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Chemistry Gases Dalton’s Law of Partial Pressures & Ideal Gas Law

Chemistry Gases Dalton’s Law of Partial Pressures & Ideal Gas Law. CALCULATORS NEEDED PERIODIC TABLES NEEDED. Dalton’s Law of Partial Pressures. If you have a gas mixture, the total pressure equals the sum of the pressures that each individual gas would exert if it were present alone.

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Chemistry Gases Dalton’s Law of Partial Pressures & Ideal Gas Law

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  1. ChemistryGasesDalton’s Law of Partial Pressures & Ideal Gas Law CALCULATORS NEEDED PERIODIC TABLES NEEDED

  2. Dalton’s Law of Partial Pressures • If you have a gas mixture, the total pressure equals the sum of the pressures that each individual gas would exert if it were present alone. • In other words.. Ptotal = P1 + P2 + P3 + …

  3. Practice Problem • Three of the primary components of air are carbon dioxide, nitrogen, and oxygen. In a sample containing a mixture of only these gases at exactly 1 atm, the partial pressures of carbon dioxide and nitrogen are given as PCO2 = 0.285 torr and PN2 = 593.525 torr. What is the partial pressure of oxygen?

  4. Gas Collection • If you collect gas over water, there is some water vapor mixed in with the gas due to evaporation. • To find only the desired gas, you must subtract the vapor pressure of water from the total pressure. • Pgas + VPwater = Ptotal

  5. Practice Problem • Oxygen gas from the decomposition of potassium chlorate, KClO3, was collected by water displacement. The barometric pressure and the temperature during the experiment were 731.0 torr and 20.0oC, respectively. What was the partial pressure of the oxygen collected?

  6. Avogadro’s Law • There is a fourth basic gas law, but it is only used to make a combined version of all the gas laws called the ideal gas law. • Avogadro’s law says that the volume of gas increases as the amount of gas increases (moles). • Moles = n

  7. Ideal Gas Law • If we look at the four equations, we see common elements: • P and V in the numerator • T and n in the denominator • In science, when we combine these gas laws mathematically, we can say that they are equal to a constant… • Constant = number that doesn’t change • R = ideal gas constant • PV = nRT (Ideal Gas Law)

  8. Ideal Gas Law • If we simplify the equation, we get the ideal gas law: • PV = nRT • Volume must be in liters • Temperature must be in Kelvin • Pressure units can be different, and they determine the value of R

  9. Units of the Ideal Gas Constant R If pressure is in units of… R equals… Atmospheres: 0.0821 (L-atm)/(mol-K) Torr/mm Hg: 62.4 (L-torr)/(mol-K) Kilopascals: 8.31 (L-kPa)/(mol-K) or J/(mol-K)

  10. A deep underground cave contains 2.24 x 106 L of methane gas (CH4) at a pressure of 1,500 kPa and a temperature of 315 K. How many moles of CH4 does this cavern contain? How many kilograms of CH4 does this cavern contain? Sample Problem

  11. Ideal Gas Law and Density • We can use the ideal gas law to determine the density of a gas. (M = molar mass) • One only needs to know the molar mass, pressure, and temperature to calculate the density of a gas.

  12. Practice • The density of an unknown gas is 4.20 grams per liter at 3.00 atmospheres pressure and 127 ºC. What is the molar mass of this gas?(R = 0.0821 liter-atm/mole-K)

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