Thermal ChemistryChapter 8

Heat and you

11.1 The Flow of Energy

• Law of Conservation of Energy: energy can neither be created nor destroyed, but can change forms.

• Energy is the capacity to do work or to supply heat

• Example:

• Energy needed to walk….where did this come from? Go “backwards” to determine the original source of energy

Endothermic and Exothermic processes

• Endothermic…

• absorb heat from the surrounding area(s)

• Has a cooling effect on environment

• Exothermic…• releases heat to the

surrounding area(s)• System becomes

cooler, environment becomes warmer

Car’s cooling system

• http://auto.howstuffworks.com/cooling-system.htm

Refrigerators

• http://home.howstuffworks.com/refrigerator.htm

• Check it out!!! You’ll be able to find out why the back of your refrigerator is warm!

HEATHEATHEATHEAT HEATHEATHEATHEAT HEATHEATHEATHEAT HEATHEATHEATHEAT

– Vibrational energy is transferred from one particle to the next

» One particle collides with the next particle and so on; and so on – down the line

An Ice Cold Spoon A Hot Spoon

11.2 Measuring and Expressing Heat Changes

• Thermo chemical equations show the accompanying heat of reactions at a constant pressure

• Calorimetry measures heat changes associated with chemical reactions and phase changes

• Heat Lost [q(lost) ] = -Heat Gained [ q(gained) ] = mass x specific heat x change in temp

• 50 grams of water is heated from 20 to 40 degrees Celsius, how much heat will it take in joules? Cwater=4.184 J/gr0C

• How much heat is needed to melt 580 grams of ice that starts at -280C ? Cice = .5 J/gr0C

Definitions

• Heat can be measured in Joules or calories.

• Specific heat-the heat necessary to raise one gram of any substance 1 degree celsius.

• 4.184 Joule= 1calorie• =specific heat of water

• 1 calorie - the specific heat of pure water

• 1 dietary Calorie (written with a capital C) = 1000 calories. Refers to the amount of potential energy in food molecules.

Specific Heat Values of Metals (Joules/gr 0C)

• Metal Specific Heat• Copper .386• Aluminum .900• Iron .452• Lead .128• Zinc .388• Tin .228• Air 1.4• Water 4.184

Specific heat of some common substances

• Substance calories/(g x degrees Celsius)

• water 1.00

• alcohol 0.58

• ice 0.5

• wood 0.42

• steam 0.4

• chloroform 0.23

• aluminum 0.21

• glass 0.12

• iron 0.11

Specific heat of some common substances

• Substance calories/(g x degrees Celsius)

• water 1.00

• alcohol 0.58

• ice 0.5

• wood 0.42

• steam 0.4

• chloroform 0.23

• aluminum 0.21

• glass 0.12

• iron 0.11

Calculating Specific Heat

Heat Lost/Gained = (mass) (Specific Heat) (Change in Temp)

Joules = (grams) (Joules/gr-0C) (0C)

For a metal dropped into water:

Heat lost by metal = heat gained by water(mass) (Specific Heat) (Change in Temp)= (mass) (Specific Heat) (Change in Temp)

-Solve for Specific Heat of the metal as an unknown

Cmetal= (masswater)(Sp. Heatwater)(Change in Tempwater)

(massmetal) (Change in Tempmetal)

Calorimetry

Food and CaloriesHow many calories do you need?• The Easy Way

If all of those calculations seem too confusing or tedious, you can roughly estimate your daily calorie requirements using this simple formula:

• For sedentary people: Weight x 14 = estimated cal/day

• For moderately active people: Weight x 17 = estimated cal/day

• For active people: Weight x 20 = estimated cal/day

• 3500 calories = 1 lb. Fat storage

11.3 Heat in Changes of State

• The molar heat of fusion, solidification, and vaporization and condensation describe the quantity of heat transferred to or from a system when 1 mole of substance undergoes a change of state at a constant temp.

11.4 Calculating Heat Changes

• Hess’s Law: in a reaction that is the sum of two or more other reactions a change in heat for the overall process is the sum of the change of heat values for all of the parts of the reactions

• The heat of the reaction for the formation of 1 mole of a compound from its elements in standard states is the heat of the reaction of the formation Hf

o

• The standard heat of a reaction change for a reaction can be calculated from the Hf

o of the reactants and products

Calculating Specific Heat

Heat Lost/Gained = (mass) (Specific Heat) (Change in Temp)

in other words

Specific Heat = heat input / mass (g) * change in temperature (degrees Celsius)

joules or calories can be used.

Find the heat needed to increase the temperature of 5.6 grams ofaluminum by 24 degrees Celsius. (refer to the chart on p. 296 of the textbook, “Specific Heat Capacities of Some Common Substances”).

0.9Joules/gr-oC (specific heat of aluminum)

Heat in time

Temp

ice

water

steam

ice water

water steam100C

0C

Heating Curve for Water

Oranges…An Example!• Farmers farm oranges in the winter oranges could

FREEZE!!! To prevent this they pour water on the oranges and let the water freeze instead! (poor water) Freezing gives off a lot of heat. So when the water freezes it gives the heat to the oranges!! HOW NICE. Freezing is exothermic…so the orange absorbs the heat from the water as the freezing occurs.

Ocean Influence on Land Weather

• Why are weather conditions different for communities located near the ocean compared to those located more inland?

- How does the Ocean Affect the Weather?

- Water, gases, and energy are exchanged between the ocean and atmosphere

- Moderates the surface temperatures of the ocean

- Shapes the Earth’s weather and climate- Generates most of the ocean’s waves

This Exchange:

-WEATHER is the state of the atmosphere at a specific place and time - CLIMATE is the long-term (30 year) average of weather in an area- Both weather and climate are affected by the ocean

- Lets see some examples of how the ocean influences our weather

                                                                                                                                      

                                          

Ever Notice???

Our weather here is different than the weather inland?

Ocean’s effect on local weather

WINTER

Water is warmer than land during winter. The ocean warms the cities right along the coast.

54

52

41

5043

SUMMER

Water is cooler than the land during summer. Now the oceans cools the coastal cities.

91

89

101

8798

Why is there almost always a breeze at the beach?

- The land and water heat at different rates

- Land heats and cools faster than the water

Cooler Ocean Warmer Land

Warmer temperatures cause air to riseOnshore Breeze

Cool air sinks to fill in the space

Afternoon Breezes are onshore

Clouds Form

Afternoon Showers

Warmer Ocean Cooler Land

Warmer temperatures cause air to rise

Offshore Breeze

Cool air sinks to fill in the space

Evening Breezes are offshore

- Great masses of warm, humid, rotating air

- Occur in tropical oceans

-Called “Hurricanes” in the North Atlantic

“Typhoons” in the Western Pacific

“Cyclones” in the Indian Ocean

“Wili-Wilis” near Australia

- Hurricanes start out as Tropical Depressions (Low Pressure Zones) off the coast of Africa or in the Caribbean

- Next, when their wind speeds reach 40 mph they become Tropical Storms (and they get a name)

- They become Hurricanes once they reach a wind speed of 74mph

                                                                        

Typical Hurricane Path is around the Atlantic’s high pressure cell

•Category One -- Winds 74-95 miles per hour •Category Two -- Winds 96-110 miles per hour •Category Three -- Winds 111-130 miles per hour •Category Four -- Winds 131-155 miles per hour •Category Five -- Winds greater than 155 miles per hour

Saffir-Simpson Scale

Most hurricanes make landfall in the Southeast U.S. of Gulf States

Names for Atlantic Basin Tropical Cyclones

2002

ArthurBerthaCristobalDollyEdouardFayGustavHannaIsidoreJosephineKyleLiliMarcoNanaOmarPalomaReneSallyTeddyVickyWilfred

2003

AnaBillClaudetteDannyErikaFabianGraceHenriIsabelJuanKateLarryMindyNicholasOdettePeterRoseSamTeresaVictorWanda

2004

Alex Bonnie Charley Danielle EarlFrancesGastonHermineIvan Jeanne Karl LisaMatthewNicole Otto PaulaRichardShary TomasVirginieWalter

2005ArleneBretCindyDennisEmilyFranklinGertHarveyIreneJoseKatrinaLeeMariaNateOpheliaPhilippeRitaStanTammyVinceWilma

2006AlbertoBerylChrisDebbyErnestoFlorenceGordonHeleneIsaacJoyceKirkLeslieMichaelNadineOscarPattyRafaelSandyTonyValerieWilliam

2007*AllisonBarryChantalDeanErinFelixGabrielleHumbertoIrisJerryKarenLorenzoMichelleNoelOlgaPabloRebekahSebastienTanyaVanWendy

A hurricane’s energy source is warm seawater (>80°F)