...When she got to Enthalpy, she cried out, "Please halp me!

Enthalpy is "heat into" - a measure of the heat change in a chemical or physical reaction

delta H = heat change heat change heat change heat change heat change heat change... don't forget

In Summary
:
During a chemical reaction, energy is needed to break the bonds between atoms. As new
bonds form, energy is produced. The difference between the energy required and the 
energy produced is called the heat of reaction. heat change heat change heat change That energy difference is usually manifested in a temperature change.

If, as is the usual case, more energy is produced than is required, the excess energy is
given off as heat. This heat causes the temperature of the chemicals, container, and
surroundings to increase. A reaction of this type is called exothermic.

There are some reactions that will proceed even though more energy is required than is
produced. This type of reaction is called endothermic and is characterized by a decrease
in the temperature of the chemicals, container, and surroundings.

Chemists measure the heat of reactions with calorimeters. The energy, as heat, is
absorbed by water in the calorimeter. The difference in the temperature of the water before and after the reaction is used to calculate the heat of reaction. The calorimeter is
insulated to prevent heat exchange with the surroundings. The heat of the reaction is then
equal to the heat absorbed by water and the calorimeter.

Yesterday we attempted to determine how much heat went into our calorimeters.  Since we got such divergent results, perhaps we should check our math.  I did the lab in my kitchen and got a specific heat of the calorimeter of 63 J/degree Celcius.  Here is my data table:

Tinitial/cold = 13 degrees C
Thot = 66 degrees C
Tave = 39.5 degrees C
Tmix = 37.5 degrees C
qwater = (200g)(4.184)(37.5-39.5 C) = - 1673 joules
q water = - q cal ("The heat gained by the calorimeter is equal to that lost by the water, but opposite in sign.") 
q cal = 1673
C cal = 1673 / 39.5 -13  = 63 J/ Celsius)
q is "energy transferred as heat" and you might remember q as the quantity of heat, since it is measured in joules.

Are there other sources of error, perhaps?  Did the thermometer finish rising/falling, or perhaps too much heat was lost because we did not use a lid?   Any other ideas?
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So here's more math - Enthalpy Stoichiometry - and here's a teacher explaining: (the first 8 minutes will help you on this worksheet, so after 8 minutes please stop the video and do the worksheet >>answers at the end of the blog. Correct me if I'm wrong.)  Also, watch with pencil and paper in hand, and do the math along with the teacher.

Finish watching the video, and then work on this worksheet Enthalpy Calorimetry, problems 1,3,5 only.  All these problems assume no heat is lost to the calorimeter, so the simple equation to use is q=mcAT (I think) also remembering that deltaH=-q (sorry, the blog has no Greek letters to use, that I know about) 

(you may notice a discrepance in the signs of delta H) 

[nswers to follow]>>> Enthalpy Stoichiometry  Enthalpy Calorimetry