Pressure and Temperature

Based on what we have learned about the effect of temperature on gas particle motion, we know that as temperature increases, the particles in a gas sample will tend to move more quickly. This means that the particles will collide with the container walls more frequently at a higher temperature. These collisions are also more forceful, since the particles are moving more quickly on average (review the physics concept of impulse to see why). If the container volume is kept constant, pressure of a gas will increase as the temperature increases.

This figure shows a pair of pistons and cylinders. the piston is positioned for the first cylinder so that just over half of the available volume contains 6 purple spheres with trails behind them. The trails indicate movement. Orange dashes extend from the interior surface of the cylinder where the spheres have collided. This cylinder is labeled, “Baseline.” In the second cylinder, the piston is in the same position, and the label, “Heat” is indicated in red capitalized text. Four red arrows with wavy stems are pointing upward to the base of the cylinder. The six purple spheres have longer trails behind them and the number of orange dashes indicating points of collision with the container walls has increased. A rectangle beneath the diagram states, “Temperature increased, Volume constant equals Increased pressure.”
When gas temperature increases, gas pressure increases due to increased force and frequency of molecular collisions.

If the container is allowed to expand (maintaining a constant pressure instead of a constant volume), then the container will expand because of these increased collisions. This explains why the contents of a hot-air balloon expand when heated, as seen in the chapter intro.