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Using the Gas Laws A Directed Learning Activity for Hartnell College Chemistry 1 Funded by the Title V – STEM Grant #P031S through Hartnell College For information contact Start

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Student Learning Objectives This tutorial will help you to: 1. Manipulate the ideal gas laws to calculate pressure, volume, temperature and amount of gas present & 2. Use balanced equations and the ideal gas laws to predict the amounts of reagents and/or products for gaseous reactions Next

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Getting Started This set of Power Point slides will lead you through a series of short lessons and quizzes on the topics covered by this Directed Learning Activity tutorial. Move through the slideshow at your own pace. There are several hyperlinks you can click on to take you to additional information, take quizzes, get answers to quizzes, and to skip to other lessons. You can end this slide show at any time by hitting the ESC key on your computer keyboard. Next

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Table of Topics What You Should Already Know Boyles Law Charles Law Gay-Lussacs Law Combined Gas Law Avogadros Law Ideal Gas Law Putting it All Together (Gas Stoichiometry) Daltons Law of Partial Pressures Next

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What You Should Already Know How to manipulate algebraic equations Conversions between different measurement units The basics of the Kinetic Molecular Theory of ideal gases Understand the mole Write balanced chemical equations for reactions If you are uncertain about these skills, please refer to your lecture text for help. Next

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Boyles Law Next

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Example 1 for Boyles Law 1. A sample of an ideal gas occupies 2.00 L at 760 torr. What volume will this amount of gas occupy if the temperature remains constant but the pressure changes to 1.25 atm? Remember that 1 atm = 760 torr. Solution: use Boyles law and substitute in the values for conditions 1 and 2. Property12 P760 torr = 1 atm 1.25 atm V2.00 L? Next

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Example 1 for Boyles Law (contd) Next

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Example 2 for Boyles Law A 1.00 L sample of an ideal gas at 760 torr is compressed to L at constant temperature. Calculate the final pressure of the gas. Solution: use Boyles law and substitute in the values for conditions 1 and 2. Property12 P760 torr = 1 atm ? V1.00 L0.800 L Next

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Example 2 for Boyles Law (contd) Next

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Quiz Question 1 A mass of oxygen occupies 7.00 L under a pressure of 740 torr. Determine the volume of the same mass of gas at the standard pressure of 760 torr, the temperature remaining constant. Check answerClick to review

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Answer to Quiz Question 1 Next question Click to review

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Quiz Question 2 Ten (10.0) liters of hydrogen under 7.0 atm pressure is slowly compressed until it occupies only 4.0 L of volume. Assume that the temperature of the gas remains constant. What pressure is needed for the gas to remain compressed? Check answerClick to review

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Solution to Quiz Question 2 Next lessonClick to review

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Charles Law Next

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Example for Charles Law A given mass of chlorine gas occupies 25.0 L at 20 °C. What is the new volume at 45 °C, assuming that the pressure remains constant? Solution: Use Charles Law and substitute the values for conditions 1 and 2. Remember temperature must be in Kelvin. Property12 V25.0 L? T K K Next

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Example for Charles Law (contd) Next

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Quiz Question 3 A sample of gaseous argon is maintained at a constant pressure. The sample has an initial volume of 10.5 L at 25 °C. What will be volume be if the same sample is kept at the same pressure, but heated to 250 °C? Check answerClick to review

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Answer to Quiz Question 3 Next questionClick to review

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Quiz Question 4 A certain amount of gas occupies of volume of 100. mL at a temperature of 20 °C. What will the new volume be at 10 °C, if the pressure remains constant? Check answerClick to review

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Answer to Quiz Question 4 Next lesson Click to review

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Gay-Lussacs Law Next

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Example for Gay-Lussacs Law The air in a cylindrical tank has a pressure of 640 torr at 23 °C. When the tank was placed in the sun, the temperature rose to 48 °C. What was the final pressure in the tank if the mass and volume of the gas does not change? Solution : Use Gay-Lussacs Law. Remember that temperature must be in Kelvin. Property12 P640 torr? T K K Next

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Example for Gay-Lussacs Law (contd) Next

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Quiz Question 5 A sealed glass bulb contains a sample of He gas at a pressure of 750 torr and 27 °C. The bulb was cooled down to -73 °C. What was the new gas pressure inside the bulb? Check answerClick to review

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Answer to Quiz Question 5 Next questionClick to review

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Quiz Question 6 A steel tank contains carbon dioxide gas at 27 °C and at a pressure of 11.0 atm. Determine the internal pressure when the gas and its contents are heated to 100 °C. Assume that the amount of carbon dioxide and the volume of the tank are constant. Check answer Click to review

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Answer to Quiz Question 6 Next lessonClick to review

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The Combined Gas Law Next

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Example for the Combined Gas Law What would be the new pressure for a 2.00 L sample of gas at 1.00 atm and -20 °C that is compressed to a new volume of L at 40 °C? Solution: Use the combined gas law. Temperatures must be converted to Kelvin. 12 P1.00 atm? V2.00 L K T0.500 L K Next

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Example for the Combined Gas Law (contd) Next

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Quiz Question 7 A 2.50 L sample of gas is at 0 °C and 1.00 atm pressure. What will the temperature of the gas be if it is placed in a 2.00 L container at 1.50 atm pressure? Check answer Click to review

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Answer to Quiz Question 7 Next lessonClick to review

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Avogadros Gas Law Under Standard Temperature and Pressure (STP) conditions, the volume of one mole of an ideal gas will occupy Liters. 1 mole ideal gas = L, at STP STP conditions are 273K and 1 atmosphere (760 mm Hg) of pressure. Next lesson

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The Ideal Gas Law To adequately describe an ideal gas under a particular set of physical conditions, you need to know: the temperature, pressure and volume of the gas; and the amount of gas. This is summarized in the following equation: Next

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The Ideal Gas Law contd Next

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Example for the Ideal Gas Law What is the pressure in atmospheres of 3.4x10 -3 moles of argon gas in a 75-mL glass bulb at 20 °C? Solution: The problem gives three out of the four properties of an ideal gas (moles, volume, and temperature) and asks for the fourth (pressure). Use the Ideal Gas Law. Next

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Example for Ideal Gas Law contd Next

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Quiz Question 8 An incandescent light bulb contains g of Ar in a 23.0-mL volume. The pressure inside the light bulb under these conditions is 952 torr. What is the temperature of the Ar gas under these conditions? Check answerClick to review

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Answer to Quiz Question 8 Next lessonClick to review

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Putting it All Together – Gas Stoichiometry If we are given a chemical reaction where one or more of the reactants is a gas, we can use the balanced chemical equation to determine the volume of gas that is obtained if we know the amounts of the reagents. If we know the experimental conditions of temperature and pressure, we can use the Ideal Gas Law. Often problems like this are written to be solved under STP conditions, so the results of Avogadros Law can also be used. This kind of problem is sometimes called gas stoichiometry. Lets look at an example. Next

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Example Problem How many liters of carbon dioxide at STP will be formed from the complete combustion of g of ethanol, C 2 H 5 OH(l)? What would this volume be if we then changed the conditions of the gas to 23 °C and 0.95 atm to expand the gas after formation? Solution: First we need to write the balanced equation for the reaction. C 2 H 5 OH(l) + 3 O 2 (g) 2 CO 2 (g) + 2 H 2 O(l) Next, we need to know how many moles of ethanol we have as starting material. This will allow us to use this procedure: g C 2 H 5 OH mol C 2 H 5 OH mol CO 2 L CO STP For the last step, since the conditions are at STP, we know that each mole of CO 2 = L. If the conditions are different than STP, we have to use the Ideal Gas Law to determine the volume. Next

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Example Problem contd Next

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Quiz Question 9 Calculate the volume of O 2 that can be prepared at 60 °C and 760 torr by the decomposition of 20.0 g H 2 O 2 to H 2 O and O 2. The reaction is: 2 H 2 O 2 2 H 2 O + O 2. Check answerClick to review

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Answer to Quiz Question 9 Next

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Answer to Quiz Question 9 contd Next lessonClick to review

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Daltons Law of Partial Pressures Next

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Example Using Daltons Law 3.00L oxygen gas is collected over water at 27 °C and when the barometric pressure is 787 torr. The vapor pressure of water at 27 C is 27 torr. What is the partial pressure of the dry oxygen gas under these conditions? Solution: P O2 = P total – P H2O = 787torr – 27torr = 760torr Next

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Quiz Question 10 Exactly 100 mL of oxygen gas is collected over water at 23 °C and 800 torr. Calculate the standard volume of the dry oxygen if the vapor pressure of water at 23 °C is 21.1 torr. Check answerClick to review

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Answer to Quiz Question 10 Solution: V 2 = 94.5 mL Explanation: We first use Daltons Law to find the partial pressure of oxygen P O2 = P total – P H20 = 800torr – 21.1torr = 779torr Next

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Solution to Quiz Question 10 contd 12 P779 torr760 torr V100. mL? T You must then use the combined gas law to determine the volume of the oxygen at STP. Here is what you know. Next

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Solution to Quiz Question 10 contd NextClick to review

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Congratulations! You have successfully completed this Directed Learning Activity tutorial. We hope that this has helped you to better understand this topic. Click here to end.here Click here to repeat this activity.here

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This document has been prepared in compliance with US & International Copyright Laws © 2011 Hartnell College Funded by the Title V – STEM Grant #P031S through Hartnell College Information Hit the ESC key to end this slide show

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