Gases Chapter 11

Kinetic Theory and Gas Properties The kinetic theory assumes that –Volume of gas particles is insignificant –There is space between gas particles –Gas particles do not attract or repel each other –Gas particles move rapidly and in constant random motion

Variables that Describe a Gas Pressure (atm, mmHg, kPa) Volume (L) Temperature ( ˚ C or K ) Number of moles (mol)

What happens if you… decrease the volume of the container? –Pressure may increase –Temperature may increase increase the temperature? –Pressure may increase –Volume may increase Increase the pressure? –Temperature may increase –Volume may decrease

Gas Laws Boyles P 1 x V 1 = P 2 x V 2 Charles V 1 = V 2 T 1 T 2 Gay-Lussac P 1 = P 2 T 1 T 2

How do we tie it all together? P 1 V 1 = P 2 V 2 T 1 T 2 AKA: The Combined Gas Law Allows you to predict what will happen to a gas if some of the conditions change!

Lets Practice! A gas with a volume of 4.0L at 90.0kPa expands until the pressure drops to 20.0kPa. What is the new volume if the temperature remains constant? Identify what you know V 1 =4.0L P 1 =90.0kPa P 2 =20.0kPa T 1 =T 2 Solve for what you don’t know V 2 = P 1 V 1 x T 2 T 1 P 2 V 2 = 18L

Now you try! A gas with a volume of 3.00x10 2 mL at ˚ C is heated until its volume is 6.00x10 2 mL.What is the new temperature of the gas if the pressure remains constant at 1.0 atm during the heating. T 2 = T 1 x P 2 V 2 P 1 V 1 T 2 = 300 ˚ C

Ideal Gases vs. Real Gases Particles have no volume Particles are not attracted or repelled to each other Ideal gases can never be liquefied or solidified Particles have volume Particles experience intermolecular forces Real gases can be liquefied and solidified

Real Gases Act Like Ideal Gases When temperatures are very high and pressures are very low Can you explain why? –High Temperatures means lots of kinetic energy so particles are moving rapidly and randomly –Low Pressures means particles do not hit the container (and each other) often, so they cannot feel attraction and repulsion

The Ideal Gas Law Allows us to solve for a property of an ideal gas when properties are constant! PV=nRT P=pressure V=volume T=temperature n=number of moles R= 8.31 L x kPa or L x atm K x mol K x mol

Let’s Practice Determine the volume occupied by mol of a gas at 15 ˚ C if the pressure is 81.1 kPa. Identify what you know n=0.582 mol T=15 ˚ C = 288 K P=81.1 kPa. R= 8.31 L x kPa / K x mol V=17 L

When to use the equations If the conditions of the gas change Then use the combined gas law If the conditions of the gas are fixed Then use the ideal gas law