Calorimetry Notes

E. Smith
 The accurate and precise measurement of heat change
for chemical and physical processes.
 Calorimeter
 An insulated device used to measure the absorption or
release of heat in a chemical or physical process.
E. Smith
E. Smith
Enthalphy…a Fancy Word for Heat
 For systems with constant pressure, the heat content is
the same as a property called enthalpy (H).
 A change in heat at constant pressure is called a
change in enthalpy (H) of a system.
 At constant pressure
 q = H = C x m x T
E. Smith
Thermochemical Equations
 A thermochemical equation expresses the heat needed
or released in a chemical reaction.
 Example of an exothermic reaction CaO(s) + H2O  Ca(OH)2 (s) + 65.2 kJ
 Or the same equation can be expressed as
CaO(s) + H2O  Ca(OH)2 (s)
E. Smith
H = - 65.2 kJ
Endo- and Exo If the H is negative (-) then the reaction is
 If the H is positive (+) then the reaction is
 Knowing H will allow you to calculate the amount of
heat released or gained in the reaction.
E. Smith
 Gasohol contains ethanol (C2H5OH), which when
burned reacts with excess oxygen to produce CO2 gas
and water vapor. How much heat is released when 12.5
g of ethanol is burned?
 C2H5OH (l) + O2 (g)  CO2 (g) + H2O (g)
 H = -1235 kJ
E. Smith
 First check if the equation is balanced!
 C2H5OH(l) +3O2(g)  2CO2(g) + 3H2O(g)
12.5 g C 2 H 5 OH 
1 mol C 2 H 5 OH
46.0 g C 2 H 5 OH
 1235 kJ
 - 336 kJ
1 mol C 2 H 5 OH
 336 kJ of heat is released when 12.5 grams of C2H5OH
is combusted with an excess of oxygen. The negative
value tells you this is an exothermic reaction!
E. Smith

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