Wednesday, February 23, 2011

Let it be, and learn enthalpy!!!!!!

Oh hello there, it is so nice to see you : )

Guess what we're learning about today? Starts with enthalpy...YESS ENTHALPY (Mr. Hogaboam joke)

Now, in order to actually succeed in learning this foreign topic, I must tell you what enthalpy actually MEANS. Enthalpy, H, is the HEAT contained in a system.

ΔH = the change in enthalpy during a reaction a.k.a kJ/mol

The equation for the total change in enthalpy is:
ΔH = HProduct - HReactant
             HReactant = the heat energy contained in the reactant
          HProduct = the heat energy contained in the product

Now I bet you guys are just dying and so gosh darn excited to move on that you'd fly off a bridge. Well this is your lucky day!

Let us move on to exothermic and endothermic reactions shall we?
An EXOTHERMIC reaction GIVES OFF heat to its surroundings
A trick to remember this is: Heat EXits from the reactants

An ENDOTHERMICreaction ABSORBS heat from its surroundings
A trick to remember this is: Heat ENters the reaction


Energy of the activated complex = potential energy of the "transition state" between reactants and products
Activation Energy (Ea) = the energy that must be added to get the reaction to rpogress (reactants to activated complex)

Lets start with some example equations!!! : D
******Remember, when Kj is on the left side of the equation, it is endothermic and positive. When kJ is on the right side of the equation, it is exothermic and negative*****

Ex/ For the following reaction, calculate the energy released when 1.56 moles of H2O is produced?
CH4 + 2 O2 ----> CO2 + 2 H2O + 918kJ

1.56 mol H2O x   -918 kJ    = 716.04 kJ energy released = 716 kJ or -716kJ
                           2 mol  H2O

Ex/ Using CH4 + 2 O2 ----> CO2 + 2 H2O + 918kJ again, how many grams of CO2 would be needed to produce 2300 kJ of energy?

-2300 kJ x 1 mol CO2  x 44.0g CO2  = 110.2396514g CO2 = 110g CO2
                          - 918 kJ        1 mol CO2

If you still don't understand after my BEAUTIFUL explanatin, you can go to this video to learn what I just said again : )

Lastly, I'll just put in a not so funny joke and hopefully you'll get it : )
This was sent in to us by Robert L. LaDuca (well not really I just found it)

"Yesterday when talking about energy units/enthalpy I drew a man, woman, and child on the board. I put a "J" on each of them. Then I kept on going,without paying it any attention. I let them figure it out, a minute or so later got groans and laughter. Yup, the "Family Joule". ;)"

haw haw haw haw haw haw. Yea this is only funny if you've watched the show "Family Jewels" starring Gene Simmons and his family (wife Shannon Tweed and their kids Nick and Sophie). OHH NOW YOU GET IT? ;)

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,

Friday, February 4, 2011

Lab of Joy

Hello all. Today in class, we all performed a lab. If you are a confused soul who has no idea what I'm talking about- refer to lab 5B (page. 52 in your lab text book).

Anyways, this lab was all about seeing all the different types of chemical reactions. These exist in four main categories:

-Synthesis (A + B -> AB)
-Decomposition (AB -> A + B)
-Single Replacement (AB + X -> A + XB) *switch non-metals with non-metals, or metals with metals
-Double Replacement (AB + XY -> AY + XB)

There were seven unique reactions for you to test out in this lab, and hopefully you all recorded your results on the chart that was supposed to be copied and completed. This lab should have expanded your knowledge with reactions, because you were actually able to see what it looked like.

All 4 types of reactions listed above were present in the lab, and if you did not realize it, your head must've been in the clouds. Be sure to reread the lab and make sure you understand what you were doing step by step.

You should now be more comfortable working with lab equipment and various chemicals + solids. If you didn't dispose of your waste properly (down the sink with lots of water, or in the special waste containers) remember to keep that in mind for our next lab.

The lab write up is due next class, so be sure to have that completed and ready to go. A thorough understanding of chemical reactions in general is needed to answer the required lab questions.

Good luck!

If this happened during your lab, you did it wrong. :)