The Behavior of Gases

About Gases Remember that particles in gases are the fastest-moving and most spread out of all the regular states of matter (all except plasma). . . -- therefore, gas particles have a lot of energy Additionally, the definition of a gas is the state of matter with no definite shape or volume Because of the nature of particles and the definition of a gas, gases can be easily expanded and compressed to fill whatever container they are in. Therefore, there are three properties we need to measure when we examine gases. . . -- they are volume, temperature, and pressure

Volume of a Gas The volume of a gas is the exact same as the volume of the container that the gas is in. . . -- however, we can compress gas to fit more gas molecules into an already full gas container -- for example, the volume of helium used to fill helium balloons is more than the volume of the helium tank Why is this? -- volume is just the amount of space that matter takes up, therefore, putting more gas molecules in the same space isn’t increasing volume. Volume of gases is measured in mL or cm3

Temperature of a Gas Temperature is a measure of the average energy of motion of all of the particles in a substance -- when objects are at a high temperature, the molecules are moving faster -- gas molecules still move very fast no matter what the temperature of the substance is We measure temperature with a thermometer The units for temperature are either degrees Celsius (centigrade, °C) or Kelvin (K) K = °C + 273.15 The Kelvin scale is the Celsius scale, with absolute zero as the lowest point!

Pressure of a Gas Pressure is a measure of force Gas molecules in a container bounce off of one another and off of the walls of the container -- the more molecules, the more collisions, therefore, the more molecules, the greater the pressure We can calculate pressure using the following formula Force F Area A Pressure is measured in the units of kilopascals (kPa) Gases always flow from areas of high pressure to areas of low pressure -- this is why soccer balls deflate Pressure = or P =

Relationship Between T, V, and P All three properties of a gas are related: For example, if a gas is heated, the particles should move faster and spread further out, therefore increasing the volume of the container -- this is why some containers explode if heated – also how some bombs work -- but if the volume of the container increases, there will be less collisions with the walls, so pressure should decrease The actual relationship between temperature, pressure, and volume can be explained through the gas laws

Boyle’s Law Statement of Boyle’s Law: When held at a constant temperature, the volume of a gas varies inversely with the pressure of the gas In other words: -- While at a constant temperature, as volume of a gas increases, the pressure of a gas decreases -- While at a constant temperature, as volume of a gas decreases, the pressure of a gas increases

Mathematical Equation of Boyle’s Law Boyle’s Law is represented by the following equation: P1 x V1 = P2 x V2 Where: P1 is the initial pressure of the gas V1 is the initial volume of the gas P2 is the new pressure of the gas V2 is the new volume of the gas

Charles’s Law Statement of Charles’s Law: For a gas held at constant pressure, the temperature of the gas varies directly with the volume of the gas In other words: -- When the pressure of a gas is held constant, as the temperature of the gas increases, so does the volume of the gas -- When the pressure of a gas is held constant, as the temperature of the gas decreases, so does the volume of the gas

Mathematical Equation of Charles’s Law Charles’s Law is represented by the following equation: T1 T2 V1 V2 Where: T1 is the initial temperature of the gas V1 is the initial volume of the gas T2 is the new temperature of the gas V2 is the new volume of the gas =

Gas Laws Practice Problems At a temperature of 25°C, oxygen gas has a pressure of 85 kPa and a volume of 40 mL. What would the pressure of the oxygen gas be if the volume of the gas were changed to 50 mL? 2. What would the force exerted by the above gas be if it were trapped in a balloon with an area of 3 m2?

More Practice Problems 3. A gas is held at a constant pressure of 101.4 kPa. If the gas has an initial volume of 50 mL at a temperature of 20°C, what would the new temperature of the gas be if the volume of the container were increased to 75 mL?