Gay Lussacs law of combining volumes of gases

Gay Lussac’s law of combining volumes of gases • When gases combine, they combine in simple whole number ratios. • These simple numbers are the coefficients of the balanced equation. N 2 + 3 H 2 2 NH 3 • 3 volumes of hydrogen will produce 2 volumes of ammonia Mullis 1

Avogadro’s Law and Molar Volume of Gases • Equal volumes of gases (at the same temp and pressure) contain an equal number of molecules. In the equation for ammonia formation, 1 volume N 2 = 1 molecule N 2 = 1 mole N 2 • One mole of any gas will occupy the same volume as one mole of any other gas • Standard molar volume of a gas is the volume occupied by one mole of a gas at STP. Standard molar volume of a gas is 22. 4 L. Mullis 2

Sample molar volume problem • A chemical reaction produces 98. 0 m. L of sulfur dioxide gas at STP. What was the mass, in grams, of the gas produced? ***Turn m. L to L first! (This way, you can use 22. 4 L) 98 m. L 1000 m. L 1 mol SO 2 64. 07 g SO 2 = 0. 280 g SO 2 22. 4 L 1 mol SO 2 Mullis 3

Sample molar volume problem 2 What is the volume of 77. 0 g of nitrogen dioxide gas at STP? 77. 0 g NO 2 1 mol NO 2 22. 4 L 46. 01 g NO 2 1 mol NO 2 Mullis = 37. 5 L NO 2 4

Ideal Gas Law • Mathematical relationship for PVT and number of moles of gas PV = n. RT n = number of moles R = ideal gas constant P = pressure V = volume in L T = Temperature in K R = 0. 0821 if pressure is in atm R = 8. 314 if pressure is in k. Pa R = 62. 4 if pressure is in. Mullis mm Hg 5

Sample Ideal Gas Law Problem • What pressure in atm will 1. 36 kg of N 2 O gas exert when it is compressed in a 25. 0 L cylinder and is stored in an outdoor shed where the temperature can reach 59°C in summer? V = 25. 0 L T = 59+273 = 332 K P = ? R = 0. 0821 L-atm n = 1. 36 kg converted to moles mol-K • 1. 36 kg N 2 O 1000 g 1 mol N 2 O = 30. 90 mol N 2 O 1 kg 44. 02 g N 2 O • PV = n. RT • P = 30. 90 mol x 0. 0821 L-atm x 332 K = 33. 7 atm 25. 0 L mol-K Mullis 6

Volume-Volume Calculations • Volume ratios for gases are expressed the same way as mole ratios we used in other stoichiometry problems. N 2 + 3 H 2 2 NH 3 Volume ratios are: 2 volumes NH 3 3 volumes H 2 1 volume N 2 Mullis 7

Sample Volume-Volume Problem • How many liters of oxygen are needed to burn 100 L of carbon monoxide? 2 CO + O 2 2 CO 2 100 L CO 1 volume O 2 2 volume CO Mullis = 50 L O 2 8

Sample Volume-Volume Problem 2 Ethanol burns according to the equation below. At 2. 26 atm and 40° C, 55. 8 m. L of oxygen are used. What volume of CO 2 is produced when measured at STP? C 2 H 5 OH + 3 O 2 2 CO 2 + 3 H 2 O Number moles oxygen under these conditions is? PV = n. RT: 2. 26 atm(. 0558 L) = n = 0. 0049 mol O 2 (0. 0821 L-atm)(313 K) mol-K 0. 0049 mol O 2 2 mol CO 2 22. 4 L =0. 073 L CO 2 3 mol O 2 1 mol CO 2 Mullis 9