Endothermic/Exothermic Reactions

All chemical reactions involve changes in energy. Some reactions release energy (exothermic) and others absorb it (endothermic).

Here are some points to remember:

• If a reaction takes less energy to break bonds than it gives off to form bonds, it is exothermic.
• Enthalpy, represented by H, is the heat contained in the system

Okay, now lets get down to the good stuff! Energy diagrams! Now I am a proud graph hater, but it can be straightforward if you pay attention to all the different names. First, lets learn them:

• Energy of reactants = total potential energy of all reactants in the reaction
• Energy of products = total potential energy of all products in the reaction
• Energy of the activated complex = potential energy of the "transition state" between reactants and products.
• Activation energy = the energy that must be added to get the reaction to progress (reactants to activated complex)
• Delta H (there is no delta sign on this computer, sorry!) = change in potential energy during the reaction.

And what is chemistry without formulas? Here are some to keep in mind:

Delta H: Energy of products - energy of the reactants
Energy of activated complex = energy of reactions + activation energy

If the change in enthalpy is negative, it is exothermic. If it is positive, it is endothermic.

Now, onto the graph.
Label the x axis as the reaction progress. (some unit of time)
Label the y axis Potential Energy in kJs.

Want to see what it all looks like?

From this diagram, you can see everything I just talked about! Notice the labels and try to draw your own!

Here are some videos to help you out!

Endothermic Reactions

Exothermic Reactions

Animation on activation energy