Week 9 notes
Week 9 notes CHEM 120
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This 2 page Class Notes was uploaded by Leslie Pike on Friday October 23, 2015. The Class Notes belongs to CHEM 120 at Western Kentucky University taught by Dr. Darwin Dahl in Summer 2015. Since its upload, it has received 41 views. For similar materials see College Chemistry I in Chemistry at Western Kentucky University.
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Date Created: 10/23/15
Chem 120 notes Week 9 Note the ideal gas law is PVnRT At normal temperatures and pressures ALL gases obey this law Gases deviate from this law at extremely high pressures and low temperatures Also this law no longer applies once a gas becomes a liquid We assume for all problems worked in class that a the gas does not deviate from this law and b the gas does not become a liquid Sample problem You have a 15 g impure sample of potassium chlorate You heat it and it decomposes into potassium chloride and oxygen You collect 30 mL of oxygen gas over water The temperature is 20 C The pressure is 730 mmHg Calculate the percentage of potassium chlorate in the sample Balanced reaction 2KCO3 D 2KC 302 First realize that this is a stoichiometry problem You need to nd the number of moles of oxygen gas that you collected so that you can nd the number of moles of potassium chlorate that you originally had Convert this to grams and divide by the grams of sample to get the percentage To nd the number of moles of oxygen use the ideal gas equation PVnRT Solving for n gives us nPVRT To determine the pressure of the oxygen remember that your container will have a combination of oxygen and water vapor because you collected over water use the law of partial pressures PtPoxygen Pwater Pwater can be found on the table that Dr Dahl will provide you with 730Poxygen 175 Poxygen7125 mmHg Now we can plug and chug Remember that pressure must be in atm volume must be in L and temperature must be in K 7125 xomo 11 00821 273 20 0001169 mol 02 The rest is stoichiometry 022m01 KCl 03 122g KClO3 3mol 02 000169 mol 0095g KCZO3 mol KCl 03 Lastly nd the mass percentage 00951563 Gas equations Equation for velocity of a gas v3RTM Here R8314 Mmoar mas in KILOGRAMS per mole NOT GRAMS Ttemperature in Kelvin Kinetic enerqv The kinetic energy equation is 05mv2 This equation itself is not important for Chem 120 From this is derived the equation used to compare the velocities of two gases 2 m2 V2 m1 The kinetic energy of a gas is directly proportional to its temperature KE1Z1 KE2T2 Therefore to get the relationship the kinetic energy of gas 1 and the kinetic energy of gas 2 divide the temperature of gas 1 by the temperature of gas 2 The rateofeffusion equation that compares two different gases is similar to the velocitymass relationship Rate 1 molar mass 2 Rate 2 molar mass 1 For example say it takes 2 liters of hydrogen gas molar mass 2 gmol 5 minutes to escape from a container How long would it take 3 liters of helium gas molar mass 4 gmol to escape from the same container The hydrogen escapes at a rate of 2L5min or 04Lmin The helium is three liters the number of minutes is unknown Filling in the equation 04Lmin3LX minsqrt4gmol2gmol Three liters of helium would take 106 minutes to escape the container
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