According to kinetic molecular theory, the average kinetic energy of a gas is directly proportional to the temperature in Kelvin. If we have a mixture of gases with different molar masses at a given temperature, the average kinetic energy of each gas will be the same, and lighter gas particles will travel faster, on average. At any given temperature, there's a distribution of velocities for gas particles: some are moving faster, some slower. This distribution is important when discussing Collision Theory and reaction rates. Although there is a distribution of velocities, we can mention the root mean square velocity, which can be regarded as an average velocity. The root mean square velocity is equal to the square root of 3 times the ideal gas law constant, R, times temperature divided by molar mass. We must pay particular attention to units in this equation. The ideal gas law constant has units of joules per mole Kelvin, instead of liter atmospheres per mole Kelvin. Therefore, the constant is 8.314 joules per mole Kelvin. The presence of joules in the ideal gas law constant also implies that our molar mass must be in kilograms per mole, rather than grams per mole, since one joule is equivalent to 1 kilogram meter squared per second squared. Let's practice with our root mean square velocity equation. The problem states, "Calculate the root mean square velocity of gaseous xenon atoms at 215°C." We'll start by using the root mean square velocity equation. In this equation, we need to use the value of the ideal gas law constant with units of joules per mole Kelvin. We also need to convert our temperature to Kelvin and our molar mass from grams per mole to kilograms per mole. By substituting 1 kilogram meter squared per second squared for joules in our ideal gas law constant, we will observe how the units cancel out. Kilograms cancel out, grams cancel out, Kelvin cancels out, moles cancel out, and we are left with units of meters squared per second squared. Since these units are inside the square root, the units for our root mean square velocity are simply meters per second. After completing the calculation, we obtain a value of 304 meters per second.