What is being taught lesson by lesson:
- Endothermic and Exothermic reactions.
- Investigating temperature changes in reactions (required practical). Use the equation from physics (specific heat capacity).
- Reaction profiles.
- Bond energy.
Key Terms for this topic (Tier 3 vocabulary)
Exothermic – endothermic – reaction profile – activation energy – bond energy.
What everyone needs to know:
In a chemical reaction, energy is conserved. The energy before is equal to the amount of energy afterwards. Energy is stored in the bonds between atoms in a molecule.
Exothermic reactions release heat that was stored in bonds to the atmosphere (gets hotter). – Combustion, oxidation, neutralisation. Used in handwarmers.
Endothermic reactions absorb heat from the surroundings and store it in bonds (gets colder). – Thermal decomposition. Used in sports injury cold packs.
You need to be able to tell the difference based on experimental results and categorise exothermic or endothermic. You can then suggest uses for these reactions.
Required practical 10 – Investigate the variables affecting temperature changes in reactions like neutralisations.
You need to be able to draw reaction profiles for both endothermic and exothermic reactions. Ensure that you can label activation energy (minimum amount of energy needed to start a reaction off), reactants and products. Also, identify the overall energy change (difference in height between reactants and products.
Extra topics needed for the Higher papers:
Bond enthalpy – in a reaction, energy is needed to break the bonds between the reactants. Energy is then released when bonds are formed making the products.
Given data about the energy required to break bonds (bond energy), you should be able to calculate the energy change in a reaction and say if it is exothermic (-) or endothermic (+).