Curriculum Portal

neurologyYou need to know

• An exothermic reaction transfers energy to the surroundings, so the temperature of the surroundings increases.
• An endothermic reaction takes in energy from the surroundings, so the temperature of the surroundings decreases.
• The surroundings are everything outside the reacting chemicals, such as the solution, beaker, air, or thermometer.
• A reaction is identified as exothermic if the measured temperature of the surroundings rises during the reaction.
• A reaction is identified as endothermic if the measured temperature of the surroundings falls during the reaction.
• In an exothermic reaction, the products have less energy than the reactants.
• In an endothermic reaction, the products have more energy than the reactants.
• The overall energy change is the difference between the energy of the reactants and the energy of the products.
• For an exothermic reaction, the overall energy change is negative because energy is transferred from the chemicals to the surroundings.
• For an endothermic reaction, the overall energy change is positive because energy is transferred from the surroundings to the chemicals.
• Activation energy is the minimum energy needed for particles to react when they collide.
• A reaction profile, or energy level diagram, shows the energy of reactants and products as the reaction progresses.
• In a reaction profile, the activation energy is shown as the energy difference from the reactants to the highest point of the curve.
• In an exothermic reaction profile, the reactants are drawn at a higher energy level than the products.
• In an endothermic reaction profile, the reactants are drawn at a lower energy level than the products.
• Useful applications of exothermic reactions include hand warmers and self-heating cans because they release heat energy.
• Useful applications of endothermic reactions include sports injury cold packs because they take in heat energy from the surroundings.

• Identify a reaction as exothermic or endothermic from temperature data by deciding whether the temperature of the surroundings increases or decreases.
• Draw an exothermic reaction profile with reactants above products, a curved pathway, labelled activation energy, and a negative overall energy change.
• Draw an endothermic reaction profile with reactants below products, a curved pathway, labelled activation energy, and a positive overall energy change.
• Label the activation energy on a reaction profile as the energy rise from the reactants to the highest point of the curve.
• Label the overall energy change on a reaction profile as the energy difference between the reactants and products.
• Use a reaction profile to classify a reaction as exothermic or endothermic by comparing the relative energies of reactants and products.
• Evaluate an application of an exothermic or endothermic reaction by linking the energy transfer to its usefulness, risks, and practical limitations.