Kinetic Energy & Changes of State

Kinetic Energy & Changes of StateChapter 10 Section 2Page 348

Temperature & Kinetic EnergyThe energy of moving objects is Kinetic Energy

The temperature of a material is a measure of the average kinetic energy of the particles that make up the material

KelvinTemperature

Average Kinetic EnergyThe Kelvin ScaleCould Kinetic Energy be as low as zero no particle motion at all ?!? As a substance is cooled, it loses more of its kinetic energy. The temperature at which a substance would have ZERO Kinetic Energy is called ABSOLUTE ZERO.No particles would be moving at all.The speed & kinetic energy = zeroThe Kelvin ScaleThe Kelvin Scale is defined so that the temperature of a substance is directly proportional to the average kinetic energy of the particles

The zero on the Kelvin scale corresponds to zero kinetic energyTherefore, absolute zero corresponds to zero on the Kelvin ScaleThe Kelvin ScaleA zero reading on the Celsius or Fahrenheit scales does NOT correspond to zero kinetic energy - atoms are still moving at Oo C (freezing) and Oo F (its below freezing, but atoms are still moving!) K oC oF_____373_______100_______ 212__________________boiling pt. (water)_____273_______0__________32__________________freezing pt. (water)

_____0_________-273_______-459_________________Absolute zero

Answer This!What is the advantage of using the Kelvin scale?No negative numbers makes calculations simple

Has Absolute Zero ever been reached?No, but using a laser-cooling technique that could one day allow scientists to observe quantum behavior in large objects, MIT researchers have cooled a coin-sized object to within one degree of absolute zero. {ScienceDaily (Apr. 8, 2007) }Temperature ConversionsSince the Celsius degree& the kelvin are the same size, and Kelvin readings are 273 degrees higherthan Celsius readings, simply add 273 to the Celsius reading to convertto Kelvin:

Tk = (Tc + 273) K

Temperature ConversionsSimilarly, a Kelvin reading can be expressed as a celsius reading by subtracting 273:

Tc = (Tk 273) oC

Temperature ConversionsTk = (Tc + 273) KTc = (Tk 273) oC

Complete the following conversions using the equations above:

TemperatureCelsiusKelvinMelting point of iron1808Household oven350Food freezer255Sublimation point of dry ice-78.5Boiling point of nitrogen77.4Temperature ConversionsTk = (Tc + 273) KTc = (Tk 273) oC

Complete the following conversions using the equations above:

TemperatureCelsiusKelvinMelting point of iron15351808Household oven350623Food freezer-18255Sublimation point of dry ice-78.5194.5Boiling point of nitrogen-195.677.4Because Fahrenheitdegrees are smaller than Celsius degreesthe conversionequation is a bit morecomplex:

oC=5/9(oF-32)

oF=9/5oC + 32

Temperature Conversions

Temperature ConversionsoC=5/9(oF-32) To convert from Fahrenheit TO Celsius1) subtract 32 from the Fahrenheit temp.2) multiply by 53) divide by 9(Do what is in the parenthesis FIRST)

Convert 120 oF into celsius:

Temperature ConversionsoF=9/5oC + 32To convert from Celsius TO Fahrenheit1) multiply by 92) divide by 53) add 32(NO parenthesis, so multiply & divide FIRST)

Convert 22oC into Fahrenheit:Temperature ConversionsoC=5/9(oF-32) oF=9/5oC + 32

Using the above equations, convert the following:

TemperatureCelsiusFahrenheitA warm day25Body temperature98.6Room temperature20Freezing point of water32Temperature ConversionsoC=5/9(oF-32) oF=9/5oC + 32

Using the above equations, convert the following:

TemperatureCelsiusFahrenheitA warm day2577Body temperature3798.6Room temperature2068Freezing point of water032HOMEWORKComplete the Temperature Conversions worksheet for TOMORROWMass & Speed of ParticlesThe Kinetic Energy of a moving object depends on both its mass AND its speed

A bowling ball will have more kinetic energy & will knock over more pins the faster it is moving

Mass & Speed of ParticlesA loaded shopping cart will have more kinetic energy than an empty cart being pushed at the same speed

It takes more work and more kinetic energy to move heavier objects.

DiffusionThe process by which particles of matter fill a space because of random motion.

The rate of diffusion of a gas depends upon its kinetic energy, that is, on the mass and speed of its moleculesThe faster the speed, the faster the diffusionThe lighter the molecule, the faster its diffusionChanging StatePhysical change of matter from solid to liquid to gas.

Temperature plays an important role in changing states.

There are five processes involved in changing states: evaporation, sublimation, condensation, boiling, and freezing

EvaporationThe process by which particles of a liquid form a gas by escaping from the surface.

The area of the surface, as well as the temperature and humidity, affects the rate of evaporation

Which will evaporate faster?

EvaporationLiquids that evaporate quickly, like perfume and paint, are called volatile liquids.

We spray perfume on our skin to increase the volatility and scent by increasing the size of the surface area where evaporation takes place.

Evaporation

As liquids evaporate, they cool

This is the reason we sweat on a hot day. As the liquid evaporates from our skin, it cools us down.

SublimationSome solids can change into a gas directly without melting first.

This process by which particles of a solid escape from its surface and form a gas is called sublimation

SublimationDry ice (solid CO2) sublimes.

Ice can also sublime. Molecules of ice can leave the surface and become water vapor, which then freezes. This is the cause of freezer burn.Potpourri molecules sublime into the air as fragrance.

CondensationCondensation is the reverse of evaporation.

Gas particles come closer together (they condense) and form a liquid or a solid.

The term vapor is used to describe the gaseous state of a substance that is liquid at room temperature

Vapor Pressure and BoilingIn a closed container, when the particles of a substance are evaporating and condensing at equal rates, equilibrium has been reached.

The pressure exerted bythe vapor in equilibriumwith its liquid is itsvapor pressure.

Vapor Pressure and BoilingThe value of the vapor pressure of a substance indicates how easily the substance evaporates.

Volatile substances, like alcohols, have a high vapor pressure, which means they evaporate easily.Vapor Pressure and BoilingIn the same way that kinetic energy and temperature are related, temperature and vapor pressure are also related.

The evaporation rate is higher at higher temperatures

Vapor Pressure and BoilingThe boiling point of a liquid is thetemperature when its vapor pressure equals the pressure exerted on the surface of the liquid.

In an open container, the temperature rises until the vapor pressure equals atmospheric pressure. Small bubbles of vapor form below the surface and rise. The liquid boils.

Vapor Pressure and BoilingWhen the pressure being exerted on a liquid increases, it takes more energy to raise the vapor pressure of that liquid to get it to boil. The boiling point temperature also increases.

If there is less pressure being exerted on a liquid, the boiling point temperature decreases.Vapor Pressure and BoilingTHINK ABOUT IT!Why do foods cooked in boiling water at higher altitudes need to be cooked LONGER?

Vapor Pressure and BoilingTHINK ABOUT IT!Why do foods cooked in boiling water at higher altitudes need to be cooked LONGER? Because the LOWER atmospheric pressure at high altitudes allows the water to boil at a lower temperature requiring a longer time to cook.

Heat of VaporizationAs you heat a substance, the temperature increases. Once the substance begins to change state from a liquid to a gas, the temperature stops rising. The energy that is being applied is being used for the state change. Once the state change is complete, the temperature will once again rise.

Liquid water and water vapor have the same Kelvin temperature during boiling.Heat of VaporizationChanges in Temperature as a solid is heated

gas

temp liquid

solid

timeHeat of Vaporization is the amount of energy absorbed when 1kg ofliquid vaporizes at its normal boiling point

Heat of VaporizationChanges in Temperature as a solid is heated

gas

temp liquid

solid

timeWhat do the plateaus on the graph represent?Heat of FusionAs you cool a substance, the temperature decreases. Once the substance begins to change state from a liquid to a solid, the temperature stops decreasing. Once the state change is complete, the temperature will once again decrease.

Heat of FusionChanges in Temperature as a gas is cooled

temp

time

Heat of Fusion is the energy released as 1 kg of a substance solidifies at its freezing pointMelting point - The temperature of a solid when its crystal lattice begins to disintegrate and becomes a liquid

Freezing point The temperature of a liquid when it begins to form a crystal lattice and becomes a solid