Chem 105a Week 6 notes
Chem 105a Week 6 notes CHEM 105A
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This 3 page Class Notes was uploaded by Emma Morrissey on Friday September 30, 2016. The Class Notes belongs to CHEM 105A at University of Southern California taught by Thomas Michael Bertolini in Fall 2016. Since its upload, it has received 10 views. For similar materials see General Chemistry in Chemistry at University of Southern California.
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Date Created: 09/30/16
9/26/16 Chapter 5 Continued ● STP and Molar Volume ○ STP- standard temperature and pressure oC ■ 0 and 1 atm ○ Molar volume- the volume of one mole of gas at stp is 22.42 L ■ Note that real gases have slightly different volumes, but we are only considering ideal gases ● Molar mass of a gas ○ Molar mass and density can be calculated from PV=nRT ○ n = molar masslar mass =mPVRT density =V ● Partial Pressures ○ For a mixture of gases in a container, the total pressure exerted is the sum of the pressures that each gas would exert if it were alone ○ The total pressure is the sum of the pressures due to each gas ○ Ptotal=P1+P2+P3+... ○ For an ideal gas mixture, the total pressure depends on the total number of moles, not the identity or amount of each component ○ The mole fraction is the ratio of the moles of a given gas in a mixture to the total moles in the mixture n P ■ x =n10 = P1 total total ● Collecting a gas over water ○ When a gas is collected by displacement of water, it always contains a small amount of water vapor ○ The vapor pressure of water must be subtracted from the total pressure 9/28/16 ● Kinetic Molecular Theory ○ Kinetic Energy ■ Gas particles frequently collide and exchange kinetic energy ■ A sample of gas at a given temperature has particles with a wide range of velocities ● Temperature is the average kinetic energy ■ At higher Temperatures, these ranges become very broad ● Temperature and kinetic energy ○ Temp is a measure of average KE 3 ○ KE avg 2T ○ R has units of J mo* K ● Root mean square velocity 3RT J ○ μrms=√ MM MM= molar mass kg per mol; R= 8.3145 mol K ● Effusion and Diffusion ○ Effusion- movement of a gas through a pinhole into an evacuated chamber ■ Graham’s Law of Effusion ● At the same temp and pressure, the relative rates of effusion of two gases are given by: Effusion rate fo√ 2as 1 ○ Effusion rate fo√MG1s 2 ○ Lower molar mass; lighter gas particles; higher velocity; faster gas ○ Diffusion- the mixture of gases ■ Think of a perfume spreading through a room ● Real vs Ideal Gases ○ Ideal gas particles ■ Are volumeless ■ Strike each other with elastic collisions ■ Have no attraction to each other ○ Real gases behave like ideal gases at ■ Low Pressure: the particles’ volumes are less significant because they are much smaller in comparison to the volume of the container ■ High Temperature: high KE makes collisions more elastic ● Van Der Waals Equation ○ The van der Waals equation is a modification of the ideal gas law that closely fits real gas behavior n 2 ○ [P +a(V) ] * (V −nb) = nRT ○ The bracketed quantity is an adjustment to correct for the pressure caused by intermolecular forces ○ The quantity in parentheses is a correction of volume ○ “A” accounts for interactions among gas particles ■ Gases with weak intermolecular forces have low a values ○ “B” subtracts the volume of gas molecules themselves ■ Generally increases with the size of the gas molecule 9/30/16 ● Continued ○ These constants are experimentally determined ○ No need to memorize constants nor van der Waals equation Chapter 6 (Skip section 10) ● Thermochemistry- the relationship between matter and energy ● Energy- capacity to do work ● Work- force acting over a distance ● Potential Energy- energy stored due to position or composition ● Kinetic Energy- energy due to motion of an object ● System- any defined environment ● Surroundings- everything else ● System + Surroundings = Universe ● Units of energy ○ Joule (J)- the energy needed to move 1 kg mass 1 m using a force of 1 Newton ■ 1 J = 1 Nm ○ Calorie (cal)- the energy needed to raise 1 g of water by one degree celsius ■ 4184 J ■ Kcal- food calories- energy needed to raise 1 kg water ○ Kilowatt-hour (kWh)- used to measure electrical energy ■ 3.60 E 6 J ● First Law of Thermodynamics ○ The total energy of the universe is constant. Or, energy is neither created nor destroyed ■ Energy can be transferred between objects ■ Energy can be transformed from one form to another