Why is PCL3 and Cl2 produced in equal amounts?

See attachment

Look at the balanced equation:

PCl₅ ==> PCl₃ + Cl₂
for every PCl₃ formed there must also be one Cl₂ formed


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So in terms of moles they are the same in terms of products and reactants so should PCl5 be the same as the others?

No, because PCl₅ has to break down to give the others.

If x mol of PCl5 breakdown then x mol of the other two will be formed, but the mol of PCl₅ must be (original mol - x)

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No, because PCl₅ has to break down to give the others.

If x mol of PCl5 breakdown then x mol of the other two will be formed, but the mol of PCl₅ must be (original mol - x)

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So do you mean AB --> A + B?
So the partial pressures must sum to give AB?

I never mentioned partial pressures ...

In terms of moles.

If the initial mol of PCl₅ is n
and the mol of PCl₅ decomposed is x

Then the final mol of each component:

PCl₅ = (n-x)
PCl₃ = x
Cl₂ = x

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Perfect. I get it now

I never mentioned partial pressures ...

In terms of moles.

If the initial mol of PCl₅ is n
and the mol of PCl₅ decomposed is x

Then the final mol of each component:

PCl₅ = (n-x)
PCl₃ = x
Cl₂ = x

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So if CaCO3--> CaO + O2


So does this only work for homogeneous systems?
Can I use it for the decomposition of Calcium Carbonate?

You cannot have the concentration of a solid, or a pure liquid.


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I think get it so for (aq) or (g) equations.

The moles relationship works of course, but you cannot do equilibrium calculations without (aq) or (g)


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So all species have to have the same state of matter?

This is from the CGP textbook page 315. I'm confused about the state of matter stuff now.

Notice they say kp.

This is the equilibrium constant with regard to partial pressures. It can only apply to gases.

Kc applies to solutions or gases.


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