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Gas Laws Ch. 14

Gas Laws Ch. 14. Gases. Kinetic Molecular Theory (KMT) says: Gases have mass demo Gases are easily compressed Gases fill their container completely Gases move through each other easily (diffusion) Gases exert pressure (balloons, wind,atmosphere)

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Gas Laws Ch. 14

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  1. Gas Laws Ch. 14

  2. Gases • Kinetic Molecular Theory (KMT) says: • Gases have massdemo • Gases are easily compressed • Gases fill their container completely • Gases move through each other easily (diffusion) • Gases exert pressure (balloons, wind,atmosphere) • Collisions of gas particles are perfectly elastic

  3. Gases, cont. • In order to describe a gas completely, four variables must be considered: • n = amount of gas (moles) • V = volume of gas (Liters) • T = temperature of the gas (Kelvin) • P = pressure of/on the gas (usually atm) • 1 atm = 101,325 Pa = 760 mmHg = 760 torr = 14.7 psi = 1.013 bar • STP = standard temp. & pressure (0°C and 1 atm)

  4. Atmospheric Pressure • There is 7 miles of air above us. • Since gases have mass, that air creates pressure. • Many things on earth appear and/or function the way they do because of atmospheric pressure.

  5. Boyle’s Law • Inverse relationship between pressure and volume • With temp. constant, as pressure of a gas increases, the volume decreases (and vice versa) • P1 x V1 = k • P2 x V2 = k • So, P1V1 = P2V2

  6. Charles’ Law • Direct relationship between volume and temperature. • As the temperature of a gas increases, the volume increases; if pressure is constant. • V1÷ T1 = k • V2 ÷ T2 = k • So, (V1 ÷ T1) = (V2 ÷ T2)

  7. Dalton’s Law of Partial Pressures • Pertains to mixtures of gases. • The sum of the partial pressures of all the component gases in a mixture is equal to the total pressure of the mixture. • PT = p1 + p2 + p3 …..

  8. Avogadro’s Law • Equal volumes of different gases at the same temp. and pressure contain equal numbers of particles (equal # of moles) • Volume is directly proportional to # of moles. • V1÷ n1 = V2÷ n2 • 1 mole of any gas at STP occupies 22.4L of volume.

  9. Combined Gas Law • Necessary when two of the variables are changing. • P1V1 = P2V2 T1 T2

  10. Ideal Gas Law • To calculate the # of moles of a contained gas requires an expression that has the variable n. • The four previous laws can be combined to work with any gas in almost any situation. • PV = nRT • R = ideal gas constant • R = 0.0821 (L∙atm)/(K∙mol)

  11. Graham’s Law of Effusion • As stated earlier, gases travel easily through one another. Why? • Gases of lower molar mass diffuse/effuse faster than gases of higher molar mass. • In other words, light molecules travel through air more easily than heavy ones. • Mathematically you can compare the rate of diffusion of two gases as a ratio between the molar masses of the two gases.

  12. So, which gas would effuse/diffuse faster, hydrogen (H2)or sulfur hexafluoride (SF6)? • Which gas would effuse/diffuse faster, hydrogen (H2) or oxygen (O2)? • You can be more precise than that: How much faster would hydrogen travel through air than oxygen?

  13. What to Know for Gas Laws Test • Know your notes, and all of the new vocabulary • Have each of the gas laws memorized, by name and by formula • After reading a problem, recognize what gas law to use to solve it.

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