14+Gas+Laws

=Objectives= 14.1 14.2 14.3 14.4
 * Why are gases easier to compress than solids or liquids are? 14 Gas LawsWhat are the three factors affect gas pressure?
 * How are the pressure, volume, and temperature of a gas related?
 * When is the combined gas law used to solve problems?
 * What is needed to calculate the amount of gas in a sample at given conditions of volume, temperature, and pressure?
 * Under what conditions are real gases most likely to differ from ideal gases?
 * How is the total pressure of a mixture of gases related to the partial pressures of the component gases?
 * How does the molar mass of a gas affect the rate at which the gas effuses or diffuses?

=Outlined Notes= 14.1 A.Properties of Gases 1.Compressibilty a.Compressibilty- measure of how much the volume of matter decreases under pressure. b.Gases are easily compressed because of the space between the particles. B.Factors Affecting Gas Pressure 1. The amount of gas, volume, and temperature are factors that affect gas pressure 2.Amount of Gas a.The kinetic theory can be used to predict and explain how gases will respond to a change of conditions. b. If the pressure of the gas in a sealed container is lower than the outside pressure, air will rush into the container when it is opened. 3.Volume a.The pressure exerted by a gas can be raised by reducing the volume. 4.Temperature a.As a gas is heated, the temperature increases and the average kinetic energy of the particles in the gas increases. b. When the Kelvin temperature of an enclosed gas doubles the pressure of the enclosed gas doubles

14.2 The Gas Laws A. Boyle's Law: Pressure and Volume a. If the temperature is constant, as the pressure of a gas increases, the volume decreases.

Robert Boyle, 1627-1691 b. Boyle's law- states that for a given mass of gas at constant temperature, the volume of the gas varies inversely with pressure.

B. Charles's Law: Temperature and Volume a. As the temperature of an enclosed gas increases, the volume increases, if the pressure is constant. b. Charles's law- states that the volume of a fixed mass of gas is directly proportional to its Kelvin temperature if the pressure is kept constant. C. Gay- Lussac's Law: Pressure and Temperature a. As the temperature of an enclosed gas increases, the pressure increases, if the volume is constant. D. The Combined Gas Law a. combined gas law- describes the relationship among the pressure, temperature and volume of an enclosed gas. b. The combined gas law allows you to do calculations for situations in which only the amount of gas is constant 14.3 Ideal Gases A. Ideal Gas Law 1. To calculate the number of moles of a contained gas requires an expression that contains the variable //n.// 2. Ideal Gas content- (r) has the value 8.31 (LxkPa)/(Kxmol) 3. Ideal Gas Law- The gas law that includes all four variables- P,V,T and n. P x V = n x R x T or PV= nRT B. Ideal Gases and Real Gases 1. Real gases differ most from an ideal gas at low temperature and high pressures.

14.4 A. Gases: Mixtures and Movements 1. Dalton's Law a.Partial pressure- the contribution each gas in a mixture makes the total pressure b. In a mixture of gases, the total pressure is the sum of the partial pressures of the gases. c. Dalton's law of partial pressures- at constant volume and temperature, the total pressure exerted by a mixture of gases is equal to the sum of the partial pressures of the component gases. 2. Graham's Law a. Diffusion- the tendency of molecules to move toward areas of concentration until the concentration is uniform throughout. b. Effusion- a process that involves the movement of molecules in a gas c. Gases of lower molar massdiffuse and effuse faster than gases of higher molar mass. d. Thomas Graham's law of effusion- the rate of effusion of a gas is proportional to the square root of the gas's molar mass. e. Comparing Effusion Rates

Example
Let gas 1 be H2 and gas 2 be O2. Therefore, hydrogen molecules effuse four times as fast as those of oxygen. Graham's Law can also be used to find the approximate molecular weight of a gas if one gas is a known species, and if there is a specific ratio between the rates of two gases (such as in the previous example). The equation can be solved for either one of the molecular weights provided the subscripts are consistent.

=Reference Pages=



[]
 * Pressure is inversely proportional to the volume:**
 * ~ Units of Pressure ||
 * 1 pascal (Pa) || 1 N*m-2 = 1 kg*m-1*s-2 ||
 * 1 atmosphere (atm) || 1.01325*105 Pa ||
 * 1 atmosphere (atm) || 760 torr ||
 * 1 bar || 105 Pa ||

= = = = =Practice Problems= 1. A sample of carbon dioxide occupies a volume of 1.2 liters at 720 torr pressure. What volume will it occupy at 50 torr pressure? __1.2 x 720__ = 17.28 liters 50 2. A 250. mL container of hydrogen gas had a pressure of 740 torr. What volume would be nessasary to decrease the pressure to 25 torr? __250 x 740__ = 7400 mL 25 1. A sample of hydrogen gas occupies a volume of 250 mL at 25 C. What volume will it occupy at 67 C? 25 + 273 = 298 K 67 + 273 = 340 K __250 x 340__ = 285 mL 298 2. Argon gas was cooled from 75 C to 50 C. Its new volume is 75 mL. What was its original volume? 75 + 273 = 348 K 50 + 273 = 323 K __348 x 75__ = 80.8 mL 323 1. A gas at 240 kPa and 303 K has an initial volume of 40 L. The pressure stays constant while the volume becomes 125 L. What is the new temperature? Since pressure is constant, it will cancel out and you do not need to include it in the equation. __303 x 125__ = 947 K 40 [] []
 * Boyle's Law**
 * Charles's Law**
 * Combined Gas Law**

1.) 2.00 g of hydrogen gas and 19.2 g of oxygen gas are placed in a 100.0 L container. These gases react to form H2)O(g). The temperature is 38 degrees celsius at the end of the reaction. a. What is the pressure at the conclusion of the reaction? b. If the temperature was raised to 77 degrees celsius, what would the new pressure be in the same container? []
 * Ideal Gas Law**

2.) 1 mole of oxygen gas and 2 moles of ammonia are placed in a container and allowed to react at 850 degrees celsius according to the equation: 4NH3(g) + 52(g) -->4NO(g) + 6H2O(g)
 * Pressure Problem**

a. If the total pressure in the container is 5.00 atm, what are the partial pressures for the three gases remaining? b. Using Graham's Law, what is the ratio of the effusion rates of NH3(g) to O2(g)? []

=Assignments= media type="custom" key="3544720"

=Labs= [] [|http://chem.gmu.edu/results/as%20Laws%20(211).doc] [] [] [] [] [] []l [] []
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=Sample Test= [] [] [] [] []
 * [] needs downloaded**

= = =**Links [] Gas Law Information [] [|http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch4/gaslaws3.html][] [] [|http://www.chm.davidson.edu/chemistryapplets/gaslaws/GasConstant.html http://www.shodor.org/UNChem/advanced/gas/][] [] [] [] [] [] [] []**= =http://en.wikipedia.org/wiki/Gas_law= [] [|www.iun.edu/.../ gases/charleslaw.html] [] [|http://chemistry.about.com/cs/workedproblems/a/bl113003a.htmhttp://chemistry.about.com/cs/workedproblems/a/bl011804.htm]