Saturday, February 19, 2011

Energy. Bow chicka wow wow

Despite the fact that our title here today lacks flamboyancy, this topic definitely does not. While the concept is generally simple, occasionally you may get thrown away by your stupidity. Jokes.

In general, there are two types of reactions: An exothermic and an endothermic reaction. I understand you are now facing the conundrum, but do not fear, MJH is here!

The best and easiest interpretation of energy is thinking of it as heat. Heat is a form of energy that is most commonly referred to in reactions.

An exothermic reaction is a reaction that releases energy. Therefore, it breaks bonds. The burning of firewood is an example, because it gives off heat into the atmosphere.

An endothermic reaction is a reaction that absorbs energy. Therefore, it combines bonds. The melting of ice is an example of an endothermic reaction, because you are adding heat to the ice cube, making it absorb the heat and melt.

Comrende? I hope y'all said si. Now here is where we get funky. Here is an example of an energy diagram.

This here, my beautiful friends is an energy diagram for an exothermic reaction. This looks very complicated, but after we explain this to you, we guarantee you will be well on your path to enlightenment.

First off, your y-axis is always your potential energy (in kJ) and your x-axis is your time elapsed. In this diagram it says "reaction pathway" but in our cases, it would be the time in seconds. You first start off with your reactants. Your reactants will always start and the end of your graph will be your products. Okay, so review what we just learnt:
Step 1: Label reactants and products. Reactants first, then products. This should be pretty straightforward.

The top of the little gooseneck that we have is our activated complex. Labelled on the graph above, is Ea. That is the activation energy. The activation energy is basically how much energy you need in order to get the reaction up and going. Review time once again:
Step 2: Label your activated complex whatever it is.

The triangle with the H is "delta ayche". Basically the change in energy/heat. For those of you who take physics, please do not be confused with delta Q. The scientific name for it is enthalpy. Which is basically the change in energy. They just simply had to give it a fancy schmancy name for it. Typical chemists.
Delta H can be calculated using the following formula: Eproducts - Ereactants= Delta H.
This is awfully just logical, however please do not be confused with difference.

If delta H is positive then the reaction is endothermic, since there would be more energy, therefore, the reaction would be absorbing energy.
If delta H is negative, then the reaction is exothermic, since the reactant would be losing energy, therefore the reaction would be releasing energy in some form or another.

Ms Chen said apparently next class we're going to be writing equations using this... Oh joy. In the meantime, please just enjoy this video.

This is an example of an exothermic reaction since it is giving off heat.
And here is a rather cool, if I may say so myself, example of an endothermic reaction.

Ps; I know y'all miss our videos, but since life has been taking a toll on us lately--yes, we're making it personal--it has been hard to find the time to make WONDERFUL and INTERACTIVE chemistry videos. But please to stay tuned, as Savannah, Harriet, and Jia Liu will be back in no time.

Sorry for the inconvenience caused,

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