Lesson 9 Dalton's Law of Partial Pressures PDF

Lesson 9: Dalton’s Law of Partial Pressures  Most Essential Learning Competencies 1. Use Dalton’s law of partial pressures to relate mole fraction and partial pressure of gases in a mixture (STEM_GC11DLIi-47). 1-2 Many of the...

Lesson 9: Dalton’s Law of Partial Pressures  Most Essential Learning Competencies 1. Use Dalton’s law of partial pressures to relate mole fraction and partial pressure of gases in a mixture (STEM_GC11DLIi-47). 1-2 Many of the gases encountered in the surrounding are mixtures. The Ideal Gas Equation can also be applied to not only to pure gases, but also to mixtures of gases. 1-3 A system composed of three gases contained in a vessel of volume V and kept at a temperature T. The number of moles of each gas is n1, n2 and n3, for gases 1, 2 and 3, respectively, so that the total number of moles of gases is 1-4 The pressure of the mixture is given by the Ideal Gas Equation: Expressing ntotal in terms of the number of moles of each gas and solving for Pmixture will result in 1-5 If the right-hand side of the equation is expanded, the expression becomes The term ni R T / V is equal to P and see that the previous equation can be written as 1-6 The pressures P1, P2, and P3, called partial pressure of each gas, corresponds to the pressure that the gas will exert in a volume equal to that of the mixture. According to this expression, the total pressure of a gas mixture is equal to the sum of the partial pressure of each gas. This is known as Dalton’s Law of Partial Pressure. 1-7  Let’s Try 1. In a gas mixture composed of N2, Ne, and He, the partial pressure of N2 is 0.50 atm, that of Ne is 1.1 atm, and that of He is 0.80 atm. What is the total pressure of the mixture? Answer: 2.4 atm 1-8  Let’s Try 2. A sample of oxygen gas, which is saturated with water vapor, is kept in a 10.0-L vessel at 30.0oC and has a pressure of 758 Torr. If the pressure of the water vapor at this temperature is 31.8 Torr, what would be the pressure of the dry oxygen? Answer: 726 Torr 1-9 The application of Dalton’s Law can also yield information about the composition of the mixture, in terms of the mole fraction of each component. Write on the board the expression for the pressure of gas 1 and that of the mixture: 1-10 Dividing P1 by Pmixture gives the following expression: The term at the right-hand of the equation is actually a fraction, i.e. part divided the whole, and is known as mole fraction X1. Rearranging the expression leads to an important relationship: 1-11  Let’s Try 1. In a gas mixture composed of N2, Ne, and He, the partial pressure of N2 is 0.50 atm, that of Ne is 1.1 atm, and that of He is 0.80 atm. Calculate the mole fraction of each gas. Answer: N2: X = 0.21; Ne: X = 0.46; He: X = 0.33 1-12  Let’s Try 2. A gas mixture contains 2.5 mol N2 and 9.7 mol CO2, and has a pressure of 2.3 atm. What is the partial pressure of each gas? Answer: N2: P = 0.47 atm; CO2: P = 1.83 atm 1-13 1-14