Chemistry Unit 2 States of Matter and Specific Heat

States of Matter 1. SOLID Definite volume Definite shape Usually hard because molecules are packed together Particles have little movement, but do vibrate against one another Can be made of crystals in a pattern called a crystal lattice --repeating, 3D pattern --Ex. Diamonds Can form allotropes --Two or more different molecular forms of the same element --Ex. carbon: diamond and graphite Amorphous solids --Solids which lack crystals --disordered arrangement of their component particles --Ex. plastic, asphalt, wax, glass

States of Matter 1. SOLIDS continued Very difficult to compress 2. LIQUID Definite volume No definite shape Can flow (viscosity--resistance to flow) Particles slide past one another Less dense than solids More compressible than solid but less compressible than gas solid liquid

States of Matter 3. GAS No definite volume No definite shape Particles move very rapidly Lower densities than solids and liquids because particles are farther apart Can be compressed because a lot of space between the particles Expanded when heated gas

States of Matter 4. PLASMA Gaseous mixture of electrons and positive ions Behaves like a gas because no definite shape nor volume Temperature must be between 50,000 K and 100,000,000 K True Plasma--high temperatures that charge up the atoms naturally (not found on Earth) --Ex. stars, sun Partial Plasma--can exist on Earth --electricity acts as special energy that charges up the gas --Ex. neon lights, lightning bolts, Aurora Borealis

Phase Changes (changes in state of matter) 1. MELTING: solid to liquid heat goes into the solid as it melts NO temperature change during phase changes! Pure solids melt at definite temperatures Melting point (MP): temperature at which a solid turns into a liquid --Can change is substance is NOT pure Heat of Fusion: energy required to melt a substance 2. FREEZING: liquid to solid heat leaves the liquid as it freezes NO temperature changes during phase changes! Objects freeze at same point they melt --Can change is substance is NOT pure Same amount of energy needed to melt is needed to freeze, therefore same heat of fusion

Phase Changes (changes in state of matter) 3. VAPORIZATION: liquid to gas heat goes into the liquid as it vaporizes NO temperature change during phase changes! Includes both boiling and evaporation --Boiling: bubbles form at bottom of a liquid and rise to the top -Can only take place at certain temperatures and pressure Normal Boiling Point: temperature at which vapor pressure is equal to the standard atmospheric pressure (1 atm) --STP: standard temperature and pressure -Standard temperature = 0oC or 273 K -Standard pressure = 1 atm or kPa or 760 mmHg or 760 torr

Phase Changes (changes in state of matter) 3. VAPORIZATION: continued --Vapor Pressure--pressure exerted by the molecules of a confined vapor Boiling Point: temperature at which vapor pressure equals atmospheric pressure Evaporation: occurs at the surface of a liquid at any temperature as molecules or atoms escape from the liquid and turn into a vapor --Not all molecules have the same energy --Temperature is the measure of average kinetic energy --Liquids contain Weak Attractive Forces (WAFs) that keep the molecules stuck together --If KE>WAFs then escape to vapor --If KE<WAFs then stays a liquid --Evaporation removes heat from the environment, a cooling process

Phase Changes (changes in state of matter) 3. VAPORIZATION: continued Heat of Vaporization: energy required to evaporate a liquid 4. CONDENSATION: gas to liquid heat leaves the gas as it condenses NO temperature change during phase changes! Gases are very excited atoms, when lose energy they slow down and begin to collect Condenses at same temperature and pressure that it vaporized Requires the same amount of energy as it did to vaporize, therefore same heat of vaporization

Phase Changes (changes in state of matter) 5. SUBLIMATION: solid to gas heat goes into the solid as it sublimes NO temperature change during phase changes! Doesn't go through liquid phase Ex.: solid CO2, iodine crystals, camphor (moth balls) 6. DEPOSITION: gas to solid heat leaves the gas to form a solid NO temperature change during phase changes! Ex.: frost

Phase Changes (changes in state of matter) Dynamic Equilibrium: rate of one phase change equals the rate of its opposite phase change Triple Point: the temperature and pressure where all 3 states of matter exist at the same time

Place the words in the correct locations on the graph. solid liquid gas melting freezing vaporization condensation melting point boiling point

Place the words in the correct locations on the graph. solid liquid gas melting freezing vaporization condensation sublimation deposition triple point

Kinetic Molecular Theory (KMT) All substances are made of atoms or molecules that are in constant state of motion Four Basic Assumptions 1. A gas is made of particles, either molecules or atoms. 2. Gas molecules are in constant random motion. --move in straight line unless it collides with something 3. All collisions are perfectly elastic. --Elastic Collision: no net energy loss due to friction 4. Average KE of a molecule of gas is directly proportional to the Kelvin temperature of the gas.

Kinetic Energy and Temperature Kinetic Energy: energy of motion; KE =1/2mv2 Average KE of particles is directly proportional to its temperature in Kelvin No theoretical upper limit to temperature. There is a lower limit to temperature --Absolute Zero: temperature at which all motion stops --lowest possible temperature --0 K or -273oC Kelvin scale is a direct measure of the average KE K = oC + 273

Kinetic Energy and Pressure Pressure: measure of the force exerted on a unit area Gas Pressure: result of simultaneous collisions of many gas particles on an object Atmosphere of Pressure (ATM): results from the collisions of air molecules with objects on earth --occurs because gravity holds air molecules close to Earth --atmospheric pressure decreases with altitudes --Barometer: used to measure atmospheric pressure Units of Pressure 1 atm = kPa = 760 mmHg = 760 torr --SI unit is pascal (Pa) STP = 273 K and 1 atm

Conversion Problems 1) 55 oC = 328 K5) 375 mmHg = 0.49 atm 2) - 63 oC = 210 K 6) 2.7 atm = kPa 3) -82 oC = 191 K7) 890 torr = kPa 4) 179 oC = 452 K8) 0.98 atm = mmHg

Specific Heat Heat: energy that moves from hot to cold --measured in joules (J) or calories (cal) J = 1 cal Temperature: measure of average kinetic energy Specific Heat: amount of heat energy needed to change 1 gram of substance by 1oC --is positive if temperature increases --is negative if temperature decreases --specific heat of water is J/goC --Calorimeter: device used to measure heat energy

Q = m c T Q: heat energy (J)c: specific heat (J/goC) m: mass (g) T: change in temperature final - initial