Endothermic Vs. Exothermic

Hey there!

Alright so today in class we picked up some papers, they are The Heat of Combustion Lab, the Energy Diagram Worksheet, then finally Energy and Reactions. We also picked up some notes but we didn't go over them in class, instead Mr. Lieberman talked to us about Endothermic and Exothermic graphs. The Exothermic graph looks like this:

The reason why the products are lower is beacuse Exo means out, so the reactants lose energy. The reaction Coordinate is just the run time.

The Endothermic Graph looks like this: (Ignore the Delta E it's supposed to be Delta H)

The reason why the products are higher is because Endo means in, so the reactants gain energy. The reaction is the run time. E is the amount of energy. So I bet you're wondering about the Ea and the Delta H right about now. So I'll explain them to you.

Ea stands for Activation enery. That means the energy used to create the product.

Delta H stands for the energy released. That is the energy that was released by the reactant to make the product. The H stands for Enthalpy. The Delta H and q have equal values. So Delta H=q. The q stands for heat gained (or lost). But we cannot just switch q out for Delta H in the formula (to the right)

Here's the reason why.

q can be determined by an experiment: get the mass the specific heat and the temperature change and you can find q. But Delta H is theoretical, and q is actual. So you cannot find Delta H through an experiment. But one way you can find Delta t is the products (on graph) minus the reactants (on graph) no matter which type of transfer there is, it is always products minus reactants.

Mr. Lieberman showed the class some magnets today and was asking about the energy transfer as they connect and as they detach. What do you think? When put together is the energy absorbed or released, and when detached is the energy absorbed or released? How can you tell? I won't answer, just think about it.

Well I lied earlier when I said we didn't go over the notes... We went over one slide but we didn't even look at it on the projector screen. It was the last slide, the sample problem. All we did was copy down two ways to write the change of energy using a methane reaction. Here are the two ways:

(there's supposed to be a space between the H2O and Delta H).

The first way has the equation that was the reaction and product and to the right of the equation was the release of energy. Since the release had a negative effect (the Methane lost 890KJ) the number is a negative. But if instead of losing 890 it gained it, then the number would be positive.

The second way is to add the energy release directly into the problem. The + 890 KJ is just saying the reaction included 890 KJ of energy released.

The pre-lab for Heat if Combustion is due tomorrow, also there is a web assign due tomorrow as well. The worksheets are, like always, due on the last day of the chapter, which this time is the day of the quiz (1/11/11).

Have you figured out the questions I asked earlier? No? Google it!

The next scribe is...Lauren C.!!!! YAY!

Good Luck.

P.S. This took me a lot of time to work out (I had to redo a ton of stuff) So please like it!