2
Work, Heat, and Energy:
The First Law of Thermodynamics
PRINCIPAL FACTS AND IDEAS
- Thermodynamics is based on empirical laws.
- The first law of thermodynamics asserts that the internal energyUis a
state function if
∆Uq+w
whereqis an amount of heat transferred to the system andwis an amount
of work done on the system.
- Heat is one way of transferring energy.
- Work is another way of transferring energy.
- The first law of thermodynamics provides the means to calculate amounts
of work and heat transferred in various processes, including adiabatic
processes.
- The enthalpy is a state function whose change in a constant-pressure
process is equal to the amount of heat transferred to the system in the
process.
- The enthalpy change of a chemical reaction can be calculated from the
enthalpy changes of formation of all products and reactants.
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