CHAPTER 5 GASES 5 1 PRESSURE Properties Gases

CHAPTER 5 - GASES

5. 1 PRESSURE � Properties � Gases of Gases uniformly fill any container � Gases are easily compressed � Gases mix completely with any other gas � Gases exert pressure on their surroundings

5. 1 PRESSURE � Measuring � The barometric pressure barometer � Invented by Evangelista Torricelli in 1643 � Units � mm Hg (torr) � newtons/m 2 (pascal (Pa)) � Atmospheres 760 torr = 1 atm 101, 325 Pa = 101. 3 k. Pa 1 atm = standard pressure

5. 2 THE GAS LAWS OF BOYLE, CHARLES AND AVOGADRO Boyle’s law (Robert Boyle) The product of pressure times volume is a constant, provided the temperature and number of moles remains the same � Pressure and volume are inversely related � Volume increases linearly as the pressure decreases (1/P)

5. 2 THE GAS LAWS OF BOYLE, CHARLES AND AVOGADRO Boyle’s Law Continued…… � At constant temperature, Boyle’s Law can be used to fine a new volume or pressure Boyle’s law works best at low pressures � Gases that obey Boyle’s Law are called Ideal Gases �

5. 2 THE GAS LAWS OF BOYLE, CHARLES AND AVOGADRO Charles’ Law (Jacques Charles) The volume of a gas increases linearly with temperature provided the pressure and number of moles remain constant. � Temperature proportional and volume are directly

5. 2 THE GAS LAWS OF BOYLE, CHARLES AND AVOGADRO Charles’ Law continued………. . � Temperature must be measured in degrees Kelvin �K = o. C + 273. 15 � 0 K is “absolute zero”

5. 2 THE GAS LAWS OF BOYLE, CHARLES AND AVOGADRO Avogadro’s Law (Amedeo Avogadro) For a gas at constant temperature and pressure, the volume is directly proportional to the number of moles.

5. 3 THE COMBINED GAS LAW Combined gas law – (n remaining constant)

5. 3 THE IDEAL GAS LAW � Derived from existing laws……. �V = k/P, V = b. T and V = an � V = (k)(b)(a)(Tn/P) � Constants k, b and a are combined into the universal gas constant R and…. .

5. 3 THE IDEAL GAS LAW � Limitations � Works of the Ideal Gas Law well at low pressure and high temperatures � Most gases do not behave ideally above 1 atm � Does not work well near the condensation conditions of a gas

5. 3 THE IDEAL GAS LAW Variations of the Ideal Gas Law Density Molar Mass of a gas

5. 4 GAS STOICHIOMETRY At Standard Temperature and Pressure (STP) T = 273. 15 K (0 o. C) P = 1 atm (760 torr or 101. 3 k. Pa) 1 mole of an ideal gas occupies 22. 4 L of volume Remember……. . Density = mass/volume and