As early as middle school, students are introduced to the three different states of matter. By the time they reach college, they can easily recognize and identify if a material is a solid, liquid or gas. We help them understand the molecular interactions and energy requirements needed to exist in a given state. One of the major differences between gases and liquids or solids is that the volume of a gaseous sample varies to a greater extent when pressure or temperature is changed. Solids and liquids are affected by temperature and pressure, but the magnitude of the volume change is comparatively very small. We don’t have our students track either temperature or pressure when determining density of a solid or liquid because within the limits of precision of their measurements, the same densities are obtained regardless of slight differences in laboratory conditions. However, as your students will observe when carrying out experiments involving gases, the density, volume or pressure is significantly more sensitive to changes in their surroundings.
There are actually four variables associated with the study of gases: (1) pressure, P, defined as the force exerted by the gas per unit area; (2) temperature, T, a measure of the average kinetic energy of the gas molecules; (3) volume, V, the amount of space occupied by the gas; and (4) the number of molecules (in terms of moles), n, of the gas present. The dependence of these variables on one another can be visualized by holding two variables constant, changing a third variable and visualizing the effect of this change on the fourth variable. This leads to six important relationships discussed below. There is also a fifth term R, which is called the gas constant, and can be calculated by measuring the other four variables in the relationship PV = nRT, the equation for the ideal gas law. With MicroLAB, your students can easily collect and analyze data to visualize how many aspects of this key relationship.