Thermochemistry
[Pages:22]April 30, 2014
Thermochemistry is the study of heat changes (energy!) that accompany chemical reactions and phase changes ? Heat is exchanged between the system and
surroundings
system = part of the universe that contains the reaction or process being studied surroundings = rest of the universe that interacts with the system
April 30, 2014
April 30, 2014
Enthalpy (H) is the heat content of a system at constant pressure. (Enthalpy is potential energy)
Change in enthalpy for a reaction is called the enthalpy (or heat) of reaction ( Hrxn).
Hrxn = Hfinal - Hinitial Hrxn = Hproducts - Hreactants
The second equation shows you how you can think about enthalpy of a reaction as the difference in energy of the products and reactants.
April 30, 2014
Enthalpy
< Energy required to
break bonds
Energy released to form bonds
Reactants
Enreerlegaysiesd
Products
Exothermic Reaction
H Energy required to
break bonds
Energy released to form bonds
Enthalpy
Reactants
Products
Enearbgsyorisbed
Endothermic Reaction
H>0, + H
What happens to the surrounding?
April 30, 2014
Is thi
April 30, 2014
Thermochemical equations: balanced chemical equation that includes the physical states of all reactants and products and the energy change, usually expressed as the change in enthalpy ( H).
Example: CH4(g) + 2O2 (g)
CO2(g) + 2H2O(g) Hrxn= -802.3kJ
April 30, 2014
Coffee cup calorimeter
Bomb calorimeter
Reaction happens in water
-qsystem = qwater
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