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

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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?

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Is thi

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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

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Coffee cup calorimeter

Bomb calorimeter

Reaction happens in water

-qsystem = qwater

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