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9-4-08[lecture2]ht

# 9-4-08[lecture2]ht - Chem 116[Lecture 2 Class Notes[HT...

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Chem 116 [Lecture 2, 9/4/08] Class Notes [HT] Ideal Gas Law ( pV = nRT) In the example with the balloons at STP (Standard Temperature Pressure), the n is the number of moles [m(ass)/mw (molecular weight)] and is determined by using the ideal gas law. Example: How many moles ( n ) of He are in the 2.0L He balloon at STP? Solve: What information is given and what is being asked? STP assumes temperature (T) = 298 K, and pressure (p) = 1.00 atm. Volume (V) = 2.00 L, and (R) is a constant 0.080206 L·atm/mol·K. pV = nRT n = pV/RT n = (1.0 atm)(2.0L)/(0.080206 L·atm/mol·K)(298K) n = 0.0817866 mol n = 0.0818 mol He (3 sig figs) or 8.18 x 10 -2 mol He All four balloons have the same number of moles under the same constant conditions (temp., pressure, volume) under the Ideal gas law. They felt different due to the difference in molecular weight of each gas element. He (4g/mol) < N 2 (28g/mol) < CO 2 (44g/mol) < SF 6 (146g/mol) Particle Density In a closed system, as pressure is increased, density also increases. So pressure is proportional to

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