Beryllium Chemists!: EXOTHERMIC AND ENDOTHERMIC REACTIONS! (going into thermodynamics)

Woot! Today's blog is about..... EXO AND ENDOTHERMIC REACTIONS!

Exothermic and endothermic reactions are always there in a chemical reaction! They have to do with the absorption and the releasing of heat or in other words energy.

Exothermic means the release of energy to the suroundings.

Endothermic means the absorbtion of energy from the surroundings.

For example:
The formation of snow in clouds releases energy and are exothermic reactions.
Melting ice absorbs energy and are endothermic reactions.

Furthermore:
Chemical bonds are what holds the molecules together
- If energy is added, it breaks the bonds because there is an increase in kinetic energy.
- If it gives off energy, it joins together and the molecules have little movement.
- more energy to break bonds than it gives off to form bonds = endothermic!
- less energy to break bonds than it gives off to form bonds = exothermic!
- Enthalpy (H) is the heat in the system.

ENERGY DIAGRAMS!!! (shows the change from start to end)
- Reactants start with a certain amount of energy, energy is added to start reaction, and is then released OR absorbed in process.
- Relative amount of energy determines if the reaction is endothermic or exothermic

Things to know about the potential energy graph...
1) Energy of reactants is the total potential energy of all reactants.
2) Energy of products is the total potential energy of all reactants.
3) Energy of activated complex is the potential energy of "transition state" between reactants and products.
4) Activation energy is the energy that must be added to get the reaction to progress (from reactants to activated complex).

Perhaps an analogy may help some understand potential energy diagrams better!
Below, A is the reactant, and the pushing up the hill is the activation energy needed in order for the rock to progress. When it reaches the top of the hill, it is at the potential maximum energy of the transition state before the energy is changed. As A (the rock) rolls down the hill and comes to a stop, it becomes the product (B). Since the end position of the rock is further down from it's origin, then the change in energy is negative. This is an example of an exothermic reaction because the energy in the end is less than at the start, so energy is released.