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GASES Chapter 5 Gas 1. Least dense of the forms of matter Solid is more dense than liquid; liquid is more dense than gas 2. Properties A. Diffusion - move-a-bility of gas Gasoline or ether can be smelled rapidly. Gas fumes move. B. Pressure - push-a-bility The volume of a gas expands with heat and contracts with cold. T8 V8 T9 V9 If pressure is applied to a gas, the volume will decrease. P8 V9 P9 T8
Gases How many molecules in 1 mole of H2 gas? How many atoms in 1 mole of H2 gas? How many molecules in 1 mole of methane gas (CH4)? How much does 1 mole of H2 gas weigh? How much does 1 mole of CH4 gas weigh? Review A. 1 mole of every gas will contain Avagadro's number of molecules 6.02 x 1023. B. The weight of 1 mole of gas will vary according to the molecular weight of the gas. Volumes of Gases p 121 At standard temperature and pressure, 1 mole of gas will occupy 22.4 liters. Standard temperature is 00 C and standard pressure is 1 atmosphere. Formula 1 mole of gas @ STP = moles @ STP What is the volume of 2 moles of O2 at STP? What is the volume of 2 moles of CH4 at STP? How much does 2 moles of O2 weigh? How much does 2 moles of CH4 weigh?
ATMOSPHERIC PRESSURE p 115 Measure in mm Hg (mercury) 760 mm Hg at sea level. The air pushes on the Hg and makes it rise to the 760 mm mark.
Denver has .8 atmospheric pressure. How many mm Hg would that be equivalent to? 760 mm Hg = 760 Torr = 105 Pascals = 1 atm
GAS LAW FORMULAS P1V1 =
P2V2
PV =
nRT Effect of Pressure on Gas Volume The more pressure the smaller the volume - squeeze-a-bility of a gas Boyle's Law BP At constant temperature the volume of a gas is inversely proportional to pressure. Drill 1. At 1 atm pressure the volume of a gas is 1 liter. What would be the volume at 2 atm pressure? Pressure inversely proportional to volume more pressure, less volume Pƒ V„ P„ Vƒ Visualize a balloon under pressure. It gets smaller. P1 = 1 atm
P1V1 = P2V2 2. 1.5 liters of gas is under pressure of 2.5 atm. If the pressure is decreased to 0.75 atm, what is the new volume?
4. A gas holds 2000 liters at 820 mm pressure. If the temperature remains constant, what will the volume of gas be at standard pressure?
Effect of Temperature on Gas Volume Principle - the higher the temperature the more volume needs. Charles Law - at constant pressure, the volume of a given quanity of gas varies directly with absolute temperature. How to do Problems Think in terms of K Definition of Kelvin scale is the coldest it can get. There is no -5K. All molecular activity stops at 0K. 1. 1.50 liters of gas at 25oC is heated to 350oC. The pressure remains the same. What is the new volume? a. The greater the heat the greater the volume. T1 = 25oC = 273 + 25 = 298K T2 = 350oC = 273 + 350 = 623K 2. The volume of a gas at 210oC is 2.6 liters. What is the volume at -10oC if the pressure remains constant? T1 = 210oC = ______K 3. Ammonia gas at 50oC occupies 20 liters. What is its volume at 0oC pressure remaining constant?
4. What is the new volume when 1.4 liters of gas at 0.80 atm pressure and 20oC is changed to 1.5 atm pressure at 110oC?
Drill
2. A sample of gas occupies 1000 ml at 760 mm pressure. If the temperature remains constant, what would be the volume of the gas (a) at 100 mm pressure (b) at 500 mm pressure and (c) at 2.5 atm pressure?
3. The volume of a sample of oxygen is 5.0 liters at 722 mm and 20oC. What volume will the oxygen occupy at standard pressure and 20oC?
4. A mass of neon occupies 200 ml at 100oC. Find its volume at 0oC, the pressure remaining constant.
Gay-Lussac p 117 The pressure of a gas at a given volume is directly proportional to its temperature (K) with the volume remaining constant. Have an airtight can - heat it. What happens?
A can of air at 27E C and sea level is closed tightly. It is heated to 327E C. The volume is constant. What is the pressure on the inside of the can in Torr?
Recap Boyle's Law Volume is inversely proportional to the pressure Charles' Law Volume is directly proportional to the temperature Gay-Lussac's Law Pressure is directly proportional to Temperature
Combination of the three laws
A sample of O2 gas occupies a volume of 1.62 L at 755 mm Hg pressure and at a temperature of OE C. What volume will this gas sample occupy at 725 mm Hg pressure and 50E C?
STP means standard temperature and pressure. Volume of a Mole of Gas 1. What is the weight of 22.4 liters of O2 at STP?
2. What is the weight of 44.8 liters of O2 at STP?
Problem: How many moles of oxygen gas are present in 2 liters at 2 atm pressure and 27EC? We could find out what the volume would be at STP ( 1Atm, 0EC) and then do a ratio. P1 = 2 atm
P1V1 = P2V2
If you were given the volume of a gas at a particular temperature and pressure, you could find the volume at STP. Then you could find the number of moles of that gas using the 22.4 L = 1 mole. There is another formula which is shorter. PV = n
R T P = pressure in Atm (if given in Torr change to Atm) How many moles of oxygen gas are present in 2 liters at 2 atm pressure and 27EC? (Would the answer be different for hydrogen gas?)
How many grams of oxygen are present in the example above? b) How many grams of hydrogen would you have?
How many grams of CO2 gas are there in a one liter container at 27E degrees C and 608 Torr?
A sample of C2H2 gas has a volume of 5.00 L at a pressure of 1.00 atm and a temperature of 100E C. What will be the temperature of the gas, in degrees Celsius, if the volume is decreased to 1.00 L and the pressure is increased to 5.00 atm?
An adult human breathes in approximately 0.500 L of air at 36E C and 1.00 atm pressure with every breath. What would this "breath volume" be at the same pressure if the temperature drops to 24E C?
DALTON=S LAW OF PARTIAL PRESSURES p 123 In a mixture of gases each gas acts independently from the other gases. Dalton=s Law of partial pressures states that the total pressure of a mixture of gases is the sume of the individual pressures. Pressure Total = Pressure of gas 1 + Pressure of gas 2 + Pressure of gas 3 To a tank already containing N2 at 2.0 atm pressure and O2 at 1.0 atm, we add an unknown quantity of CO2 until the pressure is 4.6 atm. What is the partial pressure of the CO2?
BREATHING p 124 A gas flows from an area of higher pressure to an area of lower pressure. The air we breathe is approximately 21% oxygen at a partial pressure of 159 mm Hg. The air in the alveoli is about 100 mm Hg. Oxygen flows into the lungs. The CO2 pressure in the lungs is 40 mm Hg and the CO2 pressure in the air is only 0.3 mm Hg. The CO2 flows out of the lungs.
Breathing and Boyle=s Law p 119 When the diaphram is contracted, it moves down giving less pressure on the lungs and air is inhaled. When the diaphram is relaxed, it is longer and moves up giving less area in the rib cage. The pressure on the lungs is greater and air is exhaled. Hyperbaric Medicine p 120 If tissues are starved for oxygen increasing the 21% oxygen to 100% will usually help. But if the problem is carbon monoxide poisoning, the CO holds on tenaciously to the hemoglobin and won=t allow the oxygen to replace the carbon monoxide. In order for the tissues to get oxygen, the oxygen is dissolved under high pressure 2 to 3 atm in the blood. The dissolved oxygen then goes to the tissues. The entire medical unit is under high pressure and the patient and the staff mus undergo gradual compression and at the end of the treatment undergo decompress;ion. Other uses: radiation necrosis, chronic refractory osteomyelitis (bone infection that does not heal), gaqs gangrene, smoke inhalation, cyanide poisoning, skin grafts, and thermal burns. Breathing pure oxygen for long periods destroys lung tissues.. O2 for 6 hrs Recommended exposure: 2 hrs at 2 atm and 90 min at 3 atm Problems at end of Chapter 5 - 5.14; 5.17; 5.18; 5.19; 5.23; 5.27; 5.29; 5.43 |
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Wednesday, March 21, 2007 01:28:01 PM |