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# Gases Pt.1

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### Gases Pt.1

1. 1. Pressure<br />Pressure is force per unit area<br />In the English system, pounds per square inch or psi<br />Atmospheric pressure is about 14.7 psi<br />Pressure = Force<br />Area<br />1 atm = 14.7 psi<br />1 atm = 760 mmHg<br />The mmHg is also called the Torr after Torricelli, inventor of the barometer<br />SI unit of measurement, the pascal (Pa)<br />1 Pa is the pressure exerted by a 0.1 mm high film of water on the surface beneath it<br />The bar = 105 Pa<br />1.013 bar = 1 atm = 760 mmHg = 14.7 psi = 100 kPa<br />
2. 2. Gas Pressure Measurement<br />The barometer measures pressure in terms of the height of a column on liquid mercury<br />The atmosphere exerts a force on a pool of mercury, causing it to rise<br />One standard atmosphere of pressure is a column of mercury 760 mm high<br />Mercury is used to keep the column a manageable height <br />
3. 3. Gas Pressure Measurement cont.<br />The manometer measures gas pressure by differential<br />The height of the column of liquid is proportional to the pressure<br />Gas pressure can be more or less than atmospheric pressure<br />
4. 4. Dalton’s Law of Partial Pressure<br />Dalton’s law of partial pressures states that the sum of the partial pressures of gases sum to the total pressure of the gases when combined.<br />Ptot = P1 + P2 + P3 + …<br />
5. 5. Boyles’s Law<br />The product of the pressure and volume for a trapped sample of gas = a constant (k)<br />PV = k <br />P1V1= P2V2 for analysis of a system before and after<br />
6. 6. Sample Boyle’s Law problem<br />A quantity of gas under a pressure of 106.6 kPa has a volume of 380 dm3. What is the volume of the gas at 103.3 kPa, if the temperature is held constant?<br />P1 x V1 = P2 x V2<br />(106.6 kPa) x (380 dm3) = (103.3 kPa) x (V2)<br />V2 = 400 dm3<br />
7. 7. Absolute Zero and the Kelvin Scale<br />Absolute Zero is the temperature where all motion stops (-273C)<br />For gases, the SI unit uses the Kelvin (K) scale. <br />Kelvins = (273 + C)<br />
8. 8. Charles’ Law<br />The volume of each gas is directly proportional to temperature<br />V = bT<br />B = a constant<br />V1/T1 = V2/T2<br />Temperature is in Kelvins (273 + C)<br />
9. 9. Charles’ Law Calculation<br />At constant pressure, the volume of a gas is increased from 150 dm3 to 300 dm3 by heating it. If the original temperature of the gas was 20 oC, what will its final temperature be (oC)?<br />T1 = 20 oC + 273 = 293 K<br />T2 = X K<br />V1 = 150 dm3<br />V2 = 300 dm3<br />
10. 10. Avogadro’s Law<br />Volume is directly proportional to the number of moles of gas<br />V = an<br />V1/n1 = V2/n2<br />
11. 11. The Combined Gas Law<br />
12. 12. Sample Problem<br />A sample of helium gas has a volume of 0.180 L, a pressure of 0.800 atm and a temperature of 29°C. What is the new temperature(°C) of the gas at a volume of 90.0 mL and a pressure of 3.20 atm?<br />