Thermochemistry studies all the transformations that occur when variations in heat energy occur in a chemical reaction, that is, if it loses or absorbs heat. That is why we say that in many chemical reactions the energy changes that occur are more important than the products that are obtained.
For example, the chemical reactions of combustion in gas stoves and in the internal combustion engines of automobiles, in which the heat obtained is more important than the reaction products. Remember that in combustion processes C02 and water are obtained as a product, but in this case what we obtain in the caloric reaction is more important.
During a chemical reaction, bonds are formed and broken. In the formation of bonds heat is given off, while in the second case it is necessary to apply heat.
When the energy involved in forming the bonds is greater than the energy involved in breaking the bonds that occurs in the reactants, heat is released, the reaction is said to be exothermic. In the opposite case, when the bond breaking energy is higher and the formation energy is lower, the reaction is said to be endothermic.
Let’s explain it in a simpler way. When wood burns, the energy of the system decreases, releasing heat into the environment. That tendency to reach a lower energy is one of the forces that drive all chemical reactions. Those reactions that release energy are known as exothermic reactions.
In an exothermic reaction, the energy of the reactants is relatively high. The products of the reaction have a lower energy. As the reaction proceeds down from high energy to low energy, reactants are converted to products and energy is released from the system.
Almost all chemical reactions tend to release energy, usually in the form of heat. For example, the car is designed to release energy in the form of movement on the road and the heat is from the engine.
In reactions where energy is absorbed, they are called endothermic reactions. In an endothermic reaction, the reaction of the reactants is relatively low and that of the products, on the other hand, is greater. As the reaction progresses from low energy to high energy, reactants are converted to products. In this process energy is absorbed.
Many important reactions absorb energy, plants and animals would not grow without an energy reaction. The reaction for cooking food requires an absorption of energy, therefore it is an endothermic reaction.
But perhaps the differences are best seen by practical experiment.
What do you need to differentiate the endothermic from the exothermic reaction?
Exothermic reaction
- Glycerin.
- Potassium permanganate.
- Dropper.
- Bowl.
Endothermic reaction
- Wax candle.
- Matches.
- 1 Globe.
- Bowl.
- In both experiments you will need safety glasses
Instructions to differentiate the endothermic from the exothermic reaction
Exothermic reaction experiment
- Put on safety glasses.
- Place a cotton ball in the bottom of the container.
- Add a little potassium permanganate to it.
- Use an eyedropper to catch some glycerin.
- Drop a couple of drops of glycerin into the potassium permanganate and stand aside immediately.
- Watch as smoke begins to rise, and then catches fire. The flame soon burns out as it releases the heat.
- By mixing both components, a reaction is generated in the form of heat, causing the fire.
Endothermic reaction experiment
- Blow up two balloons.
- Place a candle in a container.
- Light the candle with a match.
- Pour some wax into the container to hold the candle.
- Place the balloon on top of the candle, so that it is upright.
- Bring it closer to touch the flame, but without putting it out.
- This one will not explode and it will burn at the base because it is absorbing the heat.
Differences
- Exothermic reaction
- Release energy.
- The energy of the reactants is high.
- When the chemical reaction occurs, the energy of the products is low.
- Endothermic reaction
- Absorb energy
- The energy of the reactants is low.
- After the chemical reaction, the energy of the final products is high, that is, they have much more energy than the starting molecules.
Tips to differentiate the endothermic reaction from the exothermic
- When carrying out these experiments it is advisable to be supervised by an adult.
- If you shake the balloon or approach it from the side, it will surely burst. Approach it from above as if it were a pot that is heating up food.
- If despite these differences, you still have doubts about which is which, you can always go to the etymology, that is, to the origin of the word. The term thermal means heat or relative to heat. In this case, it is the heat that will release the energy and cause a reaction. On the other hand, try to remember that “exo” means outwards, therefore it releases energy. And, for its part, “endo” is inward, which implies that it absorbs energy.