Thursday February 28, 2013 (Dalton’s Law of Partial Pressures and Avogadro’s Law)

What instrument is used to measure atmospheric pressure? A barometer Show the equation that equates the eight units of standard atmospheric pressure. 760 mmHg= 760 torr= 1 atm = x 10 5 Pa= kPa = in Hg= millibars = 14.7 psi

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Assignment Currently Open Summative or Formative? Date Issued Date Due Date Into GradeSpeed Final Day QUIZ 19S42/15 TOMORROW WS – The Nature of Gases F192/202/21 TOMORROW QUIZ 20S52/22 3/8 TELPAS Writing Sample F12/253/1 TOMORROW WS – Gas Pressure and Force F22/262/28 TOMORROW WS – Measuring Pressure and Units of Pressure F32/273/1 3/8

John Dalton, the English chemist who proposed the atomic theory, also studied gas mixtures. He found that in the absence of a chemical reaction, the pressure of a gas mixture is the sum of the individual pressures of each gas alone. Dalton’s Law of Partial Pressures

This picture shows a 1.0 L container filled with oxygen gas at a pressure of 0.12 atm at 0°C. In another 1.0 L container, an equal number of molecules of nitrogen gas exert a pressure of 0.12 atm at 0°C. The gas samples are then combined in a 1.0 L container. (At 0°C, oxygen gas and nitrogen gas are unreactive.) The total pressure of the mixture is found to be 0.24 atm at 0°C. The pressure that each gas exerts in the mixture is independent of that exerted by other gases present. The pressure of each gas in a mixture is called the partial pressure of that gas. Dalton’s Law of Partial Pressures

Dalton’s law of partial pressures states that the total pressure of a mixture of gases is equal to the sum of the partial pressures of the component gases. The law is true regardless of the number of different gases that are present. Dalton’s law may be expressed as follows: P T = P 1 + P 2 + P PT is the total pressure of the mixture. P1, P2, P3,... are the partial pressures of component gases 1, 2, 3, and so on. Dalton’s Law of Partial Pressures

Sample Problem Three of the primary components of air are carbon dioxide, nitrogen, and oxygen. In a sample containing a mixture of only these three gases at exactly one atmosphere pressure, the partial pressures of carbon dioxide (P CO2 ) = torr and nitrogen (P N2 ) = torr. What is the partial pressure of oxygen? Dalton’s Law of Partial Pressures P T = P 1 + P 2 + P P air = P CO 2 + P N 2 + P O 2 P air = 1 atm = torr torr = torr torr + P O 2 P O 2 = – – = torr

Avogadro’s Law In 1811, Amedeo Avogadro hypothesized that two given samples of an ideal gas, of the same volume and at the same temperature and pressure, contain the same number of molecules. Thus, the number of molecules or atoms in a specific volume of gas is independent of their size or the molar mass of the gas. As an example, equal volumes of molecular hydrogen and nitrogen contain the same number of molecules when they are at the same temperature and pressure, and observe ideal gas behavior.

Avogadro’s Law Consider the reaction of hydrogen and chlorine to produce hydrogen chloride. According to Avogadro’s law, equal volumes of hydrogen and chlorine contain the same number of molecules. H 2 + Cl 2 → 2HCl 1 volume 1 volume 2 volumes 1 molecule 1 molecule 2 molecules

Avogadro’s Law Avogadro’s law also indicates that gas volume is directly proportional to the amount of gas, at a given temperature and pressure. Note the equation for this relationship. V = kn Here, n is the amount of gas, in moles, and k is a constant.

Worksheet Dalton’s Law (Partial Pressures) Avogadro’s Law (Same V,T,&P – Same Number of Molecules)