GASES

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Dr. Kittisak ChoojunDepartment of Chemistry,Faculty of Science, KMITL

Ref: Ralph H. Petrucci, F. ed. Geoffrey Herring, Jeffry D. Madura, Carey Bissonnette. General Chemistry: Principles and Modern Applications. Prentice Hall 2010, English 10th ed. Theodore E. Brown, H. Eugene H LeMay, Bruce E. Bursten, Catherine Murphy, Patrick Woodward. Chemistry: The Central Science. Prentice Hall 2011, English 12th ed. Raymond Chang and Jason Overby. General Chemistry: The Essential Concepts. McGraw-Hill Science/Engineering/Math 2010, 6th

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Elements that exist as gases at 25 0C and 1 atmosphere

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Properties of Gases - Gases expand to fill their containers and assume the shapes of their

containers. (กาซมรปรางตามภาชนะ) - They diffuse into one another and mix in all proportions. (มการแพรและ

เกดการผสมได)

- There are four properties that we use in order to explain the physical behavior of a gas: the amount of the gas (in moles), volume, temperature, and pressure. (ส=คณสมบตหลกท=ใชในการอธบายสมบต

กายภาพของกาซ คอ จานวนโมล ปรมาตร อณหภม และความดน)

- If we know any three of these, we can usually calculate the value of the remaining one.

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The Concept of Pressure- Molecules of a gas are in constant motion, frequently colliding with

one another and with the walls of their container. In their collisions, the gas molecules exert a force on the container walls.

- Pressure (P) is defined as a force per unit area. - In SI, the unit of force is a Newton (N) 1 N = 1 kg m s-2 , the unit

of pressure is pascal (Pa).

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Liquid Pressure- Due to the difficulty to measure the pressure directly in gas state, scientists have

measured the pressure of gas indirectly using a liquid pressure. (ยากท=จะหาความดนกาซ

จากสถานะกาซโดยตรงจงใชความดนของของเหลวมาชวย)

- Liquid pressure is directly proportional to the liquid density and the height of the liquid column.

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Barometric Pressure

In 1643, Evangelista Torricelli constructed the device called barometer. ---> Barometric pressure (mmHg)-Typically the height of Hg is 760mm at sea level, density of Hg = 13.5951 g/cm3, g = 9.80655 m/s2 (โดยท=วไปท=ผวทะเล ความสงของปรอทในบารรอมเตอรคอ 760mm)

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Why did they use Hg rather than H2O? ทาไมถงใชปรอทแทนท=จะเปนนTาซ=งหาไดงายกวา

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Manometers

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If the atmospheric pressure is 0.995 atm, what is the pressure of the enclosed gas in each of the three cases depicted in the drawing? Assume that the gray liquid is mercury.

The Simple Gas LawsBoyle’s Law

Robert Boyle:For a fixed amount of gas at a constant temperature, the gas volume is inversely proportional to the gas pressure. (ปรมาตรของกาซแปรผกผนกบความดนของ

กาซ เม=อจานวนโมลและอณภมของกาซคงท=)

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The Simple Gas LawsCharles’s Law

Jacques Charles:The volume of gas increases as the temperature is raised and decreases as the temperature is lowered, at constant pressure and amount of gas. (ปรมาตรเพ=มเม=ออณหภมเพ=ม และลดเม=อ

อณหภมลด ภายใตสภาวะความดนและ

จานวนโมลของกาซคงท=)

Note: Using SrF à 0.0025K12

Standard Conditions of Temperature and Pressure

Standard conditions of temperature and pressure are usually abbreviated as STP, where T = 0oC = 273.15 K and P = 1 bar = 100 kPa = 105 Pa. The old day was based on P = 1 atm.

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The Simple Gas LawsAvogadro’s Law

Amedeo Avogadro:At a fixed temperature and pressure, the volume of a gas is directly proportional to the amount of gas. (ท=อณภมและความดนคงท=

ปรมาตรของกาซจะแปรผนตรง

กบจานวนกาซ)

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Combining the Gas Laws: The Ideal Gas Equation and the General Gas Equation

R = The Gas Constant

Give it a thought: How can you derive the value

of the gas constant? ลองคดหาคาคงท,ของกาซ

จากความรท,เรยนมา15

The General Gas Equation

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What is the volume occupied by 13.7 g Cl2(g) at 45oC and 745 mmHg?

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Calculate each of the following quantities for an ideal gas: (a) the volume of the gas, in liters, if 1.50 mol has a pressure of 1.25 atm at a

temperature of -6 °C (b) the absolute temperature of the gas at which 3.33 x 10-3 mol occupies 478 mL

at 750 torr(c) the pressure, in atmospheres, if 0.00245 mol occupies 413 mL at 138 °C (d) the quantity of gas, in moles, if 126.5 L at 54 °C has a pressure of 11.25 kPa.

A 1.27 g sample of an oxide of nitrogen, believed to be either NO or N2O, occupies a volume of 1.07 L at 25oC and 737 mmHg. Which oxide is it?

The density of a sample of gas is 1.00 g/L at 745 mmHg and 109oC. What is the molar mass of the gas?

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The adult blue whale has a lung capacity of 5.0 x 103 L. Calculate the mass of air (assume an average molar mass 28.98 g/mol) contained in an adult blue whale’s lungs at 0.0 °C and 1.00 atm, assuming the air behaves ideally.

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What volume of N2, measured at 735 mmHg and 26oC, is produced when 75.0 g NaN3 is decomposed?

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The first step in making nitric acid is to convert ammonia to nitrogen monoxide. This is done under conditions of high temperature and in the presence of a platinum catalyst. What volume of O2(g) is consumed per liter of NO(g) formed? (ข $นตอนแรกในการผลตกรดไนตรก ตองเปล8ยนกาซแอมโมเนยเปนกาซไนโตรเจนมอนอกไซด ปฏกรยาในข $นน $จะทาภาใตความรอนท8สงและมตวเรง

ปฏกรยาคอแพลทนม จงหาปรมาตรของกาซออกซเจนท8ใชตอลตรของกาซไนโตรเจนมอนอกไซดท8เกดข $น)

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Both Jacques Charles and Joseph Louis Guy-Lussac were avid balloonists. In his original flight in 1783, Jacques Charles used a balloon that contained approximately 31,150 L of H2. He generated the H2 using the reaction between iron and hydrochloric acid:

Fe(s) + 2 HCl(aq) à FeCl2(aq) + H2(g)

How many kilograms of iron were needed to produce this volume of H2 if the temperature was 22 °C ?

Mixtures of GasesThe simple gas laws and the ideal gas equation apply to a mixture of nonreactive gases as well as to individual gases. (กฏของกาซท=มชนดเดยว สามารถนามาใชในกาซผสมได)

John Dalton proposed that in a mixture, each gas expands to fill the container and exerts the same pressure (called its partial pressure) that it would if it were alone in the container. (ในกาซผสม กาซแตละชนดในกาซผสมทาตวเหมอนอยเปนอสละ และความดนรวมจะเทากบผลรวมความดนของกาซแต

ชนด)

Dalton’s law of partial pressures states that the total pressure of a mixture of gases is the sum of the partial pressures of the components of the mixtures:

Ptot = PA + PB + PC + …

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Mixtures of Gases

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A mixture of gases contains 0.75 mol N2, 0.30 mol O2, and 0.15 mol CO2. If thetotal pressure of the mixture is 2.15 atm, what is the partial pressure of eachcomponent?

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A deep-sea diver uses a gas cylinder with a volume of 10.0 L and a content of 51.2 g of O2 and 32.6 g of He. Calculate the partial pressure of each gas and the total pressure if the temperature of the gas is 19 °C.

Mixtures of Gases

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In the following reaction, 81.2 mL of O2(g) is collected over water at 23oC and barometric pressure 751 mmHg. What mass of Ag2O(s) decomposed?

2 Ag2O(s) à 4 Ag(s) + O2(g)

Kinetic-Molecular Theory of Gases

Kinetic-molecular theory of gases:- A gas is composed of a very large number of extremely small particles in constant,

random, straight-line motion. (กาซประกอบดวยอนภาคเลกมากๆและมจานวนมาก เคล=อนท=ดวยความเรว

คงท= ไมเปนทศทาง ในแบบเสนตรง)

- Molecules of a gas are separated by great distances. (point masses, no volume) (ระยะทาง

ระหวางโมเลกลของกาซมคาเยอะมาก จนคดไดวาโมเลกลของกาซเปนจดมวลและไมมปรมาตร)

- Molecules collide only fleetingly with one another and with the walls of their container, and most of the time molecules are not colliding. (โมเลกลของกาซมการชนกนและชนกบภาชนะแบบ

ช=วขณะ)

- There are assumed to be no forces between molecules except very briefly during collisions. Each molecule acts independently of all the others and is unaffected by their presence, except during collisions. (โมเลกลของกาซไมมแรงระหวางโมเลกล ยกเวนเวลาชนกน)

- Individual molecules may gain or lose energy as a result of collisions. In a collection of molecules at constant temperature; however, the total energy remains constant. (โมเลกล

ของกาซเกดการชนกนจะมการแลกเปล=ยนพลงงานกน แตพลงงานทTงหมดของระบบยงคงเทาเดม)

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Gas Properties Relating to the Kinetic-Molecular TheoryDiffusion is the migration of molecules as a result of random molecular motion. Effusion is the escape of gas molecules from their container through a tiny orifice or pinhole.

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Non-ideal (Real) GasesThe molecules of a gas occupy space; thus, the volume of the ideal gas is larger than the real gas.There are attractive forces between the gas molecules; therefore, the ideal gas has less pressure than the real gas.

The van der Waals Equation

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Use the van der Waals equation to calculate the pressure exerted by 1.00 mol Cl2(g) confined to a volume of 2.00 L at 273 K. The value of a = 6.49 L2 atm mol-2, and that of b = 0.0562 L mol-1. What is the %difference compared to the ideal gas?จงคานวณหาความดนของกาซคลอรน X.ZZ โมล ท=มปรมาตร [.ZZ ลตร อณหภม [\] K โดยใชสมการของกาซจรง โดยมคา

a และ b จากขางตน จงหา % ความแตกตางระหวางใชสมการของกาซจรงและกาซอดมคต

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Gaseous iodine pentafluoride, IF5, can be prepared by the reaction of solid iodine and gaseous fluorine:

I2(s) + 5 F2(g) à 2 IF5(g) A 5.00-L flask containing 10.0 g I2 is charged with 10.0 g F2, and the reaction proceeds until one of the reagents is completely consumed. After the reaction is complete, the temperature in the flask is 125 °C. (a) What is the partial pressure of IF5 in the flask? (b) What is the mole fraction of IF5 in the flask (c) Draw the Lewis structure of IF5. (d) What is the total mass of reactants and products in the flask?

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Cyclopropane, a gas used with oxygen as a general anesthetic, is composed of 85.7% C and 14.3% H by mass. (a) If 1.56 g of cyclopropane has a volume of 1.00 L at 0.984 atm and 50.0 °C,

what is the molecular formula of cyclopropane? (b) Judging from its molecular formula, would you expect cyclopropane to deviate

more or less than Ar from ideal-gas behavior at moderately high pressures and room temperature? Explain.

(c) Would cyclopropane effuse through a pinhole faster or more slowly than methane, CH4?