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CHEMISTRY

CHEMISTRY. IT’S A GAS!! Chapter 13. Units of Pressure. 1atm = 101.3 kPa = 760 torr = 760 mm Hg = 14.7 psi Measured with a barometer or manometer to measure pressure less than atmospheric. Assumptions About Properties of Gases – Kinetic Theory p.475-477.

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CHEMISTRY

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  1. CHEMISTRY IT’S A GAS!! Chapter 13

  2. Units of Pressure • 1atm = 101.3 kPa = 760 torr = 760 mm Hg = 14.7 psi • Measured with a barometer • or manometer to measure pressure less than atmospheric

  3. Assumptions About Properties of Gases – Kinetic Theory p.475-477 • Small particles with lots of space between-insignificant volume • Compressible • High kinetic energy – random motion and straight paths • Elastic collisions • No attractive or repulsive forces between particles

  4. Variables That Describe Gases • Pressure (P) – kPa, atm, Torr, mm Hg, psi, bars or mbars • Volume (V)– liters • Temperature (T)– Kelvin scale • Moles (n) – number of moles

  5. Gas Laws • Allow us to predict behavior of gases under specific conditions. • Help us understand everyday applications of gases • Why do we have to check air pressure in tires? • Why did my balloon shrink in the cold? • Why does warm soda fizz so much?

  6. Factors Affecting Gas Pressure • Amount of gas – number of particles/moles • Volume – space gas takes up • Temperature – increases or decreases kinetic energy of particles resulting in more or fewer collisions

  7. Boyle’s Law p.447 • Describes pressure-volume relationship of gases at constant temperature • States that for a given mass of gas, as pressure increases, volume decreases and vice versa • What kind of relationship is this? • How can it be expressed mathematically? • P1V1 = P2V2

  8. Charles’ Law p.451 • Describes the relationship between volume and temperature at constant pressure. • States that for a fixed mass of gas, as temperature increases, volume increases and vice versa • What kind of relationship is this? • How can this be expressed mathematically? • V1/T1 = V2/T2

  9. Gay-Lussac’s Law • Describes relationship between temperature and pressure with constant volume • States that the pressure of a gas will increase with increased temperature and vice versa • What kind of relationship is this? • How can it be expressed mathematically? • P1/T1 = P2/T2

  10. Combined Gas Law p. 464 • Combines Boyle’s, Charles’ and Gay-Lussac • Allows for calculations where none of the variables is constant • P1V1/T1 = P2V2/T2

  11. Ideal Gas Law p.458 • Incorporates the fourth variable of gases – number of moles • When “n” is included in combined gas law a constant is recognized and symbolized as “R” with value of 8.31L.kPa/K.mol • “R” is known as the ideal gas constant • New mathematical expression PV=nRT

  12. Ideal Gas p.458 • One that follows all gas laws at all conditions of pressure and temperature • No such gas – however, real gases behave as ideal gases under most conditions of pressure and temperature • Real gases can be liquefied and sometimes solidified – ideal gases cannot

  13. Real vs Ideal p.478 • Kinetic theory assumptions – no attraction among particles and no volume • Assumptions are incorrect! • If true, would not be able to liquefy or solidify gases • Gases definitely have volume

  14. Avogadro’s Hypothesis p.455 • Equal volumes of gases at the same temperature and pressure contain equal numbers of particles • One mole (6.02 x 1023 particles) of any gas at STP occupies a volume of 22.4 L • This works because gas particles (even large ones) are so small and there is so much space between them.

  15. Dalton’s Law of Partial Pressuresp. 464 • States at constant volume and temperature the total pressure exerted by a mixture of gases is equal to the sum of the partial pressures • Expressed mathematically P1 + P2 + P3…= Ptotal

  16. Graham’s Law • Describes diffusion and effusion of gas molecules • States that rate of effusion is inversely proportional to the square root of the gases’ molar mass • Also found to be true for diffusion of gases • Simply put, means small gas molecules move faster than heavier gas molecules

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