1 States of Matter Ch.13

2 Review: Solids, Liquids, and Gases A. Solid A. Solid 1. Definite shape 1. Definite shape 2. Definite volume 2. Definite volume 3. Molecules vibrate in place and are close together 3. Molecules vibrate in place and are close together B. Liquid 1. No definite shape 1. No definite shape 2. Definite volume 2. Definite volume 3. Molecules move a little more and are further apart 3. Molecules move a little more and are further apart C. Gas 1. No definite shape 1. No definite shape 2. No definite volume 2. No definite volume 3. Molecules move freely and are far apart 3. Molecules move freely and are far apart

3 Kinetic Theory Kinetic energy – the energy an object has because of its motion Kinetic energy – the energy an object has because of its motion –Faster object moves more kinetic energy Kinetic Theory – all matter consists of tiny particles that are in constant motion Kinetic Theory – all matter consists of tiny particles that are in constant motion

4 Kinetic theory of gases Three assumptions of the kinetic theory as it applies to gases Three assumptions of the kinetic theory as it applies to gases 1. Particles in a gas are considered to be small, hard spheres with an insignificant volume Particles are not attracted to one anotherParticles are not attracted to one another 2. Motion of the particles in a gas is rapid, constant, and random –Oxygen molecules at 20 °C move at 1700 km/h 3. All collisions between particles in a gas are perfectly elastic Elastic collision – when kinetic energy is transferred without loss from one particle to anotherElastic collision – when kinetic energy is transferred without loss from one particle to another

5 If molecules move so fast why don’t we smell odors immediately? 1700 km/h means the odor from a hot pizza in Washington D.C. should reach Mexico City in 115 mins km/h means the odor from a hot pizza in Washington D.C. should reach Mexico City in 115 mins. Does this really happen? Does this really happen? –No, Why? –Molecules responsible for odor are constantly striking molecules in air and rebounding in other directions.

6 Gas pressure Gas pressure – results from the force exerted by a gas per unit surface area of an object. Gas pressure – results from the force exerted by a gas per unit surface area of an object. Gas pressure is the result of simultaneous collisions of billions of rapidly moving particles in a gas with an object Gas pressure is the result of simultaneous collisions of billions of rapidly moving particles in a gas with an object Units: Pascal (Pa), atmospheres (atm), or mm Hg Units: Pascal (Pa), atmospheres (atm), or mm Hg 1 atm = 760 mm Hg = kPa 1 atm = 760 mm Hg = kPa

7 Terms Atmospheric pressure – results from the collisions of atoms and molecules in air with objects Atmospheric pressure – results from the collisions of atoms and molecules in air with objects Vacuum – empty space with no particles and no pressure Vacuum – empty space with no particles and no pressure Barometer – device that is used to measure atmospheric pressure Barometer – device that is used to measure atmospheric pressure Standard atmosphere – pressure required to support 760 mm Hg in a mercury barometer at 25 °C Standard atmosphere – pressure required to support 760 mm Hg in a mercury barometer at 25 °C

8 Kinetic energy and temperature As a substance is heated, some energy is stored with the particles. As a substance is heated, some energy is stored with the particles. –Called potential energy –Does not raise temperature of substance Remaining energy speeds up the particles Remaining energy speeds up the particles –Increases kinetic energy –Increases temperature An increase in average kinetic energy of particles causes the temperature to increase. An increase in average kinetic energy of particles causes the temperature to increase. At absolute zero (O K) particles theoretically stop moving At absolute zero (O K) particles theoretically stop moving

9 Kelvin Reminder: K = °C +273 Reminder: K = °C +273 Kelvin temperature scale reflects the relationship between temperature and average kinetic energy Kelvin temperature scale reflects the relationship between temperature and average kinetic energy –It is directly proportional –Ex. Particles in a gas at 200 K have twice the amount of kinetic energy as particles at 100 K

10 Differences between gas and liquids According to kinetic theory According to kinetic theory –In gases no attraction between particles –In liquids particles are attracted to each other This attraction keep the particles in a liquid close together, which is why liquids have a definite volume This attraction keep the particles in a liquid close together, which is why liquids have a definite volume Attraction also reduces the amount of space between the particles in liquid  liquids are denser than gases Attraction also reduces the amount of space between the particles in liquid  liquids are denser than gases

11 Evaporation Vaporization – conversion of a liquid to a gas or vapor Vaporization – conversion of a liquid to a gas or vapor Evaporation – when such a conversion occurs at the surface of a liquid that is not boiling Evaporation – when such a conversion occurs at the surface of a liquid that is not boiling During evaporation, only those molecules with a certain minimum kinetic energy can escape from the surface of the liquid. During evaporation, only those molecules with a certain minimum kinetic energy can escape from the surface of the liquid.

12 Have you ever experienced evaporative cooling? Of course you did Of course you did –Every time you perspire When you perspire, water molecules in your sweat absorb heat from your body and evaporate from your skin’s surface When you perspire, water molecules in your sweat absorb heat from your body and evaporate from your skin’s surface Perspiration that remains cools you further by absorbing more body heat Perspiration that remains cools you further by absorbing more body heat

13 Vapor Pressure Vapor pressure – measure of the force exerted by a gas above a liquid Vapor pressure – measure of the force exerted by a gas above a liquid In a system at constant vapor pressure, a dynamic equilibrium exists because the rate of evaporation of liquid equals the rate of condensation of vapor. In a system at constant vapor pressure, a dynamic equilibrium exists because the rate of evaporation of liquid equals the rate of condensation of vapor. Vapor pressure  as temperature  Vapor pressure  as temperature  –Kinetic energy  Vapor pressure data indicates how volatile a liquid is or how easily it evaporates. Vapor pressure data indicates how volatile a liquid is or how easily it evaporates. Can be measured with a manometer Can be measured with a manometer

14 Boiling point Rate of evaporation of a liquid from an open container increases as the liquid is heated Rate of evaporation of a liquid from an open container increases as the liquid is heated When a liquid is heated to a temperature at which particles throughout the liquid have enough kinetic energy to vaporize, the liquid begins to boil When a liquid is heated to a temperature at which particles throughout the liquid have enough kinetic energy to vaporize, the liquid begins to boil Temperature at which the vapor pressure of the liquid is just equal to the external pressure on the liquid is the boiling point Temperature at which the vapor pressure of the liquid is just equal to the external pressure on the liquid is the boiling point

15 Boiling point and pressure changes Liquids don’t always boil at the same temperature Liquids don’t always boil at the same temperature Boiling occurs when the vapor pressure equals the external pressure Boiling occurs when the vapor pressure equals the external pressure Atmospheric pressure is lower at higher altitudes Atmospheric pressure is lower at higher altitudes –So at higher altitudes water will boil at lower temperatures –So it will take longer to cook pasta on top of a mountain

16 How does a pressure cooker work? In a pressure cooker, the vapor cannot escape so the vapor pressure increases. In a pressure cooker, the vapor cannot escape so the vapor pressure increases. –  water boils at temperatures above 100 °C –Food cooks quicker.

17 Summary Lower external pressure = lower boiling point Lower external pressure = lower boiling point Why Why –Particles in the liquid need less kinetic energy to escape from the liquid Higher external pressure = higher boiling point Higher external pressure = higher boiling point Why Why –Particles in the liquid need more kinetic energy to escape from the liquid

18 Boiling Temperature of boiling water can never be increased Temperature of boiling water can never be increased While water is boiling the temperature remains constant While water is boiling the temperature remains constant If you add more heat energy just increase rate of boiling not temperature If you add more heat energy just increase rate of boiling not temperature Normal boiling point – boiling point of a liquid at a pressure of 101.3kPa Normal boiling point – boiling point of a liquid at a pressure of 101.3kPa –What is the normal boiling point of water

19 Solids General properties of solids reflect the orderly arrangement of their particles and the fixed locations of their particles. General properties of solids reflect the orderly arrangement of their particles and the fixed locations of their particles. Solids are Solids are –Dense –Not easily compressed –Do not flow

20 Melting point When a solid is heated When a solid is heated –Particles vibrate more –Kinetic energy increases –Solid eventually breaks down and melts Melting point – temperature at which a solid changes into a liquid Melting point – temperature at which a solid changes into a liquid Melting and freezing point are at the same temperature Melting and freezing point are at the same temperature –Liquid and solid phase are in equilibrium

21 Crystal structure and unit cells Crystal lattice – particles are arranged in an orderly, repeating, and 3-D pattern Crystal lattice – particles are arranged in an orderly, repeating, and 3-D pattern Shape of a crystal reflects the arrangement of the particles within the solid Shape of a crystal reflects the arrangement of the particles within the solid Type of bonding in a crystal determines it melting point Type of bonding in a crystal determines it melting point In general In general –Ionic solids have high melting points –Covalent solids have low melting points Not all solids melts some decompose Not all solids melts some decompose –Ex. Wood Unit cell – smallest group of particles within a crystal that retains the geometric shape of the crystal Unit cell – smallest group of particles within a crystal that retains the geometric shape of the crystal

22 Non-crystalline solids Not all solids are crystalline; some are amorphous Not all solids are crystalline; some are amorphous Amorphous solid – lacks an ordered internal structure Amorphous solid – lacks an ordered internal structure Ex: glass, rubber, plastic, and asphalt Ex: glass, rubber, plastic, and asphalt Atoms are randomly arranged Atoms are randomly arranged Glass- transparent fusion product of inorganic substances that have cooled to a rigid state without crystallizing. Glass- transparent fusion product of inorganic substances that have cooled to a rigid state without crystallizing. –Glass sometimes called supercooled liquids

23 Changes of state of water