Chapter 9 Gases: Their Properties and Behavior

Gases and Gas Pressure Gas mixtures are homogeneous and compressible.

Gases and Gas Pressure Pressure: Unit area Force

Pressure Imbalance in Ear 4 If there is a difference in pressure across the eardrum membrane, the membrane will be pushed out – what we commonly call a “popped eardrum.”

Gases and Gas Pressure Barometer Pa torr mm Hg atm bar Units

Gases and Gas Pressure (exact) Conversions 1 torr = 1 mm Hg 1 atm = Pa (exact)1 atm = 760 mm Hg (exact)1 bar = 1 x 10 5 Pa

Gases and Gas Pressure

The Gas Laws Ideal Gas: A gas whose behavior follows the gas laws exactly. The physical properties of a gas can be defined by four variables: Ppressure Ttemperature (calculation must be in Kelvin) Vvolume nnumber of moles

The Gas Laws Boyle’s Law  V P 1 (constant n and T)

The Gas Laws Boyle’s Law  V P 1 (constant n and T)

The Gas Laws P initial V initial = P final V final Boyle’s Law  V P 1 (constant n and T) PV = k

Boyle’s Law and Diving since water is denser than air, for each 10 m you dive below the surface, the pressure on your lungs increases 1 atm at 20 m the total pressure is 3 atm 12 if your tank contained air at 1 atm pressure you would not be able to inhale it into your lungs

Examples Calculate the volume of a sample of a gas at 5.75 atm if it occupies 5.14 L at 2.49 atm. (Assume constant temperature)

The Gas Laws Charles’ Law V  T (constant n and P) = k T V = T final V final T initial V initial

The Gas Laws Charles’s Law V  T (constant n and P)

The Gas Laws = k T V = T final V final T initial V initial Charles’s Law V  T (constant n and P)

Examples A sample of argon gas that originally occupied 14.6 L at 25.0 o C was heated to 50.0 o C at constant pressure. What is its new volume?

The Gas Laws Avogadro’s Law V  n (constant T and P) = k n V = n final V final n initial V initial

Examples Consider two samples of nitrogen gas (composed N 2 molecules). Sample 1 contains 1.5 mol of N 2 and has a volume of 36.7 L at 25.0 o C and 1.0 atm. Sample 2 has a volume of 16.0 L at 25.0 o C and 1.0 atm. Calculate the number moles of N 2 in sample 2

The Ideal Gas Law =Avogadro’s Law: P initial V initial = P final V final Boyle’s Law: n final V final n initial V initial Charles’ Law: = T final V final T initial V initial Summary If the systems is disturbed by one of the four variables: O, T, n then consider the following changes

Combine Gas Law is an expression obtained by mathematically combining Boyle’s and Charles’ law P 1 V 1 = P 2 V constant n T 1 T 2 can predict P, V or T when condition is changed

Examples Suppose we have a mol sample of ammonia gas at 25.0 o C with a volume of 3.5 L at a pressure of 1.68 atm. The gas compressed to a volume of 1.35 L at 25.0 o C. Use the combined gas law to calculate the final pressure.

The Ideal Gas Law PV = nRT Standard Temperature and Pressure (STP) for Gases Ideal Gas Law: P = 1 atm T = 0 °C ( K) R is the gas constant and is the same for all gases. R = K mol L atm

Examples What volume is occupied by 25.7 g of carbon dioxide gas at 25.0 o C and 371 torr? A mol sample of argon gas has a volume of 9.00L at a pressure of 875 mmHg. What is the temperature (in o C) of the gas? Determine the molar mass of a gas with a density of g/L at 80.0 o C

The Ideal Gas Law = LV = P nRT = What is the volume of 1 mol of gas at STP ? (1 atm) (1 mol) K mol L atm ( K)

The Ideal Gas Law

examples A sample of nitrogen gas has a volume of 1.75 L at STP. How many moles of N 2 are present? What is the volume of 12.5 g of an methane (CH 4 ) gas at STP