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 The molecules that make up the gas are free to move about, and a gas will take up the size and shape of its container.

Pressure : P P = 1 atm=760mmHg=101.3 kPa Temperature : T T in Kelvin K = ºC Volume: V V in L 1 L = 1 dm 3 =1000 mL Moles: n n = m/MM STP=> standard temperature and pressure: 0°C and 1 atm

Why do my ears pop? As the number of molecules of air around you decreases, the air pressure decreases. This causes your ears to pop in order to balance the pressure between the outside and inside of your ear.

Scuba stands for "self-contained underwater breathing apparatus.“ I.At depth, pressure compresses the lungs. Divers take in more air as they descend, and their bodies absorb more nitrogen the deeper they go. II.One possible consequence is called nitrogen narcosis..

 As a diver descends beneath the surface the concentration of nitrogen in his body increases as a result of the high atmospheric pressure. The respiratory gases are compressed and larger amounts dissolve into the body tissues. Ascent after a deep dive must be done slowly as the dissolved gases are released as the external pressure decreases. A rapid decreases in atmospheric pressure leads to a case of the 'bends', or decompression sickness. The diver experiences feelings of dizziness, vomiting and joint pain, and in severe cases, temporary paralysis and other neurological symptoms. These symptoms occur because large bubbles of nitrogen gas block small veins and arteries cutting off oxygen supply. Treatment is with oxygen and prevention involves a very slow ascent to the surface for any deep dives.

 Gases consist of large numbers of molecules that are in random motion  The volume of all the molecules of the gas is negligible compared to the total volume in which the gas is contained  Attractive and repulsive forces between gas molecules is negligible  The average kinetic energy of the molecules does not change with time.  At any given temperature, the molecules of all gases have the same average kinetic energy.

Robert Boyle ( ) o Boyle was born into an aristocratic Irish family o Became interested in medicine and the new science of Galileo and studied chemistry. o A founder and an influential fellow of the Royal Society of London

Boyle’s Law P 1 V 1 = P 2 V 2 (T = constant) Pressure is inversely proportional to volume when temperature is held constant.

A Graph of Boyle’s Law

L of a gas is at 1.08 atm. What pressure is obtained when the volume is 10.0 L? L of a gas is at mmHg pressure. What is its volume at standard pressure?

Jaques Charles ( Jaques Charles ( )  French Physicist  Conducted the first scientific balloon flight in 1783

Charles’s Law The volume of a gas is directly proportional to temperature.

 Example #1: 4.40 L of a gas is collected at 50.0°C. What will be its volume upon cooling to 25.0°C?

Joseph Louis Gay-Lussac  French chemist and physicist  Known for his studies on the physical properties of gases.  In 1804 he made balloon ascensions to observe the composition and temperature of the air at different altitudes.

Gay Lussac’s Law The pressure and temperature of a gas are directly related, provided that the volume remains constant.

 1. If a gas is cooled from K to K and the volume is kept constant what final pressure would result if the original pressure was mm Hg  2. If a gas in a closed container is pressurized from 15.0 atmospheres to 16.0 atmospheres and its original temperature was 25.0 °C, what would the final temperature of the gas be?

The Combined Gas Law The combined gas law expresses the relationship between pressure, volume and temperature of a fixed amount of gas. Stp: 1 atm and 0 ˚C

 1. A 350 cm 3 sample of helium gas is collected at 22.0 o C and 99.3 kPa. What volume would this gas occupy at STP?

 An ideal gas is one, which obeys the general gas equation of PV = nRT and other gas laws at all temperatures and pressures.  A real gas, does not obey the general gas equation and other gas laws at all conditions of temperature and pressure.

n = m/MM d = m/V P x MM = d xR x T Values of R: R = if P is in atm R = 8.31 kPa if P is in kPa R = 62.4 mmHg if P is in mmHg

1. A sample of argon gas at STP occupies 56.2 liters. Determine the number of moles of argon g. of a gas occupies 48.0 L at mm Hg and 20.0 °C. What is its molecular mass?

1. A sample of argon gas at STP occupies 56.2 liters. Determine the number of moles of argon and the mass in the sample. 1 x 56.2 = n x x 273 n = 2.51 moles g. of a gas occupies 48.0 L at mm Hg and 20.0 °C. What is its molecular weight? 700 x 48 = n x 62.4 x 293 n = = 96/MM MM = 52 u 3. If grams of a gas are enclosed in a liter vessel at K and atmospheres of pressure, what is the molar mass of the gas? What gas is this? 4. What is the density of helium at room temperature and pressure?

 At STP, 1 mole of any gas occupies a volume of 22.4 L: n = V/22.4

1. Calculate the number of moles of ammonia gas, NH 3, in a volume of 80 L of the gas measured at STP.

n = 80 / 22.4 n = 3.57 moles

 What volume is occupied by 200g of CO 2 at stp ?

 n = V/22.4  n=m/MM  n=200/44 =  V = x 22.4 = 101.8L

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