Chapter 3: Solids, Liquids and Gases Section 3: The Behavior of Gases What types of measurements are useful when working with gases? How are the volume, temperature, and pressure of a gas related?

Measuring Gases When working with a gas, it is helpful to know three measures: volume, temperature, and pressure. Let’s think back to Chapter 1 and redefine some of these terms!

Volume Volume is the amount of space that matter fills. Since gas particles move to fill up the space available, the volume of a gas is the same as the volume of it’s container. Units for Volume = cm3, mL, L, etc.

Temperature Temperature is a measure of the average energy of motion of the particles of matter. The faster the particles are moving, the more energy they have, and the higher the temperature they have. Units for temperature = K, °C, °F

Pressure Gas particles are constantly moving and pushing against the walls of their container. The pressure of the gas is the force of its outward push divided by the area of the walls of the container. Units for Pressure = pascals (Pa), or kilopascals (kPa). 1 kPa = 1,000 Pa

WHY? Pressure (continued) The firmness of a gas filled object comes from the pressure of the gas. Example: Air inside a fully pumped basketball has a higher pressure than the air outside, because there is a greater number of gas particles per unit volume inside the ball than in the air outside. WHY? Who knows what would happen if you poked a hole in the basketball?

A Change in Pressure A punctured basketball deflates as gas particles begin to escape. Due to high pressure inside the ball, gas particles hit the inner walls of the ball more often, therefore reach the hole more often and escape. The pressure inside drops until it equals the pressure outside.

Pressure and Volume If temperature is held constant, then gas pressure and volume are inversely proportional to each other. This means as one goes up, the other goes down. Example: If the volume is tripled, pressure would be 1/3 of what is was. This concept is described by Boyle’s Law.

Boyle’s Law As weights are added, the gas particles occupy a smaller volume. The pressure increases.

Graphing Boyle’s Law: This is what a basic graph of Boyle’s Law should look like. It should show a nonlinear trend. At any point on the curve, you should be able to multiply the 2 variables and get the same product. 70 X 20 = 1400 50 X 28 = 1400 This is because the relationship between the 2 variables (Pressure and Volume) is that they are inversely proportional.

Temperature and Volume When pressure remains constant, then temperature and volume are said to be directly proportional to each other. This means that as temperature increases, volume increases. And as temperature decreases, volume decreases. This concept is explained by Charles’ Law.

Charles’ Law When the temperature of a gas increases at constant pressure, its volume increases.

Graphing Charles’ Law: This is what a basic graph of Charles’ Law should look like. The graph should show a linear trend (straight line) that passes through the origin. This is because the relationship between the 2 variables (volume and temperature) is that they are directly proportional to each other.

Pressure and Temperature When the temperature of a gas at constant volume is increased, the pressure of the gas increases. When the temperature is decreased the pressure of the gas decreases. Constant volume means that the gas is in a closed, rigid container.

Pressure and Temperature When a gas is heated, the particles move faster and collide more often with each other and with the walls of their container. The pressure of the gas increases.