1. Mullis1 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 + 3H 2 2NH 3 3 volumes of hydrogen will produce 2 volumes of ammonia

2. Mullis2 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.

3. Mullis3 Sample molar volume problem A chemical reaction produces 98.0 mL of sulfur dioxide gas at STP. What was the mass, in grams, of the gas produced? ***Turn mL to L first! (This way, you can can use 22.4 L) 98 mL 1 L 1 mol SO 2 64.07g SO 2 = 0.280g SO 2 1000 mL 22.4 L 1 mol SO 2

4. Mullis4 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 = 37.5 L NO 2 46.01g NO 2 1 mol NO 2

5. Mullis5 Ideal Gas Law Mathematical relationship for PVT and number of moles of gas PV = nRT 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 kPa R = 62.4 if pressure is in mm Hg

6. Mullis6 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 LT = 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 = nRT P = 30.90 mol x 0.0821 L-atm x 332 K= 33.7 atm 25.0 L mol-K

7. Mullis7 Volume-Volume Calculations Volume ratios for gases are expressed the same way as mole ratios we used in other stoichiometry problems. N 2 + 3H 2 2NH 3 Volume ratios are: 2 volumes NH 3 3 volumes H 2 2 volumes NH 3 3 volumes H 2 1 volume N 2 1 volume N 2

8. Mullis8 Sample Volume-Volume Problem How many liters of oxygen are needed to burn 100 L of carbon monoxide? 2CO + O 2 2CO 2 100 L CO 1 volume O 2 = 50 L O 2 2 volume CO

9. Mullis9 Sample Volume-Volume Problem 2 Ethanol burns according to the equation below. At 2.26 atm and 40° C, 55.8 mL of oxygen are used. What volume of CO 2 is produced when measured at STP? C 2 H 5 OH + 3O 2 2CO 2 + 3H 2 O Number moles oxygen under these conditions is? PV = nRT: 2.26 atm (.0558 L ) = n = 0.0049 mol O 2 ( 0.0821 L-atm )(313K ) 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