MYP Chemistry: Exothermic & Endothermic Reactions FAQ

You need to link three things: energy transfer direction, temperature change, and bond breaking/forming. Exothermic reactions release energy to the surroundings (temperature rises); endothermic reactions absorb energy from the surroundings (temperature falls). MYP examiners under Criterion A expect you to explain this using particle-level bond energy, not just 'hot' or 'cold'.

An exothermic reaction releases more energy forming new bonds than it took to break the old ones, so the surroundings warm up — combustion is the classic example. An endothermic reaction needs more energy to break bonds than forming new ones gives back, so the surroundings cool — dissolving ammonium nitrate is the standard MYP demo.

Measure temperature before and after mixing with a thermometer or data logger. A rise above the starting temperature means exothermic; a drop means endothermic. In MYP labs you'll usually record this in a table and calculate the temperature change (final minus initial) as your key result.

Combustion, neutralisation, and respiration are classic exothermic reactions you'll meet in MYP Chemistry. Photosynthesis, thermal decomposition of calcium carbonate, and dissolving ammonium nitrate in water are the standard endothermic examples. Knowing at least two of each by name helps in short-answer questions asking you to 'identify' or 'state' an example.

Energy change equals energy absorbed breaking bonds in reactants minus energy released forming bonds in products. If breaking takes more than forming gives back, the reaction is endothermic (positive value); if forming releases more, it's exothermic (negative value). Bond energies are usually given in kJ per mole.

An energy profile diagram plots energy on the vertical axis against reaction progress on the horizontal axis, showing reactants, an activation energy hump, and products. In an exothermic reaction, products sit lower than reactants; in an endothermic reaction, products sit higher — the vertical gap between them represents the overall energy change.

Both processes happen, but they don't cancel out evenly. Breaking bonds always absorbs energy — that's true in every reaction. What makes a reaction exothermic is that forming the new bonds in the products releases more energy than breaking the old bonds required, so the surplus escapes as heat into the surroundings.

This topic sits mainly under MYP Sciences Criterion A (Knowing and Understanding) and Criterion C (Processing and Evaluating) when it appears in practical investigations. You'll be asked to explain energy transfer using scientific vocabulary, interpret temperature-change data, and sometimes sketch or interpret an energy profile diagram.

The most frequent ones are 'state', 'identify', 'explain', and 'describe'. 'State' or 'identify' wants a short factual answer (e.g. 'exothermic'); 'explain' demands the bond-energy reasoning behind it; 'describe' asks you to detail what happens (temperature rises, bonds form) without necessarily justifying why.

The biggest one: saying 'endothermic reactions don't need energy to break bonds.' Every reaction needs energy to break bonds — that's not what makes it endothermic. It's endothermic because breaking bonds costs more energy than forming the new ones returns, so net energy is drawn in from the surroundings, not because bond-breaking itself is unique to it.

MYP focuses on qualitative understanding — temperature change, bond energy reasoning, and energy profile diagrams. DP Chemistry (first exams 2025) goes further with enthalpy change (ΔH), Hess's Law calculations, and calorimetry data analysis at both SL and HL. The MYP groundwork on bond energy directly feeds into DP's quantitative thermochemistry.

The most effective home revision combines short practice questions with a clear set of notes covering bond energy, energy profile diagrams, and command-term practice. On RevisionPrep, MYP Chemistry Revision Notes and Topical Worksheets cover this exact unit with worked examples and practice questions matched to Criterion A and C style tasks.