Thermal Chemistry Chapter 8 Heat and you. 11.1 The Flow of Energy Law of Conservation of Energy:...
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Transcript of Thermal Chemistry Chapter 8 Heat and you. 11.1 The Flow of Energy Law of Conservation of Energy:...
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
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!
– 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)
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)
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?
- 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.
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SUMMER
Water is cooler than the land during summer. Now the oceans cools the coastal cities.
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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
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