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UNIT 7Gas LawsKEY IDEASConceptWhat does it mean?Exampleideal gasKelvinideal gas lawgas constantpressurepartial pressurestandard pressurevolume’s relationship with pressuretemperature’s relationship with pressuretemperature’s relationship with volume7.0 – What is pressure? Pressure is force exerted per areaforce is exerted by particles as they hit the walls of their containermore particles = _____________________________ = _____________________________High PressureLow PressureThe many units to measure pressurestandard atmospheric (atm): based on the average atmospheric pressure at sea levelPascals (Pa): Newtons per metre squaredtorr (Torr) or millimeters of mercury (mmHg): pressure applied by 1 mm of mercuryBar (bar): the atmospheric pressure at sea levelPounds per square inch (psi)PRESSUIRE CONVERSION TABLEatmkPaTorrmmHgbarpsi1 atm =1101.325760.760.1.0132514.71 kPa =0.0098717.507.500.01000.1451 Torr =0.001320.133110.001330.01931 bar =0.987100.750.750.114.51 mmHg =0.001320.133110.001330.01931 psi =0.06806.8951.751.70.06891Example: Convert the following.What is 120 kPa in mmHg?What is 952 Torr in atm?7.1 – What is temperature? Temperature is the __________________________________________ of particlesHigh temperature = high KE = more collision with container = high pressureHigh temperature = container expansion = increase in volumeTemperature scalesThe Celsius scale defines 0 as the point at which _____________________, and 100 the point at which _________________________The Kelvin scale defines 0 as _____________________________, the temperature at which ______________________________________________The size of one unit of degree Celsius is the _______________ as one unit of degree KelvinDegrees in Kelvin = ______________________ Example: Convert the following.What is 25°C in Kelvin?What is 0 K in °C?What is -32°C in Kelvin?7.2 – Ideal Gas Law To study gases and to come up with some equations to describe the behaviour of gases, scientists made a few assumptionsGases are composed of _____________________________ particlesThese particles _________________________________ (they take up no space!)Gas particles do not interact with each other except when they collideCollisions are perfectly elastic (KE before collision = KE after)When these assumptions are made, the behaviour of gasses can be summed up with the Ideal Gas Law.SymbolStands forUnit Practice:What is the volume of a 12.0 g sample of methane gas at 25°C and 755 mmHg of pressure?A flashbulb of volume 2.6 mL contains O2 gas at a pressure of 2.3 atm and a temperature of 26°C. How many moles of O2 does the flashbulb contain?What is the density of CO2 at 745 mmHg and 65°C?What volume is occupied by 1.00 mol of gas at 0°C and 1.00 atm? What do you notice?7.3 – Boyle’s Law Where did the ideal gas law come from? It was created from the work of multiple Scientists.Robert Boyle: In a closed system, the pressure of a gas is inversely proportional to its volume if temperature and mass is constant.High volume, low pressureLow volume, high pressureMathematically Speaking…As V increases, P decreasesIn other words, if we change the volume of a substance in the same room, keeping the amount of that substance the same, we can derive a neat little formula. Before After The number of moles of a gas does not change when it is being compressedIf before and after occur in the same room, and we don’t disturb the gas, T1 = T2 (and obviously the two R’s are the same)ThereforeExample:A mass of gas occupies 1.25 L at a pressure of 101.3 kPa. The pressure is changed to produce a volume of 0.59 L. What is the new pressure?A 10.0 g sample of a gas occupies a volume of 8.0 L at STP. What volume does this gas occupy at standard temperature and 300 kPa?7.4 – Charles’s Law Jacques Charles: In a closed system under constant pressure, the volume of an ideal gas is proportional to its absolute temperature.High temperature, high volumeLow temperature, low volumeMathematically Speaking…As T increases, V increasesIn other words, if we change the temperature of a substance in the same room, keeping the amount of that substance the same, we can derive a neat little formula. Before After If V and T are related in some way, we could say thatIf volume and temperature is always related in the same way, thenExample:If a sample of gas measures 2.00 L at 25°C, what is its volume at 50°C if the pressure remains constant?If a sample of gas measures 500. cm3 at STP, what is its volume of 101.3 kPa and 34°C?7.5 – Combined Gas Law If we put the ideas from Boyle and Charles together, we get the combined gas law, which relates pressure, temperature, and volume.Assuming we have a constant amount of gasSo if we have a before and after situation where we examine a system of gas that experiences a change in pressure, volume, or temperatureExample:A gas has a volume of 4.7 L at a temperature of 57°C and a pressure of 100. mmHg. What would its volume be at STP?If you breathe 3.0 L of helium at 20°C and 101.3 kPa, you will talk funny. You think that would be fun. You breathe all the helium in a container at 15°C and 110.6 kPa and you aren’t talking funny. Why not?7.6 – Partial Pressures The total pressure of a system containing a mixture of gases is the sum of the pressures exerted by each gas.158115013779516573501778000Example:A gaseous mixture made from 6.00 g O2 and 9.00 g CH4 is placed in a 15.0 L vessel at 0°C. What is the partial pressure of each gas (O2 = 0.280 atm, CH4 = 0.560 atm)What is the total pressure of the vessel in atm? (0.840 atm)What is the total pressure, in atm, exerted by a mixture of 2.00 g H2 and 8.00 g N2 at 273 K in a 10.0 L vessel? (2.9 atm)Example:If 1 mol of O2 has a pressure of 1 atm, then 0.5 mol of O2 should exert a pressure of ____________.If 1 mol of S has a pressure of 1 atm, then 0.5 mol of S should exert a pressure of ____________.If 0.5 mol of O2 is mixed with 0.5 mol of S, the mixture should exert a pressure of ____________, assuming that O2 does not react with S.A glass bulb contains a mixture of 0.0150 moles of He(g), and 0.0350 moles of Ar(g). If the pressure in the bulb is 60.0 kPa, what is the partial pressure of each gas?7.7 – Stoichiometry with Gas Laws Example: Chlorine can be made in the laboratory from the given reaction. What volume of Cl2 can be produced from 5.00 g of HCl in the lab which is at 25.0 oC and 101 kPa?4HCl + MnO2 MnCl2 + Cl2 + H2OExample: What mass of water is produced with 500.0 mL of acetylene, C2H2, at 760. mmHg and 110°C is burned in excess oxygen?Example: Suppose the 25.0 L air bag in your car is designed to contain 1.25 atm of pressure when deployed at 25 °C. What mass of sodium azide (NaN3) will be required to decompose into Na(s) and N2(g)? ................
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