chem paper 1 past paper

how to tell if something is polar

1- EN difference = polar bond

2- bond dipoles = cancel out if symmetrical, if asymmetrical, dipoles do not cancel out (no NET difference)

writing equations for catalysts

e.g.

1- find what is oxidised and reduced (S2O8 is reduced, I is oxidised)

2- Fe²⁺ will get oxidised by S₂O₈²—→ 2SO₄^2- + Fe³⁺

3- Fe³⁺ will get reduced by 2I^- —> I₂ + Fe²⁺

The answer is C - because Oxygen exists as O₂ in standard state

ΔH -ve effect on temperature

releases energy (exo), temperature increases

-ve ΔH

exo, releases temp to surroundings

+ve ΔH

endo, absorbs heat energy from surroundings

why is ΔH_neut smaller for weaker acids

partially dissociates in solution (add equation)

some energy is needed to break O-H bonds to release H⁺ ions

enthalpy change of neutralisation includes the enthalpy of dissociation of weak acid so it is less exo