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# Thermochemistry

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Author: Christene Lohse

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Tutorial

## Specific Heat

Specific heat is the amount of heat required to raise one gram of any substance one degree Celsius or Kelvin. The formula for specific heat is the amount of heat absorbed or released = mass x specific heat x change in temperature.

## Specific Heat Guided Notes

Fill in notes for Specific Heat Video

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Source: C. Lohse

## Enthalpy

Enthalpy is the heat content of a system at constant pressure, but chemists almost always talk about change in enthalpy rather than total energy. Endothermic reactions have positive changes in enthalpy while exothermic reactions have negative changes in enthalpy.

## Thermochemical Equations

Thermochemical equations are balanced chemical equations that include the physical states of all reactants and products and the energy change. If energy is a reactant, the reaction is endothermic but if energy is a product, the reaction is exothermic.

## Hess's Law

Hess's Law states that the energy of a chemical reaction is the same regardless of the number of steps needed or the reaction mechanism. Hess's law is directly related to the law of conservation of energy.

## Heat of Fusion - Heat of Vaporization

Heat of fusion is the energy needed for one gram of a solid to melt without any change in temperature. Heat of vaporization is the energy needed for one gram of a liquid to vaporize (boil) without a change in pressure. These energies are needed to break apart the intermolecular forces holding the solid or liquid together as it enters a less dense state of matter.

## Heat of Formation

Heat of formation is the change in enthalpy when one mole of a compound is formed at 25° Celsius and 1 atm from its elements. Heat of formation has been measured in labs and recorded so that we can look it up when we need it.

of

Source: C. Lohse