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Specific Heat. What are the building blocks? This concept does not involve building or breaking down of molecules but might involve a mixture of elements.

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Presentation on theme: "Specific Heat. What are the building blocks? This concept does not involve building or breaking down of molecules but might involve a mixture of elements."— Presentation transcript:

1 Specific Heat

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3 What are the building blocks? This concept does not involve building or breaking down of molecules but might involve a mixture of elements or compounds. Specific Heat How water heats up or cools down is the standard for all other materials. There is usually an interest to how metals heat up. However, all materials heat up differently.

4 Energy measured in calories is used for this concept. A calorie is defined as The amount of heat energy needed to raise the temperature of one gram of water one degree Celsius. Or the amount of heat energy lost when one gram of water cools one degree Celsius. This calorie is different than the one you hear about for food. A food calorie is 1,000 times larger. It is often written with a capital C

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6 For water, there is one calorie for every one gram and for every degree Celsius. One calorie for each gram and for each degree Celsius. One calorie per gram per degree Celsius. 1 cal g o C Specific Heat involves a rate of heating based on weight

7 Observation: Different materials heat up at different rates. 1 kg of Gold 1 kg of Aluminum Gold heats up about 7 times faster than Aluminum 20 O C 90 O C 20 O C 90 O C

8 1 kg of Water Water takes about 30 times longer to heat than gold, meaning it stores about 30 times more calories. 20 O C 90 O C 20 O C 90 O C Different materials store different amounts of heat energy. 1 kg of Gold

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10 Explained by the difference of the specific heat of water versus soil.

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13 Observation: Different materials heat up at different rates. 1 kg of Gold 1 kg of Aluminum Gold heats up about 7 times faster than Aluminum 20 O C 90 O C 20 O C 90 O C

14 1 kg of Gold 1 kg of Aluminum By the time aluminum heats up to 90 O C it will have stored 7 times more calories of heat than the gold did. 20 O C 90 O C 20 O C 90 O C Different materials store different amounts of heat energy.

15 1 kg of Water 1 kg of Aluminum Water takes about 5 times longer to heat than aluminum, meaning it stores about 5 times more calories. 20 O C 90 O C 20 O C 90 O C Different materials store different amounts of heat energy.

16 1 kg of Water 1 kg of water would take 1,000 calories for each degree. Our 70 0 C increase would take 1,000 x 70 = 70,000 calories. 20 O C 90 O C 1 calorie is defined as the amount of energy needed to raise 1 gram of water 1 degree Celsius

17 1 kg of Water 1 kg of water would take 1,000 calories for each degree. Our 70 0 C increase would take 1,000 x 70 = 70,000 calories. 20 O C 90 O C 1 mL or 1 cm 3 (cc) of water has the mass of 1 gram. 1,000 mL = 1 Liter has mass of 1 kilogram 1 Liter water 70,000 calories = 70 kilocalories 70,000 calories = 70 Calories Food calories

18 The specific heat of water is 1 calorie per 1 gram per 1 degree Celsius 1 cal g 0 C The specific heat of water is 1 calorie per 1 gram per 1 degree Celsius 1 cal g 0 C Specific Heat of Water = Joules = 1 calorie Joule = The energy used by 1 watt for 1 second

19 1 cal g 0 C __ g X __ 0 C X Let the dimensions tell you how to solve problems.

20 The specific heat of other materials can be calculated by measuring the temperature rise of water. Blacksmiths may have been the first to recognize this approach.

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24 Need modern blacksmith

25 The specific heat of other materials can be calculated by measuring the temperature rise of water. Since specific heat is calories per gram per degree (raised/lowered) we need to keep track of what quantities? Grams Water Metal Initial and Final Temperatures Water Metal

26 Conservation of Energy Energy Lost = Energy Gained Calories Lost = Calories Gained Joules Lost = Joules Gained

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28 Winter Survival and a Safe Source of Heat for Field Operations A request for investigation into the heat capacity of available materials

29 Problem with heating tents Heating the inside of tents is dangerous because of the potential for fire and carbon monoxide poisoning. It seems that heating objects outside the tent and then bringing them inside would be safer.

30 Candidates considered for heating are metal objects like aluminum or iron. Rocks found in the vicinity could also be used. Water is another candidate.

31 On a gram for gram basis, water stores heat much more efficiently than any other candidates. However, water can only be brought to 100 degrees Celsius before it boils, and then it wont get any hotter unless placed under pressure, which is dangerous. Water is also a precious commodity in some regions, so risking a spill may not be worth it. Water: Pros and Cons

32 Some of the metal tools and equipment might be used. However, in a quick evacuation of camp it might cause problems if these items are too hot to handle. Metal: Pros and Cons

33 Rocks seem like the best candidate. However, we have no data on how efficient rocks can store heat, especially of rocks containing a mixture of minerals. Rocks: Pros and Cons

34 Needed questionsWhere between extremes What was the mass of the heated rocks? Was it a few one-pound rocks or half a ton of rocks? How hot were the rocks? Were they heated to body temperature or to several hundred degrees in a fire? How cold was the tent? Was it only a cool 50 degrees Fahrenheit or a bone-chilling 20 degrees below zero? How big was the tent? Was it a standard one person tent or a large command post tent? How much did it warm the tent? Did it raise a few degrees or 50 or more degrees? To calculate heat energy released from rocks we could calculate the heat energy gained by the tent, which is difficult because of the different materials in the tent. However, we could use water instead because we know that it takes one calorie to raise one gram of water one degree Celsius. Heat energy released by rocks = Heat energy gained by water Heat energy released by rocks = Heat energy gained by tent. There are stories of soldiers and others who said they heated up rocks, brought them into their tent, and the rocks warmed up the tent. This is good to know, but there is much information missing.

35 In practice, it wouldnt be that easy to find a rock equal to one gram or to drop it into one gram of water. Therefore, the calculations will need to adjust for the mass of the rock and the mass of the water. A rock could be heated by a flame but it would be difficult to measure the rocks temperature. Another way would be to place the rock in boiling water and then measure the temperature of the water. Then the heated rock could be placed in a known amount of water and the temperature rise of the water could be recorded. The rock will begin to cool quickly after being removed from boiling water, so the transfer should be quick. Also shake off any excess water so heating is from rock and not from the hot water. Should be near 100 o C Other heat sources could be used (hotplate, stove top, etc.) If heat gets transferred away from water, then the water wont reach its full temperature. Therefore, insulation is critical. Use two Styrofoam cups. and a cover.

36 Its February and you want to heat up your pool. It is currently 50 o F (10 o C) and you want it raised to 80 o F (27 o C) Using an electric heater, how much will it cost if 1 kilowatt-hour is 10 cents? The pool is 7.0 meters long, 5.0 meters wide and 2.0 meters deep. A. Whats the volume in cubic meters? ______ B. What is the volume in cubic centimeters?___________ C. What is the total grams of the water? ____________ A calorie is defined as the energy needed to raise one gram of water one degree Celsius. D. How many calories will it take to raise the pool water from 10 o C to 27 o C? _______________ E. 1 calorie = 1.1 x kilowatts hours. How many kilowatt-hours will you need? ____________ F. How much will it cost to heat the pool from 50 o F (10 o C) to 80 o F (27 o C)? _______________ grams 17 o C 1 calorie = g. o C calories 1.1x10 -6 kilowatt-hrs = calories kilowatt-hr _______ kilowatt-hours $0.10 = 1 cc of water weighs 1 gram Name: _________________

37 Calories Lost = Calories Gained calories lost by metal = calories gained by water grams x 1 cal x T g 0 C grams x SH x T = grams x SH x (T f - T i ) = grams x 1 cal x (T f - T i ) g 0 C SH x g 0 C amount = calories gained by water g 0 C amount Specific Heat metal = calories gained by metal g 0 C


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