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HONORS CHEMISTRY May 6, 2014 Brain Teaser • Rationalize the following observations. – A thin-walled can will collapse when the air inside is removed by a vacuum pump. – Aerosol cans will explode if heated Agenda • Brain Teaser • Notes: Combined Gas law, Avogadro’s Law and Ideal Gas Law • Homework – Combined Gas Law Worksheet • Questions 2,4,6,8 – Ideal Gas Law Worksheet • Questions 1,2,4,6 Combined Gas Law Boyle’s Law Charles’s Combined P1V1 P2V2 V1 V2 T1 T2 P1V1 P2V2 T1 T2 Avogadro’s Law • How can we change the volume of a gas in a balloon? Avogadro’s Law • Why did the blimp deflate? Avogadro’s Law • If the pressure and temperature are held constant, the V volume m(n)of ba gas is directly proportional to the number of moles (n). b0 V m n V1 V2 n1 n2 V n Gas Laws Part 2: Work on Gas Notes Sheet instead of Brain Teaser Avogadro’s Law O2 O 3 Suppose we have a 12.2 L sample containing 0.50 mol oxygen gas at a pressure of 1 atm and a temperature of 25 ºC. 1) Balance the equation 2) If all this oxygen is converted to ozone at the same temperature and pressure, what would be the volume of the ozone? • The total pressure is the sum of the partial pressures. • Ptotal = P1 + P2 + P3 + ….. Dalton’s Law Practice • A mixture of oxygen, carbon dioxide, and nitrogen has a total pressure of 0.97atm. What is the partial pressure of Oxygen, if the partial pressure of carbon dioxide is 0.70atm and the partial pressure of nitrogen is 0.12atm? The Gas Laws • Variables: V, P, T, n (or m and MM or d) • Ideal Gas: properties are independent of the identity of the gas • What is the relationship between the variables for an ideal gas? Basketball Bike Tire 5.3 Ideal Gas Law • • • • • PV = nRT P= pressure (atm) V = volume (L) n = number of moles R = ideal gas constant – 0.08206 L·atm/mol·K • T = temperature (K) STP • Standard Temperature and Pressure – 0ºC and 1 atm • Use the Ideal Gas Law to calculate the volume of 1.00 mol of gas at STP Molar Volume at STP • We can show that 22.414 L of any gas at 0C and 1 atm contain 6.02 1023 gas molecules. Example • A sample of Hydrogen gas has a volume of 8.56 L at 0ºC and a pressure of 1.5 atm. Calculate the moles H2 molecules present in this gas sample. Practice Problem • The volume of an oxygen cylinder is 1.85 L. What mass of oxygen gas remains in the cylinder when it is “empty” if the pressure is 755 torr and the temperature is 18.1oC? • Answer: 2.46 g