Exothermic and endothermic reactions common mistakes

Common mistakes

• Misunderstanding Energy Conservation

  Students often think that energy is lost during chemical reactions instead of being conserved.

  Fix itEmphasize that energy is conserved in chemical reactions; it can change forms but is never lost.

• Confusing Energy Transfer

  Students often state that the products of an exothermic reaction have more energy than the reactants.

  Fix itRemember that in an exothermic reaction, energy is transferred to the surroundings, resulting in products that have less energy than the reactants.

• Misunderstanding Exothermic Reactions

  Students often think that exothermic reactions absorb energy from the surroundings instead of transferring it.

  Fix itRemember that an exothermic reaction is defined as one that transfers energy to the surroundings, resulting in a release of heat.

• Surroundings temperature change

  Students think the temperature of the surroundings decreases during an exothermic reaction

  Fix itExplain that in an exothermic reaction energy is released to the surroundings, so their temperature rises

• Misidentifying a neutralisation as endothermic

  Students often think that a neutralisation reaction, such as mixing an acid with a base, absorbs heat and is therefore endothermic.

  Fix itExplain that neutralisation releases heat to the surroundings, making it an exothermic reaction, and that the temperature of the solution rises during the process.

• Misunderstanding Everyday Uses

  Students often confuse the uses of exothermic reactions, thinking that self-heating cans and hand warmers are examples of endothermic reactions.

  Fix itRemember that exothermic reactions release energy to the surroundings, which is why hand warmers and self-heating cans generate heat.

• Misidentifying the source of energy

  Students often think an endothermic reaction takes energy from the reactants rather than from the surroundings

  Fix itClarify that in an endothermic reaction the reactants absorb energy that comes from the surroundings, so the surroundings lose energy and cool down

• Misunderstanding Temperature Change

  Students often think that the temperature of the surroundings increases during an endothermic reaction.

  Fix itRemember that in an endothermic reaction, energy is absorbed from the surroundings, causing the temperature of the surroundings to decrease.

• Confusing Endothermic Reactions

  Students often confuse thermal decomposition with exothermic reactions, thinking they release energy instead of absorbing it.

  Fix itRemember that thermal decomposition is an endothermic reaction that takes in energy from the surroundings, while exothermic reactions release energy.

• Misidentifying the temperature change in sports injury packs

  Students think sports injury packs warm the surroundings because they feel hot

  Fix itExplain that sports injury packs are endothermic; they absorb heat from the surroundings, so the pack feels cold and the surrounding temperature falls