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chapter 13 chemistry
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Chapter 13- States of Matter Gases Kinetic Molecular Theory · Model to describe properties of gases · Kinetic=move · Theory describes behavior in terms of particles in motion · Model makes assumptions about size, motion, and energy of gas particles Particle size · Gases consist of small particles that are separated from one another by empty space · Because gas particles are far apart, there are no significant attractive or repulsive forces among them Particle Motion · Gas particles are in constant random motion collide with other particles or with the walls of their container · Have elastic collisions-no kinetic energy is lost · Kinetic energy can be transferred between colliding particles, but the total kinetic energy of the 2 particles don’t change Particle energy · 2 factors determine the kinetic energy of a particle · Mass, velocity KE=1/2mv2 · In a sample of a dingle gas all particles have the same mass but all particles do not have the same velocity · Because of this particles do not have the same kinetic energy · Kinetic energy and temperature are related · Temperature- a measure of the average kinetic energy of the particles of matter · At a given temperature, all gases have the same average kinetic energy Explaining the behavior of Gases Low Density · Theory states- great deal of space exists between gas particles · The rest are fewer chlorine molecules than gold atoms in the same volume Cl=solid Au=gold Diffusion & Effusion Theory states-no force of attraction between gas particles · Gas particles can move easily past each other · The space into which a gas flows is already occupied by another gas · This random motion causes gases to mix until they are evenly distributed · Diffusion- Movement of one material through another · Move from high concentration to low concentration · The rate of diffusion depends on the mass of the particles · For lighter particles to have the same average kinetic energy as heavier particles, they must have a greater velocity (KE=1/2mv2 · Effusion is process related to diffusion · Graham’s Law of Effusion- States that the rate of effusion for a gas is inversely proportional to the square root of the molar mass (GFM) · This law applies to rates of diffusion · Using this law you can setup a proportion to compare the diffusion rates for 2 gases Formula: Gas pressure · Pressure-defined as force per unit area · Gas particles exert pressure when they collide with the walls of their container Atmospheric pressure · Because the particles in air move in every direction, they exert pressure in all directions Measuring Air pressure · Barometer-instrument used to measure atmospheric pressure · Height of the Hg in the tube is determined by 2 forces · Gravity pushing down on Hg; Humidity/temperature causes air pressure to change · An increase in air pressure causes Hg to rise, a decrease it falls · Monometer-instrument used to measure gas pressure in a closed container · Flask in connected to a U-tube containing Hg · Before the gas is released Hg is at the same height in arms · After the gas is released the height in the 2 arms are no longer equal · If gas pressure > atmospheric pressure the liquid on the left decreases and the liquid on the left increases Pgas=Patm+Phg · If gas pressure < atmospheric pressure the liquid on left increases and liquid on right decreases Pgas=Patm-PHg Units of Pressure Pascal (Pa)-Si unit of pressure 1Pa=1N/M2 Other units: mmHg, torr, atmosphere (atm), psi, kilopascal (kPal) 1.00atm=760 torr=101.3 kPa=14.7 psi (at 0* C) Dalton’s Law of Partial Pressure · Law states that the total pressure of a mixture of gases is equal to the sum of the pressures of all the gases in the mixture · Partial pressure depends on: Number of moles of gas, size of the container, temperature of mixture · It doesn’t depend on the identity of the gas Patm= p1 + p2 + p3….
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