q2w.key - Dr. Zellmer Time: 20 mins Name 1. KEY Chemistry...

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Dr. Zellmer Chemistry 122 Wednesday 9:30 AM Time: 20 mins Summer Quarter 2008 July 2, 2008 Quiz II Name KEY Rec. Instr. 1. (6 pts) At what temperature would CO molecules have a rate of effusion equal to that of CH 4 molecules at 40.0°C. (Mol. Wts.: CO = 28.01, CH 4 = 16.04) 3RT R = 8.314 J/mol C K T MUST be in kelvin : = (-------) 1/2 = molecular wt (molar mass in kg/mol if you want to calc : ) 3RT CO 3RT CH4 : CO = (----------) 1/2 : CH4 = (----------) 1/2 r eff % : (same applies to r diff ) CO CH4 r CO : CO CH4 T CO ------- = -------- = (--------------) 1/2 = 1 since : CO = : CH4 then r CO = r CH4 r CH4 : CH4 CO T CH4 This ratio given above for the rms speeds of 2 different molecules is general expression for this ratio in terms of the molar masses (molecular wts) and temperatures of the gases. It will not always be equal to 1, as it is in this case (because the speeds are the same). CH4 T CO ˆ ------------ = 1 CO T CH4 CO 28.01 g/mol T CO = (-------) T CH4 = (-----------------) 313. 1 5 K = 546. 8 4 K = 273. 6 9°C = 273.7°C CH4 16.04 g/mol (4 s.f.) 2. (5 pts) Write the staright-line form of the Clausius-Clapeyron equation. Explain what is plotted on the x and y axes and how you obtain ) H from the plot. P = Vapor Pressure ) H v = Heat (Enthalpy) of vaporization R = gas constant (8.314 J/mol C K T = temperature in kelvin This is an equation for a straight line, y = m * x + b, when you plot ln(P) versus 1/T.
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This note was uploaded on 07/17/2008 for the course CHEM 122 taught by Professor Zellmer during the Summer '07 term at Ohio State.

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q2w.key - Dr. Zellmer Time: 20 mins Name 1. KEY Chemistry...

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