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Gaseous State Chapter 9

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9.1 The Behavior of Gases

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Characteristics of Gas Gases consist of Particles that are relatively far apart Gas particles move very rapidly Gas particles have little interaction until they collide. Gases expand to fill the available space.

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Description of Gases Gases can be described in various physical properties. –Pressure –Temperature –Density –Volume –Number of Particles Changing one physical parameter will change one or more others.

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Pressure Pressure (P) = Force/area There are several units for Pressure. –Pounds/Sq. Inch (psi) –1 Atmosphere (atm) = 760 mm Hg = 760 torr –1 atm = 101,325 Pa (pascal) –1 atm = 14.7 psi

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EXAMPLE Calculate the amount of pressure a 105 lbs. woman exerts by stepping down on a stiletto heel (1/16 sq inch)? Compare this to an Elephant (12,000 lbs., 16 sq. in. foot)?

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PROBLEM The depths of the ocean can exceed 380 atm of pressure. How many pascals is this? How many psi?

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9.2 Factors That Affect the Properties of Gases

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Boyle’s Law

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Implications of Boyle’s Law

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Ideal Gases Any gas that behaves according to the predicted linear relationships. –Pressure/Volume –Volume/Temperature

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PROBLEM Given an ideal gas held at constant mass and temperature, what would be the volume of the gas if it was originally 125 ml, and its pressure is dropped from 1.40 atm to atm?

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Charles’s Law

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Implications of Charles’s Law

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Kelvin Scale So far we have measured temperature in degrees Celsius, a relative scale. Absolute temperature is measure in Kelvin (K, note no degree sign is used), this scale is related to the absolute motion of atoms. 0 K = °C Therefore Temp °C = Temp K

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PROBLEM Calculate the following temperatures in Kelvin. –Boiling Point of Water –Freezing Point of Water

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PROBLEM Given an ideal gas held at constant mass and pressure, what would be the temperature of the gas if it was originally at 125 °C, and its volume is dropped from 1.00 L to L?

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Combined Gas Law

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PROBLEM A sample of Hydrogen gas occupies 1.25 L at 80.0 °C and 2.75 atm. What would its volume be at 185 °C and 5.00 atm?

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Guy-Lussac and Avagadro Guy-Lussac’s Law stated that combined gases always reacted in small whole number ratios (sound familiar?) Avagadro hypothesized that the volume occupied by a gas is proportional to the number of gas particles and hence the moles of gas.

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Avagadro’s Hypothesis At a given pressure and temperature, equal volumes of gas contain equal numbers of moles. Standard Temperature and Pressure (STP) are defined as K and 1 atm, at which 1.00 mole of gas occupies L, defined as molar volume

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PROBLEM What volume would 1.00 mole of gas occupy at 37°C and 1.00 atm?

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9.3 The Ideal Gas Law

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Review of the Relationships

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Combine the Equations

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So What is the Value for R?

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PROBLEM Calculate the Ideal Gas Constant if pressure is measured in torr

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PROBLEM The volume of an oxygen cylinder is L. At a temperature of 32 °C the cylinder has a pressure of 945 torr. How many moles of Oxygen gas are in the cylinder?

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PROBLEM Given the amount of oxygen in the previous question, what is its mass? What is its density?

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Partial Pressures

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PROBLEM Given a L container at 45.00°C, what would be the total pressure in the container from a mixture of moles gaseous sulfur dioxide and moles hydrogen sulfide?

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9.5 Gases and Chemical Reactions

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The return of Stoichiometry You can use the gas laws to solve stoichiometry problems by converting values between states of matter.

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Example A sample of hydrogen gas has a volume of 8.00 L at a pressure of 5.00 atm and a temperature of 25 °C. What volume of gaseous water is produced in the following reaction at °C and atm, if all the hydrogen gas reacts with copper (II) oxide CuO(s) + H 2 (g) Cu(s) + H 2 O(g) ALGORITHM mol of Hydrogen (PV=nRT) mol of Water (formula) V of Water (PV=nRT)

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PROBLEM How many grams of calcium carbonate is formed if 3.45 L of carbon dioxide, measured at 45.0 C and 1.37 atm, react with excess CaO? CaO(s) + CO 2 (g) CaCO 3 (S)

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