Thursday, January 7, 2021

Chapter 13 chemistry

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Chapter 1- States of Matter


Gases


Kinetic Molecular Theory


· Model to describe properties of gases


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· 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 particles don't change


Particle energy


· factors determine the kinetic energy of a particle


· Mass, velocity KE=1/mv


· 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/mv


· 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 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 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 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/M


Other units mmHg, torr, atmosphere (atm), psi, kilopascal (kPal)


1.00atm=760 torr=101. 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 + p + p….


· When gases are made in a lab they are made over water, so the gas is saturated with water


· Pgas=Ptotal-Pwater


· Water pressure will be given to you Practice problems on pg 4-6


· Water pressure will be given to you.


Forces of attraction


· Intramolecular force-Force within atoms, ions, molecules (bonding)


· Ex dispersion, H-bonds


· Intermolecular force-force between atoms, ions, or molecules


· Ex dispersion, H-bonds


Dispersion force


· Weak forces that result from temporary shift of electrons in the electron cloud


· Occurs when non polar molecules are in close contact or collide


· Electrons in the cloud repel each other causing the electrons to have a higher density in one region of each cloud


· Forms temporary dipole; When the dipoles are close together a weak dispersion force exists; Occurs in identical non polar molecules


Dipole-Dipole forces


· Attractions between oppositely charged regions of polar molecules


· Contain permanent dipoles


· Neighboring polar molecules orient themselves so that charged regions line up.


· Forces are usually stronger than dispersion forces


· Pg 4-5 pictures of bonds


Hydrogen bonds


· A dipole-dipole attraction that occurs between molecules containing a hydrogen atom bonded to a small electronegative atom with at least one lone electron pair


· Hydrogen must be bonded to Fluorine, Oxygen, Nitrogen


· H has a positive charge, O has a negative charge so that one molecule is attracted to the O in another molecule


Liquids


Kinetic Molecular Model


· Have a constant motion


· No foxed position so they take the shape of a container


· Force of attraction is greater than in gases so liquids have a fixed volume


Density & Compression


· At 5C and 1atm, liquids are closer than gases because of their greater intermolecular forces holding them together


· Like gases, liquids can be compressed, but only by a small volume because the molecules are relatively close together


Fluidity


· Ability to flow


· Liquids can diffuse through other liquids but at a slower rate than gases because of intermolecular forces


· Liquids are less fluid than gases


Viscosity


· Is the measure of the resistance of a liquid to flow


· The attractive force slows their movement


· Viscosity is determined by the type of intermolecular forces, shape of the particle, and temperature


· Warm-faster flow, cooler- slow flow larger/longer-slow small/short-fast


Surface tension


· Particles in the middle of a liquid can be attracted to particles all around them


· Particles at the surface have no attractive force from above to balance the attraction for below; so there is a greater force pulling down on particles at the surface


· Surface tension- energy required to increase the surface area of a liquid by a given amount


· Generally the stronger the attraction between particles the greater the surface tension


· Water has a high surface tension because it can form multiple hydrogen bonds


· Surfactants- compound that lower the surface tension of water (break hydrogen bonds)


Capillary action


· A narrow container; surface of water forms a meniscus forces cause this


· Cohesion- force of attraction between identical molecules


· Adhesion- force of attraction between different molecules


· The adhesive force between the water and glass is greater than the cohesive force between the water; so water rises along the inner walls of the cylinder


Kinetic molecular theory


· Are in constant motion


· Have a strong attractive force between particles, this limits the motion, causing more order


· Because this solids have a definite shape and volume are much less fluid


Density of solids


· Particles are packed closely together so they are more dense


· Because most solids sink, except water has fewer particles in given volume


Crystalline solids


· Solid where atoms, ions, or molecules are arranged in a orderly, geometric shape


· Unit cell- smallest arrangement of connected points that can be repeated in 1 direction to form a lattice


· Shape of a crystal is determined by the type of unit cell


· 7 different crystals on pg 401


· Crystalline solids can be classified into 5 groups based on the type of particles they contain


· Pg 40 table 1-4


· Amorphous solids- particles are not arranged in a regular repeating pattern


· Forms when the motion material cools too quickly and the crystals don't have time to form


Phase changes


MeltingÞsolidÞliquid


· Solids well absorb heat energy and break the bonds that are holding them together


· Temperature does not change as the solid is melting


· Amount of energy needed depends on the strength of that bond


· Melting point- temperature at which the liquid phase and solid phase of a given substance can coexist


Vaporization liquidÞgas


· Once all ice melts the addition of energy increases the kinetic energy of the liquid and the temperature increases


· Evaporation- when vaporization occurs only at the surface of a liquid


· Liquid molecules must absorb energy, break forces of attraction, and enter gas phase ex sweat


· In a closed container water collects above that liquid and exerts pressure on the surface of the liquid called vapor pressure


· Boiling point- temperature at which vapor pressure of a liquid equals the external or atmospheric pressure


Sublimation solidÞgas


· Ex solid iodine, solid carbon dioxide, mothballs, air freshener


· Absorb energy


Condensation gasÞliquid


· Loses energy, velocity decreases when molecules collide they are more likely to form bonds or increase the force of attraction, and changes to the liquid phase


· Reverse vaporization


Deposition gasÞsolid


· Reverse of sublimation energy is released ex frost & snow


Freezing liquidÞsolid


· Energy is lost, velocity decreases bonds form and hold the molecules in a fixed position


· Reverse of melting


· Freezing point- temperature at which a liquid is converted in to a solid


· Is equal to the melting point


Phase diagrams


· Graph of pressure vs. temperature that shown in which phase a substance exists


· Under different conditions of temperature and pressure


· curves separate the regions from one another solid, liquid gas


· On the curve phases of matter exist


· Triple point-temperature at which 6 phase changes can occur and phases of matter can exist


· Critical point- indicates the critical temperature and pressure above which a substance cannot exist as a liquid


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