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GASES

GASES. General Properties of Gases. There is a lot of “free” space in a gas. Gases can be expanded infinitely. Gases fill containers uniformly and completely. Gases diffuse and mix rapidly. Properties of Gases. Gas properties can be modeled using math. Model depends on —

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GASES

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  1. GASES

  2. General Properties of Gases • There is a lot of “free” space in a gas. • Gases can be expanded infinitely. • Gases fill containers uniformly and completely. • Gases diffuse and mix rapidly.

  3. Properties of Gases • Gas properties can be modeled using math. Model depends on— • V = volume of the gas (L, mL) • T = temperature (K) • ALL temperatures in the entire chapter MUST be in Kelvin!!! No Exceptions! • n = amount (moles) • P = pressure (atmospheres, mmHg, torr, kPa)

  4. Pressure • Column height measures Pressure of atmosphere • 1 standard atmosphere (atm) * • = 760 mm Hg (or torr) * • = 101.3 kPa (SI unit is PASCAL)

  5. Pressure conversions • A.) What is 475 mm Hg expressed in atm? • 475 mmHg 1 atm = 0.625 atm 760 mm Hg • B.) The pressure of a tire is measured as 29.4 psi. What is this pressure in mm Hg? • 29.4 psi 760 mmHg = 1.52 x 103 mmHg 14.7 psi

  6. Your Turn: Learning Check for Pressure Conversions • A.) What is 2 atm expressed in torr? • B.) The pressure of a tire is measured as 32.0 psi. What is this pressure in kPa?

  7. Boyle’s Law • This means Pressure and Volume are INVERSELY PROPORTIONAL if moles and temperature are constant (do not change). For example, P goes up as V goes down. • P1V1 = P2 V2 • V1 is the original volume • V2 is the new volume • P1 is original pressure • P2 is the new pressure • Sample Problem • Suppose you have a gas with 45.0 ml of volume and has a pressure of 760.mmHg. If the pressure is increased to 800mmHg and the temperature remains constant then according to Boyle's Law the new volume is 42.8 ml. • (760mmHg)(45.0ml) = (800mmHg)(V2) • V2 = 42.8ml Robert Boyle

  8. Charles’s Law • V and T are directly proportional. If one temperature goes up, the volume goes up! • V1 V2 T1 = T2 • V1 is the initial volume T1 is the initial temperature • V2 is the final volume T2 is the final temperature • Sample Problem • You have a gas that has a volume of 2.5 liters and a temperature of 250 K. What would be the final temperature if the gas has a volume of 4.5 liters? • V1 / T1 = V2 / T2 • V1 = 2.5 liters • T1 = 250 K • V2 = 4.5 liters • T2 = ? • Solving for T2, the final temperature equals 450 K. • Important: Charles's Law only works when the pressure is constant. • Note: Charles's Law is fairly accurate but gases tend to deviate from it at very high and low pressures. Jacques Charles

  9. Gay-Lussac’s Law • If n and V are constant, then P α T • P and T are directly proportional. • P1 P2 T1 T2 • If one temperature goes up, the pressure goes up! • Sample problem • The pressure inside a container is 770 mmHg at a temperature of 57 C. What would the pressure be at 75 C? • P1= 770 mmHg • T1 = 57°C • T2= 75°C • P2 = ? =

  10. Combined Gas Law • Since they are all related to each other, we can combine them into a single equation. BE SURE YOU KNOW THIS EQUATION! P1 V1 P2 V2 T1 T2 =

  11. Combined Gas Law Problem • A sample of helium gas has a volume of 0.180 L, a pressure of 0.800 atm and a temperature of 29°C. What is the new temperature(°C) of the gas at a volume of 90.0 mL and a pressure of 3.20 atm? • Set up Data Table • P1 = 0.800 atm V1 = 180 mL T1 = 302 K • P2 = 3.20 atm V2= 90 mL T2 = ??

  12. Calculations • P1 = 0.800 atm V1 = 180 mL T1 = 302 K • P2 = 3.20 atm V2= 90 mL T2 = ?? • P1 V1 P2 V2 T1 = T2 P1 V1 T2 = P2 V2 T1 • T2 = P2 V2 T1 P1 V1 • T2 = 3.20 atm x 90.0 mL x 302 K0.800 atm x 180.0 mL • T2 = 604 K - 273 = 331 °C

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