chemistry

http://pmt.physicsandmathstutor.com/download/Chemistry/A-level/Topic-Qs/OCR-A/5-Physical-Chemistry-Transition-Elements/Set-B/Enthalpy%20and%20Entropy.pdf

question 6b,

it says use data from part aii
I don't understand which ones from part aii we have to use and why??

YOu need to work out the enthalpy change for this reaction and then substitute into Gibbs free energy equation.

To work out the enthalpy change you have to break the equation down into a series of energetic steps:

BaCl₂ --> Ba²⁺(g) + 2Cl^-(g) ..............is the first step (the endothermic lattice enthalpy)

... can you take it from here?

No not sure
How do we calculate the enthalpy change?

The sum of the individual steps.

Your target equation is

BaCl₂(s) --> Ba(s) + Cl₂(g)

I showed you the first step:

BaCl₂ --> Ba²⁺(g) + 2Cl^-(g)

Now the next step is:

Ba²⁺(g) + 2Cl^-(g) --> Ba(g) + 2Cl(g) (actually two steps combined)

Then

Ba(g) + 2Cl(g) --> Ba(s) + Cl₂(g) (once again two steps combined)

You add up the energy changes for each of these steps by consulting the data table

How are we supposed to know that we have to use these individual steps and combine? Can't remember learning content on this (combing steps).

It is precisely what you do when you use a Born-Haber cycle!

I'm stuck on this question.
Why is it ΔH = 859 × 1000

Maybe you should check out the Born-Haber cycle for barium chloride

Can you show me the numbers we are adding up?
Also isn't Enthalpy of formation of barium chloride, the enthalpy change we need to calculate temperature?