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

• http://www.kscience.co.uk/animations/collision.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 12.3The 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

• P1 x V1 = P2 x V2

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

• V1 = V2

T1 T2

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

• P1 = P2

T1 T2

Combined Gas Law

• Combines all three laws

• P1 V1 = P2 V2

T1 T2

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 + 273 = 301K

• Solve for the unknown

• (20,000kPa)(20.0L) = n (8.31 L kPa) (301K)

K mol

• 160 mol N2(g) = n

Ideal Gas Law

• A deep underground cavern contains 2.24x106 L of methane gas at a pressure of 1.50x103 kPa and a temperature of 42ºC. How many kilograms of methane does this natural gas deposit contain?

• 2.05x104 kg CH4

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.