WASSCE Chemistry · Paper 1 style

Energy changes

One sample question with the full working. 5 more in the app, with instant feedback and repair sessions for the traps below.

The dissolution of ammonium nitrate in water makes the solution feel cold. The process is

Aexothermic, ΔH positive
Bneither exothermic nor endothermic
Cexothermic, ΔH negative
Dendothermic, ΔH positive

Show the answer and working

Answer: D

Heat is absorbed from the surroundings, so the temperature falls.

Trap A Gets the sign of ΔH backwards: ΔH is measured from the reaction's point of view: heat out → ΔH negative (exothermic, surroundings warm up). With bond energies, ΔH = bonds broken − bonds formed.

Trap B Uses everyday or macroscopic thinking instead of particles: Ask what the particles, ions or electrons are doing. Properties of a substance come from its particles and bonds, not from how it looks or feels.

Trap C Picks a related substance or process with a different role: Learn reagents and processes as one-line 'name → job' cards and contrast neighbours in a table (process | product | catalyst | conditions). Match the job in the stem, not just the topic.

Traps in Energy changes

Gets the sign of ΔH backwards
ΔH is measured from the reaction's point of view: heat out → ΔH negative (exothermic, surroundings warm up). With bond energies, ΔH = bonds broken − bonds formed.
Uses everyday or macroscopic thinking instead of particles
Ask what the particles, ions or electrons are doing. Properties of a substance come from its particles and bonds, not from how it looks or feels.
Picks a related substance or process with a different role
Learn reagents and processes as one-line 'name → job' cards and contrast neighbours in a table (process | product | catalyst | conditions). Match the job in the stem, not just the topic.
Ignores or misapplies a subscript or bracket
A subscript multiplies only the atom before it; a subscript after a bracket multiplies everything inside. Expand the formula into a full atom list before adding masses.
Uses the wrong arithmetic operation
Write the relationship in words before substituting (crystals = solubility at high T − solubility at low T; neutrons = A − Z; three doublings = 2³). Then check the size of the answer.
Reverses a trend, direction or effect
State the rule with its direction before looking at the options (down group 1 reactivity INCREASES; exothermic forward reaction: heating shifts LEFT). An option that is the mirror image of the rule is the trap.
Takes one factor as the whole answer
Ask whether the option is necessary or sufficient. If the stem involves two changes or two conditions, both must appear in the answer.

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