Essential question: How do chemists describe gases? Gas Laws Essential question: How do chemists describe gases?

Properties of a Gas Particles in a gas are spread apart There is no attraction between the gas particles Gases have no definite volume Gases fill the container that they are in and take that shape Contrast this with what you know about solids and liquids

Kinetic Theory of Gases Temperature Temperature is a measure of the average kinetic energy of the particles (KE is the energy of motion) The hotter a substance becomes the faster the particles move

Kinetic Theory of Gases Gas particles are constantly moving Particles bounce off each other and the walls of a container Pressure is related to the amount the particles bounce off the sides of the container

There are 3 components of Gases Pressure Temperature Volume

Atmospheric Pressure Atmospheric Pressure: pressure exerted by Earth’s atmosphere; measured by a barometer Standard atmospheric pressure: column of mercury is 760 mm high at 0oC at sea level 6

Pressure Pressure can be measured in Converting Atmospheres, atm mm Hg (Torr; another name for mm Hg) Pascal Pa – kilopascal kPa Converting 1 atm = 760 mm Hg = 101.35 kPa Know how to convert between all three units of pressure

Temperature For gas laws temperature is measured in the Kelvin scale, K Conversion K = C + 273 Kelvin is an absolute temperature scale At 0 K there is no movement of particles

Standard Pressure and Temperature Standard pressure and temperature for a gas is 1 atm and 0ºC or 273°K You will be expected to remember this

Volume Volume is measured in liters Avogadro determined that for any gas at STP will occupy 22.4 liters of space and contain 6.02 x 1023 molecules or atoms

Human Gas Particle Activity You will act as gas particles You will Walk in straight lines When you bump into another “gas particle you will turn and walk in a new direction You will not Walk with purpose at another gas particle Hold on to another gas particle

Human Gas Particle Activity You, as a gas particle, will base you rate of walking based upon temperature What happens to the rate of movement when temperature changes I will use a metronome to indicate temperature Failure to follow the rules will lead to removal from the gas container

What happens if we keep T constant If we lower the pressure volume increases If we take a balloon up a mountain it will increase because of the lower pressure If we increase the pressure volume decreases As we squeeze a balloon it shrinks This is an inverse relationship

Boyle’s Law When temperature is constant, there is an inverse relationship between pressure and volume P1V1 = P2V2 Remember, “Boyle at a constant temperature

What happens if we keep Pressure constant? If pressure is constant If temperature goes up then volume goes up What happens to a balloon in the sun? If temperature goes down volume goes down What happens to a balloon in the winter? This is a direct relationship

Charles Law Under constant pressure, there is a direct relationship between volume and temperature V1/T1 = V2/T2 Remember, Charles works under constant pressure

What happens we keep Volume constant and change the other two If we keep volume constant The pressure will go up if temperature increases Faster particles will bang against the container more The pressure will go down if temperature goes down Slower particles bounce against the container less This is a direct relationship

The Third Law Also named for Gay-Lussac Under constant volume, there is a direct relationship between temperature and pressure P1/T1 = P2/T2

What happens when more than one variable changes There are 3 variables to gases Temperature Pressure Volume If more than one variable changes can you predict the third? The 3 laws can be combined

The Combined Gas Law Boyle’s Charle’s Law The Third Law P1V1 = P2V2 Charle’s Law V1/T1 = V2/T2 The Third Law P1/T1 = P2/T2 Combined they form P1V1/T1 = P2V2/T2 Can you see all three laws in this one formula?