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AP Chemistry Unit 2. Chapter 5: Pressure; Boyle’s, Charles’, Avogadro’s laws; Ideal gas law; gas stoichiometry; Dalton’s law of partial pressures; KMT of gases; Effusion and diffusion; real gases. CB p. 2. A gas. Uniformly fills any container. Mixes completely with any other gas

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## AP Chemistry Unit 2

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**AP ChemistryUnit 2**Chapter 5: Pressure; Boyle’s, Charles’, Avogadro’s laws; Ideal gas law; gas stoichiometry; Dalton’s law of partial pressures; KMT of gases; Effusion and diffusion; real gases.**CB p. 2**A gas • Uniformly fills any container. • Mixes completely with any other gas • Exerts pressure on its surroundings.**CB p. 2**Pressure • is equal to force/unit area • SI units = Newton/meter2 = 1 Pascal (Pa) • 1 standard atmosphere = 1 atm • 1 atm = 760 mm Hg • 1 atm = 760 torr • 1 atm = 101.325 kPa**CB p. 2**Figure 5.1a: The pressure exerted by the gases in the atmosphere can be demonstrated by boiling water in a large metal can (a) and then turning off the heat and sealing the can.**CB p. 2**Figure 5.01b: As the can cools, the water vapor condenses, lowering the gas pressure inside the can. This causes the can to crumple (b).**CB p. 2**Figure 5.2: A torricellian barometer. The tube, completely filled with mercury, is inverted in a dish of mercury.**CB p. 2**Figure 5.3: A simple manometer.**CB p. 4**Boyle’s law* • Pressure Volume = Constant (T = constant) P1V1 = P2V2 (T = constant) V 1/P (T = constant) *Holds precisely only at very low pressures.**CB p. 4**A gas that strictly obeysBoyle’s Law is called an ideal gas.**CB p. 4**Boyle’s law**CB p. 4**Figure 5.4: A J-tube similar to the one used by Boyle.**CB p. 4**Figure 5.5: Plotting Boyle's data from Table 5.1. (a) A plot of P versus V shows that the volume doubles as the pressure is halved. (b) A plot of V versus 1/P gives a straight line. The slope of this line equals the value of the constant k.**CB p. 4**Figure 5.6: A plot of PV versus P for several gases at pressures below 1 atm.**CB p. 4**As pressure increases, the volume of SO2 decreases.**CB p. 4**Figure 5.7: A plot of PV versus P for 1 mol of ammonia. The dashed line shows the extrapolation of the data to zero pressure to give the "ideal" value of PV of 22.41 L • atm.**CB p. 6**Charles’ law The volume of a gas is directly proportional to temperature, and extrapolates to zero at zero Kelvin. V = bT (P = constant) b = a proportionality constant**CB p. 6**Figure 5.8: Plots of V versus T (ºC) for several gases.**CB p. 6**Figure 5.9a. 5.8 except here the Kelvin scale is used for temperature.**CB p. 8**Avogadro’s law For a gas at constant temperature and pressure, the volume is directly proportional to the number of moles of gas (at low pressures). V = an a = proportionality constant V = volume of the gas n = number of moles of gas**CB p. 8**Figure 5.10: These balloons each hold 1.0L of gas at 25ºC and 1 atm. Each balloon contains 0.041 mol of gas, or 2.5 x 1022 molecules.**CB p. 10**Ideal gas law • An equation of statefor a gas. • “state” is the condition of the gas at a given time. PV = nRT**CB p. 10**Ideal gas law PV = nRT R = proportionality constant = 0.08206 L atm mol P = pressure in atm V = volume in liters n = moles T = temperature in Kelvins Holds closely at P < 1 atm**CB p. 10**Standard Temperature and Pressure “STP” P = 1 atmosphere T = C The molar volume of an ideal gas is 22.42 liters at STP**CB p. 10**Figure 5.11: 22.4 L of a gas would just fit into this box.**CB p. 12**Dalton’s law of partial pressures For a mixture of gases in a container, PTotal = P1 + P2 + P3 + . . .**CB p. 12**Figure 5.12: The partial pressure of each gas in a mixture of gases in a container depends on the number of moles of that gas.**CB p. 12**Figure 5.13: The production of oxygen by thermal decomposition of KCIO3. The MnO2 is mixed with the KClO3 to make the reaction faster.**CB p. 16**Kinetic Molecular Theory (KMT) of gases 1. Volume of individual particles is zero. 2. Collisions of particles with container walls cause pressure exerted by gas. 3. Particles exert no forces on each other. 4. Average kinetic energy Kelvin temperature of a gas.**CB p. 16**The meaning of temperature Kelvin temperature is an index of the random motions of gas particles (higher T means greater motion.)**CB p. 16**Figure 5.21: A plot of the relative number of N2 molecules that have a given velocity at three temperatures.**CB p. 18**Root-mean-square-velocity • The symbol means the average of the squares of the particle velocities. • The square root of is called the root mean square velocity and is symbolized by u rms.**Diffusion: describes the mixing of gases. The rate of**diffusion is the rate of gas mixing. Effusion: describes the passage of gas into an evacuated chamber. CB p. 20 Diffusion vs. Effusion**CB p. 20**Figure 5.22: The effusion of a gas into an evacuated chamber.**CB p. 20**Figure 5.23: Relative molecular speed distribution of H2 and UF6.**CB p. 20**Figure 5.24: (top) When HCl(g) and NH3(g) meet in the tube, a white ring of NH4Cl(s) forms. (bottom) A demonstration of the relative diffusion rates of NH3 and HCl molecules through air.**CB p. 22**Real gases • Must correct ideal gas behavior when at high pressure(smaller volume) and low temperature(attractive forces become important).**CB p. 22**Real gases corrected pressure corrected volume Pideal Videal

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