HW07-key

# HW07-key - Chemistry 111 Homework#7 KEY Due(Wednesday 1 A...

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Chemistry 111 Homework #7 - KEY Due: October 19, 2005 (Wednesday) 1. A sample of carbon dioxide gas (CO 2 ) is placed in a small 450 mL flask, with very strong walls, under a pressure of 10.0 atm at -11°C. What is the mass of CO 2 in that flask? a) 9,205 g b) 12.5 g c) 9.20 g d) 8.49 g e) 219 g f) None of these. This problem involves a single state for a gaseous substance. Assuming that the gas behaves ideally: P V = ( g R T) / MW. 10.0atm × 0.450 L = g × 0.0821Latm / Kmol × 262K 44.0 g / mol g = 9.20 g . 2. A particular experiment calls for CO 2 gas with a density of 4.32 g/L at a pressure of 3.23 atm. What will be the temperature for the sample of CO 2 gas that has this density and pressure? a) 128°C b) 401°C c) 674°C d) 25°C e) 263°C f) 225°C Here you want to use the equation for density of an ideal gas. density = P × MW R T Substituting the values, we get: 4.32g / L = 3.23atm × 44.0 g / mol 0.0821Latm / Kmol × T T = 401 K or 128°C . 3. An unknown gas has a density of 2.59 g/L at STP. Identify the gas. a) NO 2 b) O 2 c) CO 2 d) CO e) C 2 H 6 f) C 4 H 10

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Chemistry 111 2 Homework #7 / Fall 2005 Once again, you want to use the density form of the ideal gas equation, but solve for the molecular weight: density = P × MW R T Substituting the values, we get: 2.59 g / L = 1.00atm × MW 0.0821Latm / Kmol × 273K = 58.1 g/mol Æ C 4 H 10 4. How many of the following are properties of an ideal gas? Type your numerical answer in Blackboard. 1. It consists of particles that have no volume. 2. It consists of particles that have no attractive nor repulsive forces for each other. 3. It is made up of particles that are in constant, random motion. 4. It can be readily liquefied at high pressures and low temperatures. 5. It obeys PV = nRT. The only one that is not is #4. In order to be liquefied, we would have to acknowledge the existence of intermolecular forces of attraction. Therefore, the answer is… 4 . 5. According to the postulates of the kinetic molecular theory of gases, the average speed of the molecules in a given gas is proportional to the… a) absolute temperature squared. b) absolute temperature. c) reciprocal of the absolute temperature. d) Celsius temperature squared. e) the square root of the absolute temperature. f) None of these. 6. Consider the following reaction… N 2 (g) + 3 H 2 (g) 2 NH 3 (g) How many liters of NH 3, measured at 100°C and 725 torr, can be produced from 25.0 L of H 2 measured at 300°C and 525 torr?
Chemistry 111 3 Homework #7 / Fall 2005 a) 11.8 L b) 11.0 L c) 4.75 L d) 7.13 L e) 7.86 L f) None of these. Here we need to use the stoichiometry of the reaction. We are given the volume, the temperature and the pressure of the hydrogen gas sample (one of the reagents). Therefore, we actually know the moles of hydrogen… molesof H 2 = P V R T n H 2 = 0.691atm × 25.0 L 0.0821Latm / Kmol × 573K = 0.367 moles of hydrogen gas. Now, how do these moles of hydrogen gas relate to the moles of ammonia formed theoretically? We can tell using the coefficients from the balanced reaction.

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## This note was uploaded on 02/08/2010 for the course CHEM 111 taught by Professor Kenney during the Spring '08 term at Case Western.

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HW07-key - Chemistry 111 Homework#7 KEY Due(Wednesday 1 A...

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