http://www.ck12.org Chapter 14. Thermodynamics
14.2 First Law of Thermodynamics
Objectives
The student will:
- Describe the First Law of Thermodynamics.
- Solve problems using the First Law of Thermodynamics.
Vocabulary
- adiabatic process:A thermodynamic process in which no heat enters or leaves the system.
- Heat Reservoir
- isobaric process:A thermodynamic process that takes place at constant pressure.
- isochoric process:A thermodynamic process that takes place at constant volume, also known as an isovolu-
metric process. - isothermal process:A thermodynamic process that takes place at constant temperature.
Introduction
The word thermodynamics puts together “thermo-”, meaning heat, and “dynamics”, meaning change.
Thermodynamics is the study of processes by which energy is transferred by heat and work.
When studying thermodynamics, we will often refer to “the system," which is often a gas within some sort of
container. There are three types of systems: isolated, closed, and open. Mass and energy cannot enter or leave an
isolated system. Only energy may enter or leave a closed system. Both mass and energy may enter or leave an open
system.
Heat as explained earlier is the transfer of energy due to a temperature difference. Work is a transfer of energy when
there is no temperature difference.
James Joule showed that mechanical work was equivalent to heat. A given amount of work done on a system could
raise the temperature of the system the same as if a flame had transferred energy to the system (as if the system
was heated). But we know from the Kinetic Theory that when energy is transferred to a system, the molecules gain
kinetic energy. If we restrict our attention to ideal gases, then the sum of the kinetic energy of the molecules is equal
to the internal energy of the substance.