Chapter 9 Gases: Their Properties and Behavior CHEMISTRY

S TOICHIOMETRIC R ELATIONSHIPS WITH G ASES Methanol (CH 3 OH) can be synthesized by the following reaction: CO(g) + 2 H 2 (g) -- > CH 3 OH(g) What volume (in Liters) of hydrogen gas, measured at a temperature of 355K and a pressure of 738 mmHg, is required to synthesize 35.7 g of methanol?

E XAMPLES Determine the mass of NaN 3 required for an air bag to produce 100.0L of N 2 gas at 85.0 o C and 1.00 atm according to the equation 2 NaN 3 (s) -- > 2Na(s) + 3N 2 (g)

P ARTIAL P RESSURE AND D ALTON ’ S L AW P total = P 1 + P 2 + … + P N Mole Fraction (X) = Dalton’s Law of Partial Pressures: The total pressure exerted by a mixture of gases in a container at constant V and T is equal to the sum of the pressures of each individual gas in the container. X i = P total PiPi X i = n total nini or Total moles in mixture Moles of component

E XAMPLES A 1.00 L vessel contains moles of N 2 gas and moles of H 2 gas at 25.5 o C. Determine moles fraction of each gas Determine the partial pressure of each gas Determine the total pressure

E XAMPLES Determine the number of moles of each gas present in a mixture of CH 4 and C 2 H 6 in a 2.00L vessel at 25.0 o C and 1.50 atm, given that the partial pressure of CH 4 is 0.39 atm

T HE K INETIC -M OLECULAR T HEORY OF G ASES 1.A gas consists of tiny particles, either atoms or molecules, moving about at random. 2.The volume of the particles themselves is negligible compared with the total volume of the gas; most of the volume of a gas is empty space. 3.The gas particles act independently of one another; there are no attractive or repulsive forces between particles. 4.Collisions of the gas particles, either with other particles or with the walls of a container, are elastic (constant temperature). 5.The average kinetic energy of the gas particles is proportional to the Kelvin temperature of the sample.

T HE K INETIC -M OLECULAR T HEORY OF G ASES average speed molar mass

T HE K INETIC -M OLECULAR T HEORY OF G ASES

G RAHAM ’ S L AW : D IFFUSION AND E FFUSION OF G ASES Diffusion: The mixing of different gases by molecular motion with frequent molecular collisions.

G RAHAM ’ S L AW : D IFFUSION AND E FFUSION OF G ASES Graham’s Law: Effusion: The escape of a gas through a pinhole into a vacuum without molecular collisions.  Rate 1 m

G RAHAM ’ S L AW : D IFFUSION AND E FFUSION OF G ASES In comparing two gases at the same temperature and pressure √m2 √m1 Rate 1 Rate 2 =

E XAMPLE Determine how much faster Helium atoms moves, on average, than a carbon dioxide molecule at the same temperature Determine the molar mass and identity of a gas that moves 4.67 times as fast as CO 2

T HE B EHAVIOR OF R EAL G ASES The volume of a real gas is larger than predicted by the ideal gas law.

T HE B EHAVIOR OF R EAL G ASES Attractive forces between particles become more important at higher pressures.