You will be familiar with the idea of reversible reactions from GCSE, and hopefully also you have used le Chatelier’s principle to predict how changing the conditions of a reversible reactions affects amounts of reactants and products.
At A level we need to be 100% confident in our understanding of these foundational ideas before we tackle the maths side of things, hence I start with exploring the concept of position of equilibrium which is often very poorly understood by students.
There are lots of practice questions and fully explained answers for each section, including some fiendishly difficult ones to stretch and challenge 😊.
What is the position of equilibrium for a reversible reaction?
‘Position of equilibrium’ is a phrase we were throwing around back in GCSE when we talking about reversible reactions, but what does it actually mean?
What is le Chatelier’s Principle?
We use le Chatelier’s principle to explain how changing the conditions of a system at equilibrium affects the position of equilibrium but more importantly, we can use it to manipulate reversible reactions to favour a particular product which is exceedingly useful.
How to find the equilibrium constant for a reaction
Kc is basically a ratio – the concentrations of the products at equilibrium divided by the concentration of the reactants – and it tells us exactly where the position of equilibrium lies.
Why don’t reactions at equilibrium go to completion?
In order to answer the question we need to look at the position of equilibrium through the lens of Gibbs energy …
Calculating Kp, the equilibrium constant, for a gaseous system
• Calculating the partial pressure of a gas
• How to write an expression for Kp
• lots and lots of Kp exam style calculations
Understanding the relationship between Kc and Kp
We can derive a value for the equilibrium constant in a gaseous equilibrium system either using partial pressures, Kp, or concentrations ,Kc, which means the two must be related.
What is the solubility product?
Many ionic salts are only very sparingly soluble – find out how to calculate their solubility and a value for Ksp, the solubility product.
What is the common ion effect?
If I try to dissolve silver chloride in a solution of sodium chloride rather than water (just go with me here), will it be more or less soluble? We can either use le Chatelier’s principle to answer this question qualitatively or we can calculate an answer.
Deciding whether a precipitate will form
We can cause a sparingly soluble salt to precipitate out of solution if the product of the concentration of the ions concerned exceeds the Ksp …