Gas Behavior Lesson 3, Chapter 2

Measuring Gases When working with a gas, it is helpful to know its volume, temperature, and pressure. Gases easily contract or expand to fill it container. Because gas particles move and fill the space available, the volume of a gas is the same as the volume of its container. Temperature is a measure of the average energy of random motion of the particles of a substance. The faster the particles are moving, the greater their energy, and the higher the temperature. Even at average temperatures, the speed of particles of gas are still very fast.

Gas particles constantly collide with one another and with the walls of their container. As a result, the gas pushes on the walls of the container. The pressure of the gas is the force of its outward push divided by the area of the walls of the container. The firmness of a gas-filled object comes from the pressure of the gas.

Pressure and Volume Boyle found that when the pressure of a gas at a constant temperature is increased, the volume of the gas decreases. When the pressure is decreased the volume increases. This is called Boyle’s Law Example: You fill a balloon with a small fraction of helium gas that the balloon can hold. As the balloon rises into the atmosphere, the air pressure around the balloon decreases, but the balloon expands. If the balloon was completely filled before you let it go into the air, it would pop once it got very high.

Pressure and Temperature When the temperature of a gas at a constant volume is increased, the pressure of the gas increases. When the temperature is decreased, the pressure of the gas decreases. Example: An 18-wheel truck needs a lot of air in their tires to support the weight of the vehicle. On long trips, especially in warmer weather, the truck’s tires can become very hot. As the temperature increases, so the does the pressure of the air inside the tire. If the pressure become greater than the tire can handle, the tire will burst.

Volume and Temperature Charles found that when the temperature of a gas is increased at a constant pressure, its volume increases. When the temperature of a gas is decreased at a constant pressure, its volume decreases. The is known as Charles’s Law Example: page 60 in text

Gas filled balloon at room temperature Gas filled balloon lowered into liquid Nitrogen at -196 degrees The balloon shrinks as Gas volume decreases. Before After

When removed from the nitrogen, the gas warms and the balloon starts to expand again. Once the balloon reaches room temperature again, it takes its original shape back