equation for the enthalpy change you want to know
Step 2: fill in an alternative route, using enthalpy change values you do know
Step 3: start at the start and go and go round the alternative route to the end (if you go with the arrow, keep the sign & vice versa)

Question 3

Which direction do the arrows in an enthalpy cycle go when enthalpy change of combustion is given?

Answer 3

Down

Question 4

Which direction do the arrows go in an enthalpy cycle when enthalpy change of formation is given?

Answer 4

Upwards