Chapter 12 The Behavior of Gases
If a gas is heated, as in a hot air balloon, then its volume will increase. A heater in the balloon's basket heats the air inside the balloon and blows hot air into the balloon. As the volume of gas increases, it fills the balloon. Soon the balloon is full of hot air. If the air continues to heat up, it expands and flows out of the hole in the bottom of the balloon.
Hence a balloon filled with hot air contains fewer air molecules than the same balloon inflated to the same size with cool air. A hot air balloon will therefore be less dense than a balloon filled with cool air as a consequence of the ideal gas law.
Chapter 12 The Behavior of Gases The Properties of Gases Factors Affecting Gas Pressure The Gas Laws Ideal Gases Gas Molecules: Mixtures and Movements
Chapter 12.1 The Properties of Gases Kinetic Theory Revisited Variables That Describe a Gas
Kinetic Theory Revisited What do you recall about the Kinetic Theory as it relates to gases from Chapter 10?
Assumptions of the Kinetic Theory as applies to Gases 1)A gas is composed of molecules or atoms that have insignificant volume and are spread very far apart. In between is empty space. No attractive or repulsive forces exist.
Assumptions of the Kinetic Theory as applies to Gases 2) The particles in a gas move rapidly in constant random motion. a)Travel in straight paths. b) Change direction only when they collide.
Assumptions of the Kinetic Theory as applies to Gases 3) All collisions are perfectly elastic. Kinetic energy is transferred. It is never lost.
Collision Theory ion.swfhttp:// ion.swf
Variables That Describe a Gas Pressure (P) – kilopascals Volume (V) – liters Temperature (T) – Kelvin's Number of moles (n)
Chapter 12.2 Factors Affecting Gas Pressure Amount of a Gas Volume Temperature
Amount of a Gas What happens when you pump up a bike tire?
Amount of a Gas Increase the amount of gas the pressure increases Why? More particles = More Collisions
Amount of a Gas Gas moves from higher pressure to lower pressure
Volume If you decrease the volume, pressure ? Increases If you increase the volume, pressure? Decreases
Temperature If you increase the temperature of a gas, the pressure? Increases If you decrease the temperature of a gas, the pressure? Decreases
Chapter 12.3 The Gas Laws Boyle’s Law Charles’s Law Gay-Lussac’s Law Combined Gas Law
Boyle’s Law (1662) Pressure – Volume Relationship Pressure increases, Volume decreases Boyle’s Law – for a gas with a given mass at a constant temperature, the volume of the gas varies inversely with the pressure P 1 x V 1 = P 2 x V 2
Charles’s Law (1787) Temperature – Volume Relationship Temperature increases, Volume increases Charles’s Law – for a gas with a fixed mass at a constant pressure, the volume of the gas varies directly with the temperature V 1 = V 2 T 1 T 2
Gay-Lussac’s Law (1802) Temperature – Pressure Relationship Temperature increases, Pressure increases Gay-Lussac’s Law – for a gas at a constant volume, the pressure of the gas varies directly with the temperature P 1 = P 2 T 1 T 2
Combined Gas Law Combines all three laws P 1 V 1 = P 2 V 2 T 1 T 2
Chapter 12.4 Ideal Gas Law Ideal Gas Law and Kinetic Theory
Ideal Gas Law P x V = n x R x T (PV=nRT) n = number of moles R = Ideal Gas Constant = 8.31 L kPa K mol
Ideal Gas Law You fill a rigid steel cylinder that has a volume of 20.0 L with nitrogen gas to a final pressure of 20,000 kPa at 28ºC. How many moles of nitrogen gas does the cylinder contain? P = 20,000 kPa V= 20.0 L n = ? R = 8.31 L kPa K mol T = 28ºC
Ideal Gas Law PV = nRT Change temperature to Kelvin 28ºC = 301K Solve for the unknown (20,000kPa)(20.0L) = n (8.31 L kPa) (301K) K mol 160 mol N 2(g) = n
Ideal Gas Law A deep underground cavern contains 2.24x10 6 L of methane gas at a pressure of 1.50x10 3 kPa and a temperature of 42ºC. How many kilograms of methane does this natural gas deposit contain? 2.05x10 4 kg CH 4
Ideal Gas Law and Kinetic Theory States gas has no volume This is not a true statement All gases have mass Most gases behave like ideal gases.