Spark 09/22/2011 zOn a very warm day at the beach, which heats up faster, the water or the sand? zOnce night rolls in, which cools faster? zIf some materials heat up faster than others, although exposed to the same energy, then where does the energy go if something is not getting hotter? yWhy might some materials heat up faster than others?

Reading Questions zRead the Matter document up to “Temperatures in Kelvin” zWhat is the KMT? zWhat is the difference between heat and temperature? zWhy is the Kelvin temperature scale used? zHow does the K scale convert to Celcius?

Enthalpy and Heat The study of energy and its transformations is known as thermodynamics.thermodynamics. EnergyEnergy is commonly defined as the capacity to do work or to transfer heat. WorkWork is energy used to cause an object with mass to move. HeatHeat is energy used to cause the temperature of an object to increase.

Enthalpy and Heat Kinetic energy is the energy of motion, represented by the equation: E k = 1 / 2 mv 2 Atoms and molecules have mass and are in motion, therefore they have kinetic energy.

Enthalpy and Heat zThe SI unit for energy is the joule: J = 1 kg-m 2 /s 2 zA 2 kg mass moving at 1 m/s possesses a kinetic energy of 1 J: zE k = 1 / 2 mv 2 = 1 / 2 (2 kg) (1 m/s) 2 = 1 kg-m 2 /s 2 = 1 J zSince a joule is a small amount of energy, the unit kilojoules, kJ, is often used when describing chemical reactions.

Enthalpy and Heat zTraditionally, energy changes in chemical reactions have been expressed in calories, a non-SI unit. zA calorie was originally defined as the amount of heat energy required to raise the temperature of 1 g of water from 14.5 o C to 15.5 o C. It is now defined in terms of the joule: z1 cal = J (exactly)

Enthalpy and Heat zA related energy unit used in nutrition is the nutritional Calorie (note the capital letter). z1 Cal = 1000 cal = 1 kcal

E N T H A L P Y - H heat content in matter:

E N T H A L P Y - H heat content in matter: natural systems tend to go from a state of high energy to a state of low energy.

E N T H A L P Y The phases of matter represent "classes" of molecular motion found at different temperatures.

E N T H A L P Y The phases of matter represent "classes" of molecular motion found at different temperatures. X Kinetic Energy

E N T H A L P Y The phases of matter represent "classes" of molecular motion found at different temperatures. X HEAT

Hot Coffee Thermal E = 4 Internal E = 2 Solids = 1 Liquids = 2 Gases = 3 Chemical = 0

Coffee Before Coffee After Total Energy = 7 units Total Energy = 5 units Missing 2 units of E: Where did they go?

How can we diagram energy flow when a cup of coffee cools? zEnergy Flow Diagram yIs energy flowing in or out of the system? y2 units of energy leave causing the coffee to cool. Cup of Hot Coffee E E 7 units - 2 units =5 units

Spark Does hot water or cold water freeze faster? Explain using the KMT. Are you aware of the Mpemba Effect? What are the four conditions that make the Mpemba Effect possible?(p2-3) Do you have an explanation for the Mpemba Effect?

HMMMM… Can water boil if it’s cold? Explain using the KMT

Heat zMatter does not contain heat, it contains energy (kinetic, thermal, internal energy, chemical energy). zHeat is energy that is transferred from hot to cold zHeat is measured in calories or Joules z1 calorie = J zMeasure average kinetic energy with a thermometer and call it temperature zHow can we measure heat if things don’t heat and cool the same way?

Specific Heat Capacity zThink of it as heating ability… zThe amount of heat energy that is required to raise the temperature of one gram of a substance by one degree Celsius is called the specific heat capacity, or simply the specific heat, of that substance. zWater, for instance, has a specific heat of 1.0 calorie per gram degree Celsius [1.0 cal / (g x o C)]. Water becomes our standard for studying energy.

Specific Heat Capacity Water So: It takes 1 calorie of heat to raise 1 gram of water 1 degree How many calories are released if 1 gram of water cools 1 degree? How many calories are needed to heat 1 gram of water at O o C to boiling (100 o C)? 1 calorie 100 cal

Lab Burners and BTUs

BTU Inquiry Lab Tips Rate of BTU production be lab burner. 1 BTU = Nrg to increase 1 lb of o F, 1 o F Convert measurable metric masses and temperatures into BTU’s and predict the time to get a hypothetical rate (BTU/sec)

E N T H A L P Y q = U + P V q = heat gained or lost U = internal energy P = Pressure V = volume See Energy notes

Spark 09/27/2011 How much energy is needed to melt a 10 lb bag of party ice at 0 o C? (heat of fusion = 334 J/g or 80 cal/g) There are 2.2 lbs/1 kg zH fus - heat of fusion z The amount of heat needed to change one gram of a solid into a liquid at its melting point.

E N T H A L P Y H fus - heat of fusion As energy is added to a solid at its melting point, ALL the energy is used to increase the kinetic energy of the molecules during the phase change.

E N T H A L P Y H fus - heat of fusion The amount of heat needed to change one gram of a solid into a liquid at its melting point.

Every phase change is accompanied by a change in the energy of the system.

As the temperature of a solid increases, its particle vibration increases.

When a solid melts, its particles are freed to move with respect to one another.

This melting process is called fusion.

The increased freedom of motion of the molecules or ions comes at a price...

measured by the heat of fusion, or enthalpy of fusion,  H fus

solid/liquid phase change q = m  H fus q = heat gained or lost m = mass  H fus = heat of fusion

E N T H A L P Y H fus H 2 O = 334 J/g H fus lead = J/g

As the temperature of a liquid increases, the molecules move with increasing energy.

When increasing temperature, the concentration of gas-phase molecules just above the surface of the liquid increases.

These gas-phase molecules exert a pressure on the liquid called vapor pressure.

This vapor pressure increases with temperature until it equals the atmospheric pressure.

This is the boiling point of the liquid.

The energy required to cause this transition..

is called the heat of vaporization or enthalpy of vaporization,  H vap

E N T H A L P Y As energy is added to a liquid at its boiling point, ALL the energy is used to increase the kinetic energy of the molecules during the phase change.

E N T H A L P Y H vap - heat of vaporization The amount of heat needed to change one gram of a liquid into a gas at its boiling point.

liquid/gas phase change q = m  H vap q = heat gained or lost m = mass  H vap = heat of vaporization

E N T H A L P Y H vap H 2 O = 2260 J/g

is used to measure heat change

Heat of Fusion of Ice

Spark q = m x ΔT x s 50.0 grams of hot water (65.0 o C) are added to a calorimeter that has 25.0 grams of water at 5.0 o C. After mixing the final temperature reached was 44.0 o C. 1 cal = J = E to raise 1 g H 2 O 1 o C How much energy was released from the hot water? How much was absorbed by the cold water? Is energy being conserved? Does the nrg released = the nrg absobed?

Calorimeter Constant

Heat of Solutions and Reactions

Spark With your group, calculate your mean calorimeter constant. Send a representative to me with your value for spreadsheet credit. Be sure that all group members know what the calorimeter constant reflects!

What is How “well” a substance heats up… How much energy is needed to heat something up…

Specific Heat Capacity The heat required to raise the temperature of one gram of a substance by one Celsius degree.

change temp within phase q = m  C p q = heat gained or lost m = mass  = “change in temperature” C p = specific heat capacity

Specific Heat Capacity zThe amount of heat energy involved in changing the temperature of a sample of a particular substance depends on three parameters -- the specific heat of the substance, the mass of the sample, and the magnitude of the temperature change. zThe Greek letter delta (Δ) is used to indicate a change. yΔ T = temperature final - temperature initial

The General Idea Behind Specific Heat Labs zBoth ice or a heated sample will be placed into a crude calorimeter, consisting of water contained in a plastic foam cup. Shortly after mixing, the sample will have come to the same temperature as the water or the water temperature will increase or decrease depending on the change. zBecause Styrofoam is a good insulator, heat cannot easily escape from the calorimeter to the surroundings.

Specific Heat Labs zThe heat lost or gained by the sample should be equal to the heat gained or lost by the water. zThe amount of heat energy gained by the water will be calculated in the following manner: heat gained water = specific heat water X mass water X ΔT water

zThe heat lost by the sample is given by a similar equation: zheat lost sample = specific heat sample X mass sample X ΔT sample zBecause the heat gained must equal the heat lost, a third equation can be written: zspecific heat water X mass water X ΔT water = specific heat sample X mass sample X ΔT sample

zThe specific heat of water is known. zThe temperature changes of the water, and of the sample, can be measured, as can the mass of the water and the mass of the sample. zUsing this data, the specific heat of the sample can be calculated. z Calorimetry values are all determined based on the temperature changes of the water sample.

Which has the greater? Cu H2OH2O or

Specific Heat Capacity C p of ice = 2.06 J/g.C o C p of water = 4.18 J/g.C o C p of steam = 2.02 J/g.C o C p of copper =.385 J/g.C o

q=m  H vap change phase q=m  H FUS - change phase q=m  C p - change temp

How much heat is needed to convert 250 grams of ice at -30 o C to vapor at 150 o C? 1. Change temp of ice 2. Melt ice 3. Change temp of liquid water 4. Vaporize water 5. Change temp of vapor 6. Add total heat used

Step 1 raise temp of ice q = m  T C p q = (250g) (30 C o ) (2.06 J/g. C o ) q = 15,450 Joules

Step 2 melt ice q = m  H fus q = (250g) (334 J/g) q = 83,500 Joules

Step 3 raise temp of liquid water q = m  T C p q = (250g) (100 C o ) (4.18 J/g. C o ) q = 104,500 Joules

Step 4 vaporize liquid water q = m  H vap q = (250g) (2260 J/g) q = 565,000 Joules

Step 5 raise temp of water vapor q = m  T C p q = (250g) (50 C o ) (2.02 J/g. C o ) q = 25,250 Joules

Step 6 q = 15,450 83, , ,000 25,250 q = 794,000 Joules

Specific Heat of a Metal

Heat of Combustion of Wax

Spark Get your materials for the specific heat lab. 3 groups may use burners otherwise use a hot plate. Use 2 foam cups instead of one Calorimeter water should be cold. I will give you your metals once you have everything else.

P h a s e D i a g r a m A g r a p h s h o w i n g t h e p h a s e s o f m a t t e r a s t h e y r e l a t e t o t e m p e r a t u r e a n d p r e s s u r e.

M a j o r p o i n t s o n a p h a s e d i a g r a m Normal Atmospheric Pressure Triple point Boiling Point Boiling Point Melting point Melting point Critical temperature Critical temperature

kPa normal atmospheric pressure

TP Triple Point

TbTb Normal boiling point

TmTm Normal melting point

TcTc Critical temperature

V a n d e r W a l l s A t t r a c t i o n T h e f o r c e o f a t t r a c t i o n b e t w e e n m o l e c u l e s m o l e c u l e s

Calories in a Peanut