# 1A10PPT - Chapter 10 Gases Gas Gas Model Gases are composed...

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Chapter 10 Gases

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Gas
Gas Model Gases are composed of tiny, widely-spaced particles. For a typical gas, the average distance between particles is about ten times their diameter.

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Gas Model (cont.) Because of the large distance between the particles, the volume occupied by the particles themselves is negligible (approximately zero). For a typical gas at room temperature and pressure, the gas particles themselves occupy about 0.1% of the total volume. The other 99.9% of the total volume is empty space. This is very different than for a liquid for which about 70% of the volume is occupied by particles.
Gas Model (cont.) The particles have rapid and continuous motion. For example, the average velocity of a helium atom, He, at room temperature is over 1000 m/s (or over 2000 mi/hr). The average velocity of the more massive nitrogen molecules, N 2 , at room temperature is about 500 m/s. Increased temperature means increased average velocity of the particles.

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The particles are constantly colliding with the walls of the container and with each other. Because of these collisions, the gas particles are constantly changing their direction of motion and their velocity. In a typical situation, a gas particle moves a very short distance between collisions. Oxygen, O 2 , molecules at normal temperatures and pressures move an average of 10 7 m between collisions. Gas Model (cont.)
There is no net loss of energy in the collisions. A collision between two particles may lead to each particle changing its velocity and thus its energy, but the increase in energy by one particle is balanced by an equal decrease in energy by the other particle. Gas Model (cont.)

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The particles are assumed to be point-masses, that is, particles that have a mass but occupy no volume. There are no attractive or repulsive forces at all between the particles. Ideal Gas
Gas Properties and their Units Pressure (P) = Force/Area units 1 atm = 101.325 kPa = 760 mmHg = 760 torr 1 bar = 100 kPa = 0.9869 atm = 750.1 mmHg Volume (V) unit usually liters (L) Temperature (T) ? K = --- ° C + 273.15 Number of gas particles expressed in moles (n)

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Gas Law Objectives For each of the following pairs of gas properties, (1) describe the relationship between them, (2) describe a simple system that could be used to demonstrate the relationship, and (3) explain the reason for the relationship. V and P when n and T are constant P and T when n and V are constant V and T when n and P are constant n and P when V and T are constant n and V when P and T are constant
Apparatus for Demonstrating Relationships Between Properties of Gases

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Decreased Volume Leads to Increased Pressure P α 1/V if n and T are constant
Relationship between P and V

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Boyle’s Law The pressure of an ideal gas is inversely proportional to the volume it occupies if the moles of gas and the temperature are constant.
Increased Temperature Leads to Increased Pressure P α T if n and V are constant

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Relationship between P and T
Gay-Lussac’s Law The pressure of an ideal gas is directly proportional to the Kelvin temperature of the gas if the volume and moles of gas are constant.

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V α T if n and P are constant Increased Temperature Leads to Increased Volume
Relationship between T and V

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## This note was uploaded on 03/03/2012 for the course CHEM 100 taught by Professor Mark during the Fall '06 term at Monterey Peninsula College.

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1A10PPT - Chapter 10 Gases Gas Gas Model Gases are composed...

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