Lec18 Gases and it's properties - Chapter Outline 1....

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LMALaput Chemistry 16 Lecture 18 Chapter Outline 1. Properties of gases 2. Gas pressure and its measurement 3. The Gas laws 4. Ideal Gas Law 5. Solving Gas Law Problems GASES vs LIQUIDS vs SOLIDS •The density of gases is much less than that of solids or liquids. •Gas molecules must be very far apart compared to liquids and solids. •Liquids and gases are fluids. –They easily flow. PROPERTIES OF GASES 1. Gases can be compressed into smaller volumes. Their densities can be increase by applying increased pressure . 2. Gases exert pressure on their surroundings. In turn, pressure must be exerted to confine gases. 3. Gases can expand without limits. Gases completely and uniformly occupy the volume of any container. 4. Gases diffuse into one another, and so samples of gas placed in the same container mix completely . Conversely, different gases in a mixture do not separate on standing. 5. The amounts and properties of gases are described in terms of temperature, pressure, the volume occupied and the number of moles present. PRESSURE •is force per unit area. (lb/in 2 ,N/m 2 ) •Atmospheric pressure is measured using a barometer. •Definitions of standard pressure: –76 cm Hg –760 mm Hg –760 torr –1 atmosphere –101.3 kPa BOYLE’S LAW: P and V relationship •V 1/P or V= k (1/P) or PV = k P 1 V 1 = k 1 ; P 2 V 2 = k 2 ; k 1 = k 2 for the same sample of a gas at the same T; Thus we can write Boyle’s Law mathematically as P 1 V 1 = P 2 V 2 Example: At 25°C a sample of He has a volume of 4.00 x 10 2 mLunder a pressure of 7.60 x 10 2 torr. What volume would it occupy under a pressure of 2.00 atm at the same T? P 1 V 1 = P 2 V 2 V 2 = P 1 V 1 / P 2 = (760 torr)(400 mL) / 1520 torr = 2.00×10 2 mL CHARLES’S LAW: T and V relationship •Charles’s law states that the volume of a gas is directly proportional to the absolute temperature at constant pressure. – Gas laws must use the Kelvin scale to be correct. V T or V = kT or V/T = k V 1 / T 1 = k; V 2 / T 2 = k; V 1 / T 1 = V 2 / T 2 Example: A sample of hydrogen, H2, occupies 1.00 x 102mLat 25.0°C and 1.00 atm. What volume would it occupy at 50.0°C under the same pressure?
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This note was uploaded on 07/09/2011 for the course SCIENCE 16 taught by Professor Uperg during the Spring '11 term at University of the Philippines Diliman.

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Lec18 Gases and it's properties - Chapter Outline 1....

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