The British thermal unit (Btu) is commonly used in engineering applications. A Btu is defined as the amount of heat required to raise the temperature of 1 lb of water by 1°F. There are __________ joules in one Btu. 1 lb = 453.59 g; °C = (5/9)(°F - 32°); specific heat of H2O (l) = 4.18 J/g-K.

Thermochemistry is the study of heat energy associated with chemical reactions and phase changes.  Thermochemistry involves the following concepts: Heat of reaction: Also known as the enthalpy of reaction, this looks at the overall heat energy that occurs in a reaction. Enthalpy: The heat content of a system. Hess's law: A principle in general chemistry that states that the change in enthalpy for a reaction is independent of path and depends only on initial and final states. Closed system: A thermodynamic system that exchanges neither energy nor matter with its surroundings. A covered... Show more

Thermochemistry is the study of heat energy associated with chemical reactions and phase changes. 

Thermochemistry involves the following concepts:
Heat of reaction: Also known as the enthalpy of reaction, this looks at the overall heat energy that occurs in a reaction.
Enthalpy: The heat content of a system.
Hess's law: A principle in general chemistry that states that the change in enthalpy for a reaction is independent of path and depends only on initial and final states.
Closed system: A thermodynamic system that exchanges neither energy nor matter with its surroundings. A covered pot on the stove is approximately a closed system. 

Thermochemical reactions can be either endothermic or exothermic:
Endothermic reactions: Absorb heat energy.
Exothermic reactions: Evolve heat energy. In exothermic reactions, more energy is released when the bonds are formed in the products than is used to break the bonds in the reactants. 

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