Chapter 5 -lecture 2

Chapter 5 -lecture 2 - General Chemistry I Fall 2007 Joann...

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Unformatted text preview: General Chemistry I Fall 2007 Joann S. Monko Chemistry 9th ed. Raymond Chang Clicker Question Suppose a He balloon launches with a temperature of 22.5 C, a volume of 4.19 x 103 L, and a pressure of 760 mm Hg. At a higher elevation, the pressure is 744 mm Hg and it is -33.0 C outside. What is the volume of the balloon? a. 3.34 x 103 L c. 3.48 x 103 L e. 5.28 x 103 L b. 3.34 x 104 L d. 3.48 x 104 L Avogadro's Hypothesis Equal volumes of gases (same T & P) have the same number of molecules. V = kn = n (RT/P) V n V and n are directly related. twice as many molecules The gases in this experiment are all measured at the same T and P. Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Avogadro's Law V = n x constant V1 = V2 n1 n2 Temperature & Pressure are Not changed. Chemistry, 8th ed. Chang Propane burns in air according to the equation C3H8 (g) + 5 O2 (g) 3 CO2 (g) + 4 H2O (l) *What volume of O2 is required to completely react with 3.70 L of propane? *What volume of CO2 is produced? V n "stoichiometry" 3.70 L C3H8 x 5 L O2 1 L C3H8 = 18.5 L O2 3.70 L C3H8 x 3 L CO2 1 L C3H8 = 11.1 L CO2 Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Clicker Question Ammonia burns in air to yield nitrogen monoxide and water. How many liters of nitrogen monoxide are obtained from 2.5 L of ammonia at constant temp. and pressure? Figure 5.6 Chemistry, 8th ed. Chang Chemistry, 8th ed. Chang Pressure is constant Lower Temp = Decrease Volume Higher Temp = Increase Volume Figure 5.6 Chemistry, 8th ed. Chang Volume is constant Lower Temp = Decrease Pressure Higher Temp = Increase Pressure Figure 5.6 Figure 5.6 Chemistry, 8th ed. Chang IDEAL GAS LAW P V = n R T Brings together gas properties. Can be derived from experiment and theory. P = atm V = L n = moles T = K R = 0.0821 L atm/mol K Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. How much N2 is req'd to fill a small room with a volume of 960 cubic feet (27,000 L) to P = 745 mm Hg at 25 oC? 1. Get all data into proper units V = 27,000 L T = 25 oC + 273 = 298 K P = 745 mm Hg (1 atm/760 mm Hg) = 0.98 atm 2. Now calc. n = PV / RT Using PV = nRT (0.98 atm)(2.7 x 104 L) n = (0.0821 L atm/K mol)(298 K) n = 1.1 x 103 mol (or 30.8 kg of gas) Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Clicker Question The balloon used by Charles in historic flight in 1783 was filled with about 1300. moles H2. If the temperature of the gas was 23.0 C and the pressure was 750. mm Hg what was the volume of the balloon? Record your answer in kiloliters (kL) and one decimal place. STP Standard Temperature & Pressure (STP) 0 C and 1 atm 1 mole of an ideal gas occupies 22.414 L PV = nRT R = PV = (1 atm)(22.414 L) nT (1 mol)(273.15 K) R = 0.082057 L atm/mol K Chemistry, 8th ed. Chang Gases and Stoichiometry 2 H2O2 (l) ---> 2 H2O (g) + O2 (g) Decompose 1.1 g of H2O2 in a flask with a volume of 2.50 L. *What is the pressure of O2 at 25 oC? *Of H2O? Bombardier beetle uses decomposition of hydrogen peroxide to defend itself. Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Gases and Stoichiometry 2 H2O2(liq) ---> 2 H2O(g) + O2(g) Decompose 1.1 g of H2O2 in a flask with a volume of 2.50 L. What is the pressure of O2 at 25 oC? Of H2O? Strategy: Calculate moles of H2O2 and then moles of O2 and H2O. Finally, calc. P from n, R, T, and V. 1 mol 1.1 g H2 O2 34.0 g 0.032 mol Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. 1 mol O2 0.032 mol H2O2 = 0.016 mol O2 2 mol H2 O 2 2 H2O2(liq) ---> 2 H2O(g) + O2(g) Decompose 1.1 g of H2O2 in a flask with a volume of 2.50 L. What is the pressure of O2 at 25 oC? Of H2O? P of O 2 = nRT/V (0.016 mol)(0.0821 L atm/K mol)(298 K) = 2.50 L P of O2 = 0.16 atm What is P of H2O? Could calculate as above. But recall Avogadro's hypothesis. There are 2 times as many moles of H2O as moles of O2. P is proportional to n. So... P of H2O is twice that of O2. P of H2O = 0.32 atm Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Alterations to PV = nRT Density (d) d = m = PM V RT m is the mass of the gas in grams M is the molar mass of the gas (g/mol) Molar Mass (M) M = dRT P d is the density of the gas (g/L) Chemistry, 8th ed. Chang Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. USING GAS DENSITY The density of air at 15 oC and 1.00 atm is 1.23 g/L. What is the molar mass of air? 1. Calc. moles of air. V = 1.00 L P = 1.00 atm T = 288 K n = PV/RT = 0.0423 mol 2. Calc. molar mass mass/mol = 1.23 g/0.0423 mol = 29.1 g/mol Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Clicker Question Calculate the density of CO2 at STP. Record your answer to 2 decimal places (g/L). Dalton's Law of Partial Pressures Figure 5.14 P1 P2 Ptotal = P1 + P2 Chemistry, 8th ed. Chang Volume & Temperature are NOT changed. Dalton's Law of Partial Pressures The P of a mixture of gases is the sum of the partial pressures of the different gases. Ptotal = PA + PB + PC +... Mole Fraction: XA = nA John Dalton 1766-1844 Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. . nA + nB + nC Pressure of one gas: PA = XA (Ptotal) Dalton's Law of Partial Pressures 2 H2O2 (l) ---> 2 H2O (g) + O2 (g) 0.32 atm 0.16 atm What is the total pressure in the flask? Ptotal in gas mixture = PA + PB +... Therefore, Ptotal = P(H2O) + P(O2) = 0.48 atm Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. A mixture of 40.0 g of oxygen and 40.0 g of helium has a total pressure of 0.900 atm. What is the partial pressure of oxygen? 1. Convert grams to moles: 40.0 g O2 = 1.25 mol 40.0 g He = 10.0 mol 2. Find the mole fraction of O2: XO2 = 1.25 mol = 0.112 (1.25 + 10.0) mol X O2 = nO2 . nO2 + nHe 3. Partial pressure of O2: PO2 = XO2(Ptotal) = (0.112)(0.900 atm) =0.101 atm Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. 4. Partial pressure of He: PHe = Ptotal PO2 (0.900 0.101) atm = 0.799 atm He Clicker Question A sample of natural gas has a pressure of 1.37 atm and contains: 8.240 mol methane 0.421 mol ethane 0.116 mol propane What is the partial pressure of propane? (record answer to 4 decimal places) PTotal Collection Apparatus 2 KClO3 (s) 2 KCl (s) + 3 O2 (g) = PO + PH O = atmospheric pressure 2 2 Chemistry, 8th ed. Chang Pressure of Water Vapor Figure 5.16 Chemistry, 8th ed. Chang ...
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This note was uploaded on 04/08/2008 for the course CHEM 100 taught by Professor Monko during the Winter '08 term at Kutztown.

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