States of Matter 9.2

Ch. 9 Heat and States of MatterA. Kinetic Molecular TheoryKinetic Theory of MatterTiny, constantly moving particles make up all matter.TemperatureA measure of the average kinetic energy of particles in matterThe kinetic energy (motion) of these particles increases as temperature increases.TemperatureSI unit?Subtract 273 from a temperature in Kelvin to convert to degrees Celsius.

Temperature is a measure of molecular movement.0 Kelvin is NO movement. Absolute zero.

Thermal EnergyThe sum of the kinetic and potential energies of all the particles in an objectPotential energy: stored energy of an object due to its position.

Molecules and atoms have attractive electric forces on each other. As they move farther apart, the have more potential energy.4

Thermal EnergyDoes the ball rolling have more/less/same thermal energy as the stationary ball?

No. It has more kinetic energy but not more thermal energy.5HeatIs thermal energy that flows from something at a higher temperature to something at a lower temperature.

Specific HeatThe amount of thermal energy needed to raise the temperature of 1 kg of a material 1 degree Celsius.Which heats up faster? The land or water?

Specific HeatWhich heats up faster? The land or water?C water = 4184 J / kg CC sand = 664 J / kg C

for equal amounts of sand/water, requires about 6x the thermal energyThermal Energy EquationThe thermal energy of an object changes as its temperature changesChange in thermal energy (Q) = JMass (m) = kgChange in temperature (T) = CSpecific heat (C) = J/kg CQ = m(Tf Ti) CProblemThe air in a living room has a mass of 72 kg and a specific heat of 1,010 J/kg C. What is the change in thermal energy when the air warms from 20 to 25C?

Given:m = 72 kgC = 1010 J/kg CTf Ti = 25 20 = 5CQ = ?Equation:Q = m(Tf Ti) CQ = (72 kg) (25-20 C) (1010 J/kg C) Q = 363,600 J (joules)Measuring Specific HeatA calorimeter is used to help measure the specific heat of a substance.Mass the sampleInitial temperature of water in calorimeterMaterial added to inner chamberAs cools, thermal energy transferred to water and temp of water increasesInitial and final temps of water are known.Energy absorbed by water can be calculated by temp change of fixed massThermal energy released = absorbedCan calculate specific heat

Q = m(Tf Ti) CMeasuring Specific HeatWaterMass = 100 g or 0.1 kgChange in temp = ?Cwater = 4,184 J/kg CCAN SOLVE FOR Q! Energy in = Energy outCalcium ChlorideMass = 6 g or 0.006 kgChange in temp = sameQ = sameSolve for C (specific heat!)

Q = m(Tf Ti) CStates of Matter 9.2Four States of MatterThere are four states of matter created by the differences in the attraction between particles.

Solid StateLow KE, particles vibrate but cant move around.Because of strong attraction between particles, solids have a fixed volume and shape.

Liquid StateHigher KE particles can move around but are still close together.Indefinite shape takes the shape of the containerDefinite volume

Gas StateHigh KE particles can separate and move throughout container.Particles are much farther apart and attractive forces are weak so particles no longer cling together. Indefinite shape and volume; Spread evenly in container through diffusion

Plasma StateVery high KE particles collide with enough energy to break into charged particles (+/-)Gas-like, indefinite shape and volumeStars, fluorescent light bulbs, TV tubes contain plasmasMost common state of matter in universe.

LinkConsists of positively and negatively charged particles.High speed collisions knock electrons from atoms.

18Phase ChangesChanges in the thermal energy of a material can cause it to change from one state to another.

MeltingSolid to liquidFreezingLiquid to solid

Melting point = freezing pointChanging States - MeltingAs temperature increases, particles move faster and attractive force cant keep them in place.Temperature at which a solid begins to melt is its melting point.

Changing States - MeltingThe amount of energy required to change 1 kg of a substance from a solid to a liquid at its melting point is the heat of fusion.

Changing States - FreezingLowering temperature of a liquid decreases the particles average KE and they move slower. Attractive forces are strong enough to create an ordered arrangement.The heat of fusion is also the energy released when a liquid freezes.

Phase ChangesVaporization (boiling)Liquid to gas at the boiling pointEvaporationLiquid to gas below the boiling pointCondensationGas to liquidChanging States - VaporizationLiquid to gas at the boiling pointAs temperature of a liquid increases, the particles move faster and farther apart. The forces between them become so weak that the particles no longer cling together.

Changing States - VaporizationVaporization at the surface of a liquid is called evaporation. Evaporation causes the temperature of the liquid to decrease.Vaporization that occurs within the liquid is called boiling.

Changing States - VaporizationThe boiling point is the temperature at which the pressure of the vapor in the liquid equals the pressure acting on its surface.The heat of vaporization is the amount of energy required for 1 kg of liquid at its boiling point to become a gas.

Changing States - CondensationCondensation when a gas changes to a liquidThe heat of vaporization is also the amount of energy released during condensation.

Heating Curve of a SubstanceKinetic EnergyMotion of particlesRelated to temperature

Potential EnergySpace between particlesRelated to phase changes

videoHeating Curves

Heat of vaporizationHeat of fusionThermal ExpansionMost matter expands when heated and contracts when cooled. Temp causes KE. Particles collide with more force & spread out.An expansion joint allows concrete to expand and contract without damage.Thermometers?Drawers and cabinets?Water?

Chapter 9 section 3Ways to Transfer Thermal EnergyConductionConvectionRadiation

DefinitionsTransfer of thermal energy between colliding particles is ______________Transfer of thermal energy in a fluid by the movement of the fluid from place to place is _______________.Transfer of thermal energy by electromagnetic waves: ______________.

conductionconvectionradiationIdentify

Thermal ConductorsThermal energy can be transferred by conduction in ALL materialsThe rate at which thermal energy is transferred VARIES by materialMaterials that transfer thermal energy easily are called thermal conductorsSolids and liquids are faster conductors than gases (solid > liquid > gas) WHY?Best thermal conductors are metals

Convection CurrentsConvection: transfer of thermal energy in a fluid by the movement of the fluid from place to placeConvection Currents: Warmer fluids have a different density than a cooler fluidMore dense cooler fluid sinks, pushing up warmer fluidsRising and sinking of fluid creates a convection current.Thermal energy transferred by movement of fluid from place to place.

Convection CurrentsDeserts and RainforestsWhere is air warmer?Surface or higher altitudes?Equator or poles?

Why do we have rainforestsat the equator?Dry air carried farther north& south creating a zone of deserts!

Hot, moist air rises, cools, water condenses and falls back as rain.37Radiation and Radiant EnergyRadiation: transfer of energy by electromagnetic waves.When radiation strikes, some energy is absorbed, some transferred through the material, and some is reflected. How much does what?Depends on the material

Sand, grass, car color38Thermal InsulatorsA material in which thermal energy moves slowlyGases are usually better insulators than solids or liquidsGood conductors are poor thermal insulators.

Section 4Using Thermal EnergyLit a Camp fireHeated a houseMowed the lawnDriven in a carBoiled waterHeating Systems: Forced Air

Most common. Fuel burned in furnace, fan blows heated air through ducts which lead to vents. Cool air returns and is reheated.41Heating Systems: Radiator

Closed metal container with hot water or steam. Heat transferred to air surrounding radiator via conduction. Warm air moves in room by convection42Heating System: Electric

Converts electrical energy to thermal. Electrically heated coils heats surrounding air by conduction and convection. Not as widely used. If walls too thin for forced air systems (ducts), may be only practical method.43ThermodynamicsThe study of the relationship between thermal energy, heat and work.How else can you increase the thermal energy of an object besides heating it?

A system is anything you can draw a boundary aroundYou can do work and rub hands together creating friction! Hands considered a system. A group of objects such as a cars engine or a ball.44First Law of ThermodynamicsEnergy is conserved (cannot be created or destroyed)The increase in thermal energy of a system equals the work done on the system plus the heat added to the system.Open system: thermal energy flows across the boundary or work is done across the boundary of the system. Energy of an open system can changeClosed system: No outside work is done or thermal energy flows across boundary. The total energy of the system doesnt change.

Heat flow hot to coldIncrease of TE of colder object = decrease in TE of warmer objectEnergy is not created or destroyed (1st law satisfied)

Second Law of ThermodynamicsIt is impossible for heat to flow from a cooler object to a warmer object unless work is done.Entropy in a closed system never decreases

Converting Thermal Energy to WorkHeat Engine: a device that converts TE into work. i.e. a carSome energy is always transferred to the surroundings.Internal combustion engine fuel is burned in the engine in chambers or cylinders. Pistons move up and down in the cylinder in four separate strokes. Intake, Compression, Power and Exhaustpage 275.RefrigeratorsHow do refrigerators stay cold? How can thermal energy be moved from a cold area to a warmer area?

Coolant pumped through pipes. Evaporates at low temperature. Pumped through expansion valve and changes to a gas (cools) cold gas pumped through pipes in refrigerator. Absorbs thermal energy inside refrigerator and inside refrigerator cools. Gas then pumped to a compressor. Compressed gas now warmer than room. Gives off thermal energy as it cools and changes to a liquid.49EntropyA measure of how spread out or dispersed energy is. (randomness or disorder of a system)Entropy increases when energy becomes more spread out. (less concentrated)All events that occur cause the entropy of the universe to increase. (Entropy always increases)

As energy spreads out it becomes less usable.