Exothermic and endothermic reactions common mistakes

Common mistakes

• Misinterpreting temperature change as energy direction

  Students think that a rise in temperature of the surroundings means the reaction is endothermic, and a fall means exothermic.

  Fix itExplain that in an exothermic reaction energy is released to the surroundings, raising their temperature; in an endothermic reaction energy is absorbed from the surroundings, lowering their temperature.

• Misunderstanding Applications

  Students often confuse the applications of exothermic and endothermic reactions, thinking that both types are used for heating.

  Fix itTo fix this, students should study specific examples of each type, such as self-heating cans for exothermic reactions and sports injury packs for endothermic reactions, to understand their distinct uses.

• Measuring Temperature Changes

  Students often forget to account for the initial temperature of the water before adding the reactants, leading to inaccurate measurements of temperature change.

  Fix itAlways record the initial temperature of the water before starting the reaction to ensure accurate calculations of temperature change.

• Misunderstanding the Required Practical

  Students often confuse the variables affecting temperature changes in the required practical, thinking that only one type of reaction (like neutralisation) is investigated.

  Fix itEmphasize that the practical involves multiple types of reactions, including acid plus metal, acid plus carbonate, and displacement reactions, and that each can affect temperature changes.

• Misunderstanding Enthalpy Change

  Students often think that calculating enthalpy change (ΔH) is necessary for all reactions in this section.

  Fix itRemember that for this GCSE section, it is explicitly stated that the calculation of enthalpy change is not required.

• Collision Requirement Misconception

  Students think that any collision between particles will automatically cause a reaction, ignoring the need for sufficient energy and correct orientation.

  Fix itExplain that a reaction only occurs when colliding particles have enough kinetic energy to overcome the activation energy barrier and are properly oriented to form new bonds. Use the concept of activation energy and reaction profiles to illustrate that not all collisions lead to products.

• Misunderstanding Collision Theory

  Students often think that any collision between particles will result in a reaction, without considering the energy involved.

  Fix itEmphasize that for a reaction to occur, particles must collide with sufficient energy, known as activation energy.

• Confusing Activation Energy

  Students often confuse activation energy with the overall energy change of a reaction.

  Fix itRemember that activation energy is the minimum energy required for particles to react, while overall energy change refers to the difference in energy between reactants and products.

• Mislabeling Reaction Profiles

  Students often label the energy change in an exothermic reaction profile incorrectly, indicating that energy is absorbed instead of released.

  Fix itRemember that in an exothermic reaction, energy is released to the surroundings, so the products should be at a lower energy level than the reactants.

• Mislabeling Reaction Profiles

  Students often label the energy change in an endothermic reaction profile incorrectly, indicating it as a decrease instead of an increase.

  Fix itRemember that in an endothermic reaction, the products have more energy than the reactants, so the energy change should be labeled as an increase.