DF2 - Enthalpy Cycles and Hess's Law

Question 1

NOTE:

The key idea of enthalpy cycles is that

the total enthalpy change for the INDIRECT route is the SAME as the enthalpy change via the DIRECT route.

Energy cannot be created or destroyed – law of conservation of energy.

So as long as the start and finishing points are the same, the enthalpy change will always be the same, irrespective of how you get from start to finish.

Answer 1

NOTE:

The key idea of enthalpy cycles is that

the total enthalpy change for the INDIRECT route is the SAME as the enthalpy change via the DIRECT route.

Energy cannot be created or destroyed – law of conservation of energy.

So as long as the start and finishing points are the same, the enthalpy change will always be the same, irrespective of how you get from start to finish.

Question 2

When both arrows in a Hess’s cycle point down, how do you work out ΔH1?

Answer 2

ΔH1 = ΔH2 - ΔH3

Question 3

When both arrows in a Hess’s cycle point up, how do you work out ΔH1?

Answer 3

ΔH1 = - ΔH2 + ΔH3

Question 4

Define specific heat capacity.

Answer 4

The amount of energy needed to raise the temperature of 1g of a substance by 1 K.