What this practice covers
These questions are drawn from past CIE 9701 Chemistry papers and filtered to chemical energetics. You answer, you find out immediately whether you were right, and you get the reasoning for the correct option and for each distractor. Wrong answers go to a mistakes locker so you can come back to exactly those.
Practice is free. You need an account only so your progress and your mistakes are still there next time.
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What examiners see students get wrong here
These are the errors that cost marks on chemical energetics, taken from our own topic notes. Read them before you practise and you will recognise the traps in the questions.
- Defining lattice energy in the wrong direction, so the sign comes out positive. The syllabus defines it as gaseous ions to solid, which is exothermic.
- Using a bond enthalpy where an enthalpy of atomisation is wanted. Atomisation makes one mole of gaseous atoms, so it is half the bond enthalpy for a diatomic molecule.
- Making the second electron affinity negative. It is endothermic, because the electron is added to a negative ion.
- Forgetting the second ionisation energy in a Born-Haber cycle for a 2+ cation.
- Saying charge and radius affect lattice energy without saying which way, or saying "the lattice energy is bigger" when the value is negative and what is meant is more exothermic.
- Adding the lattice energy to the hydration enthalpies instead of subtracting it in a solution cycle.
- Assuming ΔS is positive for every dissolving process.
- Forgetting to multiply an entropy by its coefficient in the balanced equation.
Revise it first
If any of the above is unfamiliar, work through the notes before practising: Chemical energetics revision notes.