Chapter 6 Notes Heat & Temperature Calculations. Temperature = a measure of the AVERAGE kinetic...

Chapter 6 NotesChapter 6 Notes

Heat & Temperature Heat & Temperature CalculationsCalculations

TemperatureTemperature = a measure of = a measure of the AVERAGE the AVERAGE kinetic energy kinetic energy in the in the substance.substance.

Celsius (°C)Celsius (°C) Fahrenheit Fahrenheit

(°F)(°F) Kelvin (°K)Kelvin (°K)

NEED TO FIND FORMULA

°C°F 1.8°C + 32

°F°C °F – 32/1.8

°C°K °C + 273

°K°C °K – 273

°K°F °K °C °F

0°K0°K == absolute zero = all absolute zero = all molecular motion stopsmolecular motion stops

HH220 distilled water (pure 0 distilled water (pure water)water)

melting point = 0°Cmelting point = 0°C boiling point = 100°Cboiling point = 100°C

Energy (heat)Energy (heat) measure in measure in Joules, BTUs (British Thermal Joules, BTUs (British Thermal Units) calories and Calories.Units) calories and Calories.

1 calories = 4.186 Joules1 calories = 4.186 Joules 1 BTU = 252 calories1 BTU = 252 calories 1 Calorie = 1000 calories1 Calorie = 1000 calories

States of Matter States of Matter Also called Phases of MatterAlso called Phases of Matter

SolidsSolids

LiquidsLiquids

Vapors (gases)Vapors (gases)

SolidsSolids

Have a definite shapeHave a definite shape

Have a definite volumeHave a definite volume

Particles VIBRATE in placeParticles VIBRATE in place

LiquidsLiquids

Have NO definite shapeHave NO definite shape

Have definite volumeHave definite volume

particles SLIDE freelyparticles SLIDE freely

Gases (vapor)Gases (vapor)

Have NO definite shape Have NO definite shape

Have NO definite volumeHave NO definite volume

particles fill the particles fill the volume of the volume of the containercontainer

Solids, Liquids & GasesSolids, Liquids & Gases

SolidsSolids = can form = can form crystalscrystals = = solid where the particle are solid where the particle are arranged into repeating arranged into repeating patterns.patterns.Liquids Liquids = physical property = physical property of of ViscosityViscosity = “thickness” – = “thickness” – the resistance to flow.the resistance to flow.Gases Gases = volume of gases = volume of gases depend greatly on pressure depend greatly on pressure and temperature.and temperature.

Phase ChangesPhase Changes

MeltingMeltingFreezingFreezingVaporizationVaporizationCondensationCondensationSublimationSublimationphysical physical changeschanges

MeltingMelting

the process of changing from a solid to the process of changing from a solid to a liquid a liquid

energy is being energy is being put intoput into the substance the substance

melting pointmelting point = the temperature at = the temperature at which melting occurs – physical which melting occurs – physical propertyproperty

the melting point of water is the melting point of water is 0ºC0ºC

FreezingFreezing

the process of changing from a liquid the process of changing from a liquid to a solid to a solid energy is being energy is being pulled outpulled out of the of the substancesubstancefreezing point freezing point == same temperature as same temperature as the melting point the melting point (used mainly in weather)(used mainly in weather)

VaporizationVaporization

the process of changing from a liquid to a the process of changing from a liquid to a gas gas

energy in being energy in being put intoput into the substance the substance

evaporationevaporation

boilingboiling

EvaporationEvaporation

vaporization that occurs at the vaporization that occurs at the surfacesurface of the liquid of the liquid

BoilingBoiling

vaporization that vaporization that occurs throughoutoccurs throughout the liquidthe liquidboiling pointboiling point = = the temperature at the temperature at which boiling occurswhich boiling occursthe boiling point of water is the boiling point of water is 100ºC100ºC

CondensationCondensation

the process of changing from a gas to the process of changing from a gas to a liquida liquid

energy is being energy is being pulled outpulled out of the of the substancesubstance

SublimationSublimation

the process of changing from a solid to a the process of changing from a solid to a gasgas

energy is being energy is being put intoput into the substance the substance

ex: dry ice (COex: dry ice (CO22))

heat of fusion

Heating Heating of waterof water

0°C

100°C

heat of vaporization

ICE

WATER (liquid)

STEAM

Heat TransferHeat Transfer

ConductionConductionConvectionConvectionRadiationRadiation

ConductionConduction transfer of heat by direct contact transfer of heat by direct contact

(molecule to molecule)(molecule to molecule) metals are good conductorsmetals are good conductors poor conductors = poor conductors = insulatorsinsulators

ConvectionConvection transfer of heat by “transfer of heat by “convection currentsconvection currents” ”

warm fluids are less dense than colder fluid warm fluids are less dense than colder fluid thus warm fluids rise and cold fall.thus warm fluids rise and cold fall.

not possible in solidsnot possible in solids fluidfluid = anything that flows (liquids & gases) = anything that flows (liquids & gases) hot air balloons, “convection” ovenshot air balloons, “convection” ovens

RadiationRadiation transfer of heat by electromagnetic transfer of heat by electromagnetic

waveswaves some wavelengths of some wavelengths of infraredinfrared & &

ultravioletultraviolet only type of transfer that can occur only type of transfer that can occur

through empty spacethrough empty space sun sun Earth Earth

Specific HeatSpecific Heat

The amount of heat needed to The amount of heat needed to raise the temperature of one raise the temperature of one gram of a substance on degree gram of a substance on degree Celsius.Celsius.

Factors in Specific HeatFactors in Specific Heat

types of substance (C) types of substance (C) mass of the substance mass of the substance

(m)(m) how much of a how much of a

temperature change temperature change (∆T)(∆T)

CC = specific heat = specific heat constantconstant

mm = mass = mass ∆∆TT = difference in = difference in

the temperaturethe temperature

Specific Heat Specific Heat CalculationsCalculations

∆∆QQ = amount of heat absorbed = amount of heat absorbed (difference in the heat or heat (difference in the heat or heat change)change)

∆∆Q Q == m m xx ∆T ∆T xx C C

The specific heat of waterThe specific heat of water= = 1.0 cal/g°C1.0 cal/g°C or or = = 4.2 joules/ g°4.2 joules/ g°CC

EXAMPLE #1EXAMPLE #1::How many calories are absorbed by a How many calories are absorbed by a pot of water with a mass of 500 grams pot of water with a mass of 500 grams in order to raise the temperature from in order to raise the temperature from 20°C to 30°C?20°C to 30°C?

C = C = 1.0 cal/g°C1.0 cal/g°C m = m = 500 grams500 grams ∆∆T = T = 10°C10°C (30-20) (30-20)

∆∆Q Q == m m xx ∆T ∆T xx C C ∆∆Q = (500 g)(10°C)(1.0 cal/g°C)Q = (500 g)(10°C)(1.0 cal/g°C)

∆∆Q = 5000 Q = 5000 caloriescalories

EXAMPLE #2EXAMPLE #2::How many joules are absorbed by a How many joules are absorbed by a pot of water with a mass of 500 grams pot of water with a mass of 500 grams in order to raise the temperature from in order to raise the temperature from 20°C to 30°C?20°C to 30°C?

C = C = 4.2 J/g°C4.2 J/g°C m = m = 500 grams500 grams ∆∆T = T = 10°C10°C (30-20) (30-20)

∆∆Q Q == m m xx ∆T ∆T xx C C ∆∆Q = (500 g)(10°C)(4.2 J/g°C)Q = (500 g)(10°C)(4.2 J/g°C)

∆∆Q = 21,000 Q = 21,000 JoulesJoules

Phases ChangesPhases Changes

Heat of fusionHeat of fusion (H (Hff)) the heat energy needed to melt (or the heat energy needed to melt (or

freeze) a substance. freeze) a substance. All heat being put into the substance All heat being put into the substance

goes to the melting processgoes to the melting process thus the temperature does not thus the temperature does not

change while the substance is change while the substance is melting.melting.

Phases ChangesPhases Changes

Heat of vaporizationHeat of vaporization (H (Hvv)) the heat energy needed to boil (or the heat energy needed to boil (or

condense) a substance. condense) a substance. All heat being put into the substance All heat being put into the substance

goes to the boiling processgoes to the boiling process thus the temperature does not thus the temperature does not

change while the substance is change while the substance is boiling.boiling.

Heat & Phases ChangesHeat & Phases Changes

HHff = = mass x Hmass x Hff constant constant The heat of fusion of water = The heat of fusion of water = 340 J/g340 J/g HHvv = = mass x Hmass x Hvv constant constant The heat of vaporization of water = The heat of vaporization of water = 2300 2300

J/gJ/g

EXAMPLE:EXAMPLE:How many joules of heat are How many joules of heat are necessary to necessary to meltmelt 500 g of 500 g of iceice??

CChfhf = 340 J/g = 340 J/g m = 500 gm = 500 g H = CH = Chfhf x m x m H = (340 J/g)(500 g)H = (340 J/g)(500 g)H = 170,000 JH = 170,000 J