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GASES (chapter 10)

GASES (chapter 10). By Dieu Ngo. Characteristics of Gases. Essential for life Expand to fill container Compressible Readily flow Form homogeneous mixtures with other gases Vol of gases itself=smaller portion of total volume at room temp. and pressure Noble gases= monotomic gases

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GASES (chapter 10)

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  1. GASES (chapter 10) By Dieu Ngo

  2. Characteristics of Gases • Essential for life • Expand to fill container • Compressible • Readily flow • Form homogeneous mixtures with other gases • Vol of gases itself=smaller portion of total volume at room temp. and pressure • Noble gases=monotomic gases • Diatomic gases • Gases: molecular compounds, nonmetals • Vapors

  3. Properties of Gases • T- temperature (in K) • V- volume (in L) • n- quantity (in moles) • P- pressure (in atm)

  4. Gas Pressure • P=F/A • Barometer-contains a column of mercury (Hg) whose height is directly related to the pressure exerted by the atmosphere (mm Hg or torr) • Manometer- used to measure pressure in enclosed gases (usually below atm. Pressure); det’ed from the difference in heights of mercury levels in U-tube

  5. Atmospheric Pressure • Caused by gravity • Atoms of atm.=tiny massesoverride gravitational forces • Magnitude: F= ma • a = 9.8 m/s^2

  6. Standard Atmospheric Pressure • PRESSURE= 1 atm = 760 mmHg = 760 torr = 1.013E5Pa = 101.3kPa • Pgas= Patm+Ph

  7. Gas Laws • Boyle’s Law- V=contant/P (T, n) ;or P1V1=P2V2 • Charles Law- V= constant x T (P, n); or V1/T1=V2/T2 • Gay-Lussac’s Law- V= constant x n (P, T); or P1/T1=P2/T2

  8. Ideal-Gas Equation • PV=nRT • P in atm • V in L • n in moles • T in K • R is gas constant = 0.0821 L-atm/mol-K • Combined: PV/T=PV/T

  9. Standard temp. and pressure • STP: • Pressure = 1 atm • Temperature = 0 degrees Celsius = 273K • Volume of 1 mol= 22.4 L

  10. Dalton’s Law of Partial Pressure • The total pressure of a mixture of ideal gases is the sum of the individual pressures each ideal gas would exert if it were the only gas in the container • Pt=P1+P2+…+PN • Pi=niRT/V • Pt=Pgas+PH2O

  11. Mole Fraction (X) • The ratio of the # of moles of a component in a mixture of the total # of moles present • Xi = #of moles of component i / total # of moles in mixture • PA = (XA)(PT) • Vol % of a gas in a mixture = mole fraction of that gas

  12. Kinetic Molecular Theoryof Gases • KMT- at the same temperature, molecules of all gases have the same average translational kinetic energy • rms speed is the square root of the average of the squared velocities of the gas molecules: • The average speed is the average of the velocities: • Temp increases  speed increases • The rms speed of a gas is inversely related to the molar mass of the gas at a given temp:

  13. Effusion • Is the flow of gas molecules through a small pinhole or small opening into a vacuum • Graham’s Law of Effusion relates the rates of 2 gases escaping through the same pinhole and their molar masses at constant temperature

  14. Lalalalalalala… chemistry! • Diffusion- A process in which a substance gradually mixes with another • Mean Free Path- the average distance gas molecules travel between collisions

  15. Gas molecules vs. ideal gas • Gas molecules- attracts at short distances  do not collide with walls of container like ideal gas • Cause the experimental gas pressure to be less than the ideal-gas pressure • Vol for gas to move in container < total vol of container • Van der Waals equation:

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