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Chapter 9- The States of Matter u Gases indefinite volume and shape, low density. u Liquids definite volume, indefinite shape, and high density. u Solids definite volume and shape, high density u Solids and liquids have high densities because their molecules are close together.
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Kinetic Theory are evidence of this. uKinetic theory says that molecules are in constant motion. uPerfume molecules moving across the room
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Ê A Gas is composed of particles H usually molecules or atoms H Considered to be hard spheres far enough apart that we can ignore their volume. H Between the molecules is empty space. The Kinetic Theory of Gases Makes three assumptions about gases
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Ë The particles are in constant random motion. H Move in straight lines until they bounce off each other or the walls. Ì All collisions are perfectly elastic
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u The Average speed of an oxygen molecule is 1656 km/hr at 20ºC u The molecules don’t travel very far without hitting each other so they move in random directions.
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Kinetic Energy and Temperature u Temperature is a measure of the Average kinetic energy of the molecules of a substance. u Higher temperature faster molecules. u At absolute zero (0 K) all molecular motion would stop.
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Kinetic Energy % ofMolecules% ofMolecules High temp. Low temp.
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Kinetic Energy % ofMolecules% ofMolecules High temp. Low temp. Few molecules have very high kinetic energy
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Kinetic Energy % ofMolecules% ofMolecules High temp. Low temp. Average kinetic energies are temperatures
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u The average kinetic energy is directly proportional to the temperature in Kelvin u If you double the temperature (in Kelvin) you double the average kinetic energy. u If you change the temperature from 300 K to 600 K the kinetic energy doubles. Temperature
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u If you change the temperature from 300ºC to 600ºC the Kinetic energy doesn’t double. u 873 K is not twice 573 K
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Pressure u Pressure is the result of collisions of the molecules with the sides of a container. u A vacuum is completely empty space - it has no pressure. u Pressure is measured in units of atmospheres (atm). u It is measured with a device called a barometer.
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Barometer uAt one atmosphere pressure a column of mercury 760 mm high. Dish of Mercury Column of Mercury 1 atm Pressure
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Barometer uAt one atmosphere pressure a column of mercury 760 mm high. uA second unit of pressure is mm Hg u1 atm = 760 mm Hg 760 mm 1 atm Pressure
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Avagadro’s Hypothesis u Equal volumes of gas at the same temperature and pressure have equal numbers of molecules. u That means...
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Avagadro’s Hypothesis 2 Liters of Helium 2 Liters of Oxygen u Has the same number of particles as..
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u Only at STP 0ºC 1 atm u This way we compare gases at the same temperature and pressure. This is where we get the fact that 22.4 L =1 mole
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Think of it it terms of pressure. u The same pressure at the same temperature should require that there be the same number of particles. u The smaller particles must have a greater average speed to have the same kinetic energy.
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Liquids u Particles are in motion. u Attractive forces between molecules keep them close together. u These are called intermolecular forces. Inter = between Molecular = molecules
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Breaking intermolecular forces. u Vaporization - the change from a liquid to a gas below its boiling point. u Evaporation - vaporization of an uncontained liquid ( no lid on the bottle ).
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Evaporation u Molecules at the surface break away and become gas. u Only those with enough KE escape u Evaporation is a cooling process. u It requires heat. u Endothermic.
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Condensation / Change from gas to liquid / Achieves a dynamic equilibrium with vaporization in a closed system. / What is a closed system? / A closed system means matter can’t go in or out. (put a cork in it) What the heck is a “dynamic equilibrium? ”
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/ When first sealed the molecules gradually escape the surface of the liquid / As the molecules build up above the liquid some condense back to a liquid. Dynamic equilibrium
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/ As time goes by the rate of vaporization remains constant / but the rate of condensation increases because there are more molecules to condense. / Equilibrium is reached when Dynamic equilibrium
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Rate of Vaporization = Rate of Condensation / Molecules are constantly changing phase “Dynamic” The total amount of liquid and vapor remains constant “Equilibrium” Dynamic equilibrium
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Vaporization n Vaporization is an endothermic process - it requires heat. n Energy is required to overcome intermolecular forces n Responsible for cool earth. n Why we sweat. (Never let them see you.)
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Kinetic energy % of Molecules% of Molecules T1T1 Energy needed to overcome intermolecular forces
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Kinetic energy % of Molecules% of Molecules T2T2 u At higher temperature more molecules have enough energy u Higher vapor pressure.
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Boiling u A liquid boils when the vapor pressure = the external pressure u Normal Boiling point is the temperature a substance boils at 1 atm pressure. u The temperature of a liquid can never rise above it’s boiling point.
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Changing the Boiling Point u Lower the pressure (going up into the mountains). u Lower external pressure requires lower vapor pressure. u Lower vapor pressure means lower boiling point. u Food cooks slower.
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u Raise the external pressure (Use a pressure cooker). u Raises the vapor pressure needed. u Raises the boiling point. u Food cooks faster. Changing the Boiling Point
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Solids u Intermolecular forces are strong u Can only vibrate and revolve in place. u Particles are locked in place - don’t flow. u Melting point is the temperature where a solid turns into a liquid.
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u The melting point is the same as the freezing point. u When heated the particles vibrate more rapidly until they shake themselves free of each other. u Ionic solids have strong intermolecular forces so a high mp. u Molecular solids have weak intermolecular forces so a low mp.
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Crystals u A regular repeating three dimensional arrangement of atoms in a solid. u Most solids are crystals. u Amorphous solids lack an orderly internal structure. u Think of them as supercooled liquids.
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Cubic
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Body-Centered Cubic
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Face-Centered Cubic
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Phase Changes Solid Liquid Gas Melting Vaporization CondensationFreezing
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Liquid Sublimation Melting Vaporization Condensation Solid Freezing Gas
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Energy and Phase Change u Heat of vaporization energy required to change one gram of a substance from liquid to gas. u Heat of condensation energy released when one gram of a substance changes from gas to liquid. u For water 540 cal/g
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Energy and Phase Change u Heat of fusion energy required to change one gram of a substance from solid to liquid. u Heat of solidification energy released when one gram of a substance changes from liquid to solid. u For water 80 cal/g
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Water and Ice Ice Water and Steam Steam -20 0 20 40 60 80 100 120 0 40120 220760800 Heating Curve for Water
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Water and Ice Ice Water and Steam Steam -20 0 20 40 60 80 100 120 0 40120 220760800 Heating Curve for Water Heat of Vaporization
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Water and Ice Ice Water and Steam Steam -20 0 20 40 60 80 100 120 0 40120 220760800 Heating Curve for Water Heat of Fusion
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Water and Ice Ice Water and Steam Steam -20 0 20 40 60 80 100 120 0 40120 220760800 Heating Curve for Water Slope = Specific Heat Steam Water Ice
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Water and Ice Ice Water and Steam Steam -20 0 20 40 60 80 100 120 0 40120 220760800 Heating Curve for Water Both Water and Steam
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Water and Ice Ice Water and Steam Steam -20 0 20 40 60 80 100 120 0 40120 220760800 Heating Curve for Water Ice and Water
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Water and Ice Ice Water and Steam Steam -20 0 20 40 60 80 100 120 0 40120 220760800 Heating Curve for Water
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Calcualting Energy u Three equations Heat = specific heat x mass x T u Heat = heat of fusion x mass u Heat = heat of vaporization x mass
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Numbers to Know For ice S.H. = 0.50 cal/g C For water S.H = 1 cal/g C For steam S.H. = 0.50 cal/g C u Heat of vaporization= 540 u Heat of fusion = 80 cal/g
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How to do it u The total heat = the sum of all the heats you have to use u Go in order Heat Ice Below 0 C + Melt Ice At 0 C + Heat Water 0 C - 100 C + Boil Water At 100 C + Heat Steam Above 100 C
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Examples How much heat does it take to heat 12 g of ice at -6 C to 25 C water? How much heat does it take to heat 35 g of ice at 0 C to steam at 150 C?
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