A Closer Look at the First Law

Remember the first law of thermodynamics? It described the conservation of energy. When you have a system and it changes, there are four ways it can change its energy. We'll talk about those four ways of changing energy in this section.

Four Thermodynamic Systems

Adiabatic describes a system that changes with no transfer of heat in or out. If a system expands adiabatically, then the internal energy (heat) of the system usually decreases. This is because you did some work to expand the system, and that had to come from the heat energy of the system (since no heat energy can enter the system).

The second type of system is isovolumic. You can probably see the term 'volum' in there. Iso usually stands for constant. Put them together and you get a system that changes, but the volume stays constant. These types of changes do not produce any work on the environment.

The third type of system is isobaric. You've seen the prefix iso before, and the suffix baric refers to pressure. This system changes but keeps a constant pressure. All of the change is in the volume of gas in the system. As you blow air into a balloon, the volume will increase, but the pressure will stay the same. As energy is put into the system, temperature or volume may increase (or both), but there will be no increase in temperature.

The fourth type of system is isothermal. One last iso prefix, and the suffix is now thermal. We're talking about systems that change in every way but their temperature. You would say that these systems are in thermal equilibrium. You would see that the pressure and volume change. As energy is put in the system, the pressure or volume will increase (or both), but there will be no increase in temperature.

Next page on thermodynamics and heat.
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