I am struggling with question 3aiii from the 2020 paper (Chemical Reactivity).
Here’s a screenshot:
My response was:
The lower value of Kc shows that there are fewer products and more reactants present. This means the reverse reaction has taken place.
I didn’t understand the answer in the marking schedule. What is ‘K?’ And how do we calculate it?
If there are any other gaps you see in my understanding, please feel free to point them out. Always eager to learn more
Thanks for that. It makes sense
In Q3iii, the marking scheme referred to ‘K.’ Is this the same thing as ‘Kc?’ Or is it something different?
K is a generic term which represents any equilibrium constant, while Kc is the value of the equilibrium constant in terms of concentration of products and reactants - in this context I think they are pretty much the same thing though
Good response Emilie. But I would note a couple of things.
One is that the idea that K=1 is the cutoff for whether products or reactants are favoured is only a rough guideline as the maths changes when exponents need to be taken into account. So a more realistic guidline is that values of K> 100 will probably favour products and values of K< 0.01 will probably favour the reactants
Because if this the answer provided to the exam question is not as good as it can be. Instead it should have stated that because at the new tenperature the value of K has DECREASED from 200 to 50, this means the equilibrium position has shifted to favour the reactants.