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Gas Laws Pt.2

Gas Laws Pt.2. Honors Chemistry. Combined Gas Law. The Combined Gas Law Deals with the situation where only the number of molecules stays constant. P 1 x V 1 = P 2 x V 2 T 1 T 2 Lets us figure out one thing when two of the others change.

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Gas Laws Pt.2

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  1. Gas Laws Pt.2 Honors Chemistry

  2. Combined Gas Law • The Combined Gas Law Deals with the situation where only the number of molecules stays constant. • P1 x V1 = P2 x V2T1 T2 • Lets us figure out one thing when two of the others change.

  3. The combined gas law contains all the other gas laws! • If the temperature remains constant. P1 V1 P2 x V2 x = T1 T2 Boyle’s Law

  4. The combined gas law contains all the other gas laws! • If the pressure remains constant. P1 V1 P2 x V2 x = T1 T2 Charles’ Law

  5. The combined gas law contains all the other gas laws! • If the volume remains constant. P1 V1 P2 x V2 x = T1 T2 Gay-Lussac’s Law

  6. Examples • A 15 L cylinder of gas at 4.8 atm pressure at 25ºC is heated to 75ºC and compressed to 17 atm. What is the new volume?

  7. Examples • If 6.2 L of gas at 723 mm Hg at 21ºC is compressed to 2.2 L at 4117 mm Hg, what is the temperature of the gas?

  8. The Fourth Part • Avagadro’s Hypothesis • V is proportional to number of molecules at constant T and P. • V is proportional to moles. • V = K n ( n is the number of moles) • Gets put into the combined gas law • P1 x V1 = P2 x V2n1 x T1 n1 x T2 = K = R

  9. The Ideal Gas Law • P x V = n x R x T • Pressure times Volume equals the number of moles times the Ideal Gas Constant (R) times the temperature in Kelvin. • This time R does not depend on anything, it is really constant

  10. The Ideal Gas Constant • R = 0.0821 (L atm) (mol K) • R = 62.4 (L mm Hg) (K mol) • R = 8.31 (L kPa) (K mol)

  11. The Ideal Gas Law • PV = nRT • We now have a new way to count moles of a gas. By measuring T, P, and V. • We aren’t restricted to STP. • n = PV/RT • Nothing is required to change, • No 1’s and 2’s

  12. Example • How many moles of air are there in a 2.0 L bottle at 19ºC and 747 mm Hg?

  13. Example • What is the pressure exerted by 1.8 g of H2 gas exert in a 4.3 L balloon at 27ºC?

  14. Density • The Molar mass of a gas can be determined by the density of the gas. • D= mass = m Volume V • Molar mass = mass = m Moles n • n = PV RT

  15. Molar Mass = m (PV/RT) • Molar mass = m RT V P • Molar mass = DRT P

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