Exothermic and Endothermic Reactions 💥
Exothermic is when chemical energy is transferred to heat energy, so the temperature rises.
- In exothermic reactions the bonds are broken between reactant atoms, but less energy is taken in to break the bonds than energy that is given out once the bonds are made, this makes the reaction exothermic as more heat energy is released.
Endothermic is when heat energy is transferred to chemical energy, so the temperature falls.
- In endothermic reactions, the bonds are broken between the reactant atoms, and more energy is taken in to break the bonds than is given out as heat energy when the bonds are made. This makes the reaction endothermic.
Measuring Change🧪
You can measure the energy change in a reaction, from the reactant to the product by following a simple method:
- Place the solution of reactant 1 in an insulated cup. The insulated cup reduces energy transfer in and out the cup.
- Record the temperature of the solution (of reactant 1)
- Add a solution of reactant 2 and stir (or, if it's solid, add a powdered reactant 2) Stirring means the temperature will be evenly distributed without the mixture.
- Wait for the temperature of the new mixture to finish changing. Then, once stable, record the new temperature.
- Follow the equation 'new temperature - old temperature = change in temperature' to work out the difference in energy change during the reaction.
From this, we can clarify whether an experiment is endothermic or exothermic as to if the temperature increases (exothermic) or the temperature decreases (endothermic).
In I/GCSE Chemistry, you may need to know examples of both.
Examples of endothermic experiments: photosynthesis, thermal decomposition, many salts dissolving in water (e.g ammonium nitrate.)
Example of exothermic experiments: combustion, explosions, metal displacement reactions, precipitation reaction and many neutralisation reactions.
Energy Profile Diagrams📉
The making and breaking of bonds in a chemical reaction can be described using an energy profile diagram.
For exothermic reactions, the energy of the products is less than the energy of the reactants. The temperature rise in the experiment comes from energy released.
For endothermic reactions, the energy of the products is more than the energy of the reactants. The temperature fall in the experiment comes from energy being removed from the surroundings.
References: https://blogs.glowscotland.org.uk/gc/public/hchemunit/uploads/sites/5340/2015/05/Picture8.jpg
Drafted by Catrina (Chemistry)