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Chapter 5 - Chapter 5 Gases Matter exists in three distinct...

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Chapter 5 Gases Matter exists in three distinct physical states, gas, liquid and solid Under normal conditions relatively few substances exist in the gaseous state The atmosphere is a mixture of gases consists mainly of element nitrogen (N 2 ) and oxygen (O 2 ) The industrial waste of gases leads to many types of pollution such as smog and acid rains Gases in the atmosphere shield us from harmful radiation from the sun and keep the earth warm 5.1 Pressure : A gas uniformly fills any container and exerts pressure on its surroundings Barometer is a device to measure the atmospheric pressure Monometer is a device to measure gas pressure ( See Figures 5.2 and 5.3 ) Units of pressure : 1 standard atmosphere = 1 atm = 760 mmHg = 760 torr = 101325 Pa = 101.325 KPa

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5.2 Gas Laws : 1) Boyle 2) Charles 3) Avogadro Boyle’s Law : Pressure α 1/Volume P α 1/ V PV = constant Example 5.2 : For sulfur dioxide SO 2 : P 1 = 5.6 x 10 3 Pa V 1 = 1.53 L P 2 = 1.5 x 10 4 Pa V 2 = ? Answer : PV = constant P 1 V 1 = P 2 V 2 V 2 = P 1 V 1 / P 2 = (5.6 x 103 Pa)/(1.5 x 104 Pa) x 1.53 L = 0.57 L 2
Charles’s Law : Volume α Temperature V α T V / T = constant where, T is temperature in Kelvin Example 5.4 : A sample of gas at 1 atm has: V 1 = 2.5 L T 1 = 15 o C V 2 = ? T 2 = 38 o C Answer : V / T = constant V 1 / T 1 = V 2 / T 2 V 2 = V 1 T 2 / T 1 = (2.58 L x 311 K)/(288 K) = 2.79 L 3

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Avogadro’s Law : Volume α number of moles V α n V / n = constant Example 5.5 : For a sample of O 2 gas at 1 atm and 25 o C: V 1 = 12.2 L n 1 = 0.50 mol If all O 2 were converted to ozone O 3 at the same temperature and pressure, what would be the volume of ozone ( V 2 )? Answer : 3O 2 (g) 2O 3 (g) 3 mol of O 2 = 2 mol of O 3 0.50 mol of O 2 = (?) n 2 of O 3 n 2 = (0.50 mol x 2 mol)/(3 mol) = 0.33 mol of O 3 V / n = constant V 1 / n 1 = V 2 / n 2 V 2 = ( V 1 / n 1 )( n 2 ) = (12.2 L / 0.50 mol) x (0.33 mol) = 8.1 L 4
5.3 The Ideal Gas Law : Boyle’s Law: V α 1/ P Charles’s Law: V α T Avogadro’s Law: V α n Combining the three laws gives the ideal gas law: V α nT / P V = RnT / P PV = nRT ( ideal gas law) where, R is called universal gas constant and R = 8.314 J mol -1 K -1 = 0.08206 atm L mol -1 K -1 Remember : PV = constant V / T = constant PV / T = constant 5

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Example 5.9 : For a sample of diborane gas (B 2 H 6 ): P 1 = 345 torr t 1 = -15 o C (258 K) V 1 = 3.48 L P 2 = 468 torr t 2 = 36 o C (309 K) V 2 = ? Answer
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Chapter 5 - Chapter 5 Gases Matter exists in three distinct...

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