According to Boyle's Law, when temperature and moles of gas are constant, volume and pressure are inversely related. So if we double the pressure on a gas, we will halve the volume of the gas. The kinetic molecular theory attempts to explain this relationship. The size of a gas particle is negligibly small compared to the volume it occupies, and pressure is caused by the collisions of gas particles with a surface. If the temperature remains constant, then the average kinetic energy (and thus the average speed) of the gas particles remains the same. So if we decrease the volume by a factor of two, but keep the same number of gas particles, there will be more collisions with the walls of the container, resulting in an increase in pressure. We can represent this inverse proportionality mathematically using the equation: P1 V1 = P2 V2, where P is pressure and V is volume. Let's practice using Boyle's Law. The problem reads, "You inflate a balloon to a volume of 2400 milliliters at the surface of the ocean (at sea level). You bring the balloon to a depth of 30 meters, where the pressure increases to 4 atmospheres. What will the volume of the balloon be assuming a constant temperature?" We'll start with the equation P1 V1 = P2 V2. We want to rearrange the equation to solve for volume 2, which equals P1 V1 / P2. At sea level, the pressure should be one atmosphere, and the volume of the balloon is 2400 milliliters. P2 is 4 atmospheres. Our units of atmospheres cancel out, and we're left with units of milliliters. Solving the equation, we get a volume of 600 milliliters for the balloon.