Enthalpy is a measure of the total energy of a thermodynamic system. The unit for these calculations is H or ΔH for the change in enthalpy. It is expressed as KJ/mole.
An example of these reactions would be the combustion of propane:
C3H8(g) + 5O2(g) ---> 3CO2(g) + 4H2O(l) - 2220 KJ
ΔH in this reaction can be expressed:
-2220 KJ
1 mol C3H8
-2220 KJ = -444 KJ
5 mol O2 1 mol O2
-2220 KJ OR -740 KJ
3 mol CO2 1 mol CO2
-2220 KJ OR -550 KJ
4 mol H2O 1 mol H2O
Ex. Calculate the energy released when 0.25 moles of H2O is produced.
0.25 moles H2O x -550 KJ = -137.5 KJ -> 1.4 x 10^2 KJ
1 mol H2O
Ex. How man moles of C3H8 is needed to produce 2500 KJ of energy?
2500 KJ x 1 mol C3H8 = -1.126 KJ -> 1.2 moles of C3H8
-2220 KJ
A worksheet:http://www.docstoc.com/docs/70077972/Empathy-Worksheet
Video of enthalpy calculations:
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