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 of the system usually decreases. It's as if you have a cup of water just out of the tap. You let the cup sit and the water settles down. The big idea to remember is that there is less energy and no transfer of heat.

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 amount of energy changes (an increase or decrease), but the heat just stays inside the system because the volume of the system stays the same.

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 may change but the pressure will stay the same.

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, pressure or volume increase (or both), but there is no increase in temperature.

RELATED LINKS

- Chem4Kids: Reaction Thermodynamics
- Chem4Kids: Changing States of Matter
- Chem4Kids: Catalysts
- Biology4Kids: System Regulation
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- Geography4Kids: Earth Energy
- Geography4Kids: Air Temperature
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