lab12.1 Name Period experiment 12.1 specific heat capacity of a metal Please read and complete this pre-lab prior to performing this experiment.

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3 lab12.1 Name Period experiment 12.1 specific heat capacity of a metal Please read and complete this pre-lab prior to performing this experiment. Theory: Have you observed how some metals stay hot longer than others? Specific heat measures this property: it is the amount of heat required to raise the temperature of one gram of a substance by one degree Celsius. For example, as a 1 g slug of hot lead (Pb) cools in water, it releases joules (j) of heat to the water for each degree that it cools. We can therefore identify metals by measuring the specific heat of an unknown metal, and comparing it to known values. We will do this by heating a metal to 100 O C, then placing it in room temperature water to see how much hotter the water gets. Metals with a high specific heat will heat up the water a lot. We will then calculate the specific heat (called c ) of the metal to identify it. Pre-Lab Questions: 1. Give a definition of specific heat in your own words- don t use the definition above. L1- also provide a formula for specific heat. 2. Why might it be important to use a large mass of metal for these measurements? 3. Why would it be bad if the water didn t fully cover the metal? 4 (challenge question)the specific heat of iron is cal/g O C, it has a density of 7.86 g/cm 3, and a molar mass of g/mol. Determine the specific heat of iron per cubic centimeter (cal/cm 3 0 C) and per mole (cal/mol O C). Please show your calculations. procedure Put water in a calorimeter (a Styrofoam cup) to just cover your metal; mass the water. m water : Take the temperature of the room temperature water in your cup. T water, initial: Take the temperature of the boiling water full of metal (it should be 100 O C) T metal : With a minimum amount of heat loss, transfer your hot metal to calorimeter (cup).make sure metal is submerged. See how hot the water gets. T water, final: Dry your metal and mass it. m metal = 3

4 To find the specific heat of the metal we use the specific heat formula: Or, q = (m)(c)(dt) q c = mdt calculations where q = heat change = j/g O C (see below) c = specific heat m = mass in grams, DT = change in temperature in o C. Strategy: We will find how much heat the water absorbed,(q metal ), realize it all came from the metal (q water = q metal ), then we have enough data to find the specific heat (c) of the metal. Hopefully it matches the specific heat of a known metal. The key assumption we will use is that heat absorbed by water = heat released by metal (q water = q metal ). The specific heat c for water = j/g o C. Study the sample calculation carefully- use it as a template for your own calculation. Sample Calculation: 125 g water, initial temperature of water = 25.6 o C, initial temperature of metal = o C, Final temp of water = C. Mass of metal = 50.0 g. What is the metal? Solution: First we find the heat absorbed by the water, which is also the heat lost by the metal, then solve for the specific heat of the metal. q water = m water c water DT water = (125 g) (4.184 J/g o C) (29.3 o C 25.6 o C) = 1900 J = q m q c metal = m 1900 J = m m DT m (50 g)(115 o C 29.3 o C) = 0.44 J/g o C. Comparing to known values, the metal may be Iron (Fe, c = J/g o C). Your Calculation: g water, initial temperature of water = o C, initial temperature of metal = o C, Final temp of water = 0 C. Mass of metal = g. What is the metal? Solution: First we find the heat absorbed by the water, which is also the heat lost by the metal, then solve for the specific heat of the metal. q water = m water c water DT water = ( g) (4.184 J/g o C) ( o C o C) = J = q m c metal = q m m m DT m = J ( g)( o C o C) = 0. J/g o C. Specific Heats Item C (J/g o C) Air 1.01 Aluminum Copper Gold Iron steel 0.45 Brass.38 titanium.52 Water 4.18 Write a one page typed report that summarizes the experiment, neatly hand write your calculation including calculations, and comment on your result: 4

5 Name Period energy lab 2 potato chip calorimetry 20 Points due next class In this experiment we will assemble a calorimeter, then use it to burn a snack chip and see how many Nutritional Calories of heat it produces using the formula Q = mcdt. Note that 4,184 joules = 1 Nutritional Calorie (Q = heat in joules, m = mass in grams, c = specific heat in joules per gram per degree Celsius, DT = change in Celsius temperature Rules: Each group of 2 or less gets 1 sheet of aluminum foil and one piece of copper. One point deduction for each additional piece of either. 5 point deduction if not performed safely. Always ask permission before lighting a match. Digital thermometers available adjacent to hood. Must perform reaction in front of hood. 1. Listed procedure 2. Observations 3. Nutritional Calories Calculation Here is the design of an industrial calorimeter. Note that, like the specific heat experimental design, virtually all of the heat is transferred to the water, leading to very precise results. An example of a student-made calorimeter 4. Suggest three improvements to your calorimeter design. Note that this calorimeter, like a combustion engine, requires gas intake and product gas exhaust 4. Percent accuracy calculation Percent accuracy= measured chip calories/actual chip calories x 100 5

6 Name Period specific heat problem set 5 points each Show your work clearly and circle your answer for credit. Please be sure to include the units in your calculation. 1. A g chunk of metal at 92 degrees Celsius is placed in g of water (specific heat = joules/gram degree Celsius) at 25 degrees Celsius, warming it to 42 degrees Celsius. What is the specific heat of the metal? 2. A g chunk of metal at 95 degrees Celsius is placed in g of water at 25.0 degrees Celsius, warming it to 29.4 degrees Celsius. What is the specific heat of the metal? ml of ethanol (density = 0.7 g/ml) at 71 degrees Celsius is placed in g of water at 25 degrees Celsius, warming it to 34 degrees Celsius. What is the specific heat of the ethanol based on this data? 4. A student burns a potato chip, and finds that it can heat 45 ml of water (density 1.00 g/ml) from 25 to 75 degrees Celsius. If the package claims that each chip contains 8 nutritional calories, what is the percent accuracy of the measured chip calories? Note that 4,184 joules = 1 Nutritional Calorie. 6

7 Name How much did it cost to take a shower this morning? Please answer as organized as possible based on the following real data: 10 minute shower Water flow 6 gallons per minute Water heated from 25 to 75 degrees Celsius Specific heat of water is j/g O C Water heated electrically, cost is 10cents per kilowatt hour (kwh) 3,600,000 J = 1 kwh Lets assume 50% heat loss for warming pipes, hot water heating efficiency, etc. Hint: use q = mcdt to get joules then convert to kwh then cents; don t forget to factor in the 50% heat loss. I d like to see a nice organized answer for credit. Use pencil, and erase and rewrite where necessary. 7

8 welcome to planet earth. deluxe meals: please choose your primary energy source #1 #2 #3 #4 #5 energy unit 12 cost (to the planet): coal chemical reaction: specials: chemical reaction: value menu chemical reaction: oil Nuclear fission 235 U + 1 n 236 U 140 Xe + 94 Sr + 11 n Natural gas biomass all hydrocarbon based: C, H CO 2 + H 2 O Nuclear fusion 3 H + 1 H 4 He wood would you like to learn more about nuclear fusion? $$high Medium? All items $1 none wave wind solar geothermal hydro place your order: 1 8

9 welcome to planet earth please choose your eco-friendly vehicle ford model T toyota prius chevy volt honda civic gx appearance (1-10) fuel gas or ethanol gas 2012: plug-in hybrid, electric Electric or gas CH 4 availability used only (!) Now; >1 million sold now; now cost $850 (1909) 30K 40k 30k overall (1-10) please rate from 1-10: tesla 3 honda fcx clarity Google flying car bird electric scooter appearance (1-10) fuel electric 2 H 2? Electric availability 2017? Limited; 200 leased never laying around cost 35k 40k Not for sale a few bucks an hour Overall (1-10) Also: my eco-friendly car choice: E-85 fuel biodiesel flex fuel nissan leaf 9

10 energy and weight loss 2,000 an average diet is about nutritional calories per day 1,500 People burn roughly nutritional calories per day without exercise 3,500 one pound of body fat contains nutritional calories 1,000 one hour of intense cardio exercise burns nutritional calories 500 iif I eat normal, and run hard one hour per day I should lose nutritional calories per day 1 and I can expect to lose pound(s) per week. 10

11 how can we measure energy? by temperature change. For 1 L of water each o C tiny 4184 = joule (j) = 1000 calories (c) 4 = British Thermal Units (btu) = 1 Nutritional Calories (C) = kilowatt hours (kwh) huge 4,184,000 joules 1.16 Kilowatt hours 1,000,000 calories 1000 Nutritional Calories 3960 btu 11

12 specific heat heat Q = mcdt Mass (g) The amount of heat necessary to heat one g of water by one O C. Temp. change o C c = Specific heat constant = j/g o C for water how many joules of heat are needed to heat one cup (237 ml) of water from room temp. (25 o C) to boiling (100 o C)? Q = mcdt = (237)(4.184)(75) = 74,371 joules 7 12

13 forensic usefulness of specific heat please try the following problems remember: q = mcdt mass of metal (g) temp. increase ( o C) heat absorbed (J) what metal is it? Strontium Barium Magnesium 8 13

14 9 enthalpy = heat change at constant pressure DH = DH or DH rxn DH vs. q? DH = q when pressure is constant Q exothermic reactions DH is negative - endothermic reactions DH is positive + 14

15 standard enthalpies of vaporization and fusion. for water: H 2 O (l) H 2 O (g) DH o vap = 2260 j/g H 2 O (s) H 2 O (l) DH o fus = 334 j/g gas 2260 J/g DH vap DH cond J/g liquid 334 J/g DH fus DH solid -334J/g 10 solid 15

16 how many Nutritional Calories are required to heat 18 g of water from -20 to 110 o C? consider what happens as it heats up: First, it heats up from -20 to 0 o C q = mcdt = ( 18 )( 2.03)( 20 ) = 731 J Then, it melts at 0 O C: q = J/g 334 x g 18 = J Then it heats up from 0 to 100 O C: 7524 q = mcdt = ( 18 )( 4.18 )( 100 ) = J Then, it boils at 10O O C: q = 2260 J/g x 18 g = Finally, the steam heats up from 100 to 110 O C (assuming it can pressurize) q = mcdt = ( 18 )( 2.01)( 10 ) = J Total: 55,308 J compare to Nutritional Calories (C): J x 1 Nutritional Calorie = 4,184 J 58, energy and water Nut. Cal.: 6012 J J water energy C ice = 2.03 J/g O C C water(l) = 4.18 J/g O C C steam = 2.01 J/g O C melting: 334 J/g boiling: 2260 J/g 4184 Joules = 1 Nut. Cal. 16

17 free energy DG =DH-TDS josiah gibbs new haven Gibb s Free Energy (j) Enthalpy (j) Entropy (j/k) if DG < 0 we have a spontaneous process what is entropy?? 17

18 entropy = randomness DS = positive = more random liquid gas + more random liquid solid - less random 1 particle 2 particles + more random The big bang 18

19 for a reaction: DH=145,000 J DS = 322 j/k T= 382K is it spontaneous? (Apply DG =DH-TDS) DG =DH-TDS =145, (322) = 22,000 predicting spontaneous reactions positive: nonspontaneous. 19

20 DH spontaneity DS spontaneous? always never Rarely. Depends on T Usually Depends on T 20

21 bond energies it takes energy to break bonds bond energy (KJ/mol) H-H: 436 O=O: 498 H-O: 464 Q. how can we use this data to predict the energy output from burning hydrogen? A. Add up bond energies Predict the molar energy required or released for this draw molecules reaction: with bonds: 2 H 2 + O 2 2 H 2 O H-H H-H O=O H-O-H H-O-H 436 KJ 436 KJ 498KJ -464 KJ -464 KJ -464 KJ -464 KJ add up energies: Energy released: 486 KJ releases burning 4 grams of hydrogen Kilojoules 486 of energy; since 4.18 kilojoules = 1 nutritional calorie, this is about the same amount of energy 1 in cans of coca cola (100 Nutritional Calories) 21

22 Name Period Many people, including scientists, believe the Earth, and the people on it, are in trouble. Problems include global warming, air, land, and water pollution, ozone depletion, overpopulation, and urban sprawl, among others. People may disagree as to how serious these issues are, but most would agree that many of the problems relate to energy use. Here we will consider what energy is, how we use it, and how we measure it. Energy is defined as the ability to do work or produce heat. Our primary sources of energy are the combustion of fossil fuels, nuclear fission, and more passive sources including solar, wind, and geothermal energy. Currently, fossil fuels and the nuclear fission of uranium-235 provide most of our energy needs. In Connecticut, about 50% of our electrical energy comes from nuclear fission, 40% from burning oil, gas, biomass, and coal, and the rest is from solar, wind, geothermal, and other sources. 1 Nutritional Calorie = 4 BTU (British Thermal Units) = 1000 calories = 4184 joules = KWH Use this information above to answer the following questions 1. What is the primary source of energy that powers your rechargeable ipod? a. The battery b. The electrical outlet c. Sunlight d. Power Plants e. Power lines 2. What is the primary source of energy that heats this school? a. Power lines b. Oil c. Natural Gas d. Nuclear energy d. Solar energy e. Radiators 3. What is the primary source of energy that heat our Bunsen burners in class? a. gasoline b. propane c. natural gas d. power plants e. The gas jets 4. Electrical energy in Connecticut comes from a. Electrical outlets b. Power lines c. Nuclear power d. Nuclear power and combustion e. solar energy 5. What is energy? 6. What do you believe is the primary cause of global warming? energy ws12.1 energy: sources, definitions, and conversions Energy is measured using a variety of units. A Nutritional Calorie is one most of us are familiar with. Not to be confused with the scientific calorie, (note the small c), a Nutritional Calorie is the amount of energy required to raise the temperature of a liter of water by one degree Celsius. Unfortunately, lots of different energy units are used, so we need to be familiar with them and know how to convert them. Here are the most common ones: 7. How much energy is required to heat a liter of water from 25 O C to 27 O C? Please show your calculation including cancelled units. (use q = mcdt) 8. You just ate a chocolate bar, which will provide your body with 300 Nutritional Calories of sugar-rush energy. Please show your calculation below including cancelled units. Convert this 300 Nutritional Calories to a. Joules (Hint: there are 4184 joules in a Nutritional Calorie): b. British Thermal Units (btu): c. kilowatt hours (kwh): 22

23 Name Period specific heat worksheet energy ws12.2 Have you ever noticed how some substances feel colder than others in a room? Or have you noticed that some metals like iron retain their heat for a long time, while others like aluminum cool very quickly? Clearly, substances vary in their responses to heating and cooling. The amount of energy needed to heat a substance is known as specific heat, and is unique for each pure substance. The units are j/g O C, which literally means the amount of energy in joules needed to raise the temperature of one gram of the substance one degree Celsius. Liquid water requires over joules, while gold only requires about 1/10 of a joule for each gram to get one degree Celsius hotter. All of these problems may be solved using the specific heat equation: q = mcdt where q = heat in joules m= the mass of the substance in g c = the specific heat of the substance in j/g o C (2.03 for ice, for liquid water, and 2.01 for steam) And DT is the absolute temperature change in o C. Example: How much energy must be absorbed by 20.0 g of liquid water (C water = j/g 0 C) to increase its temperature from C to C? Solution: q = mcdt Use the specific heat = formula (20.0 g)(4.184 below to J/g learn 0 C)(20 about o C) the = thermal 1,673.6 properties J of various substances. The first problem is solved for you. The answers are given; you must show the work to get there. 1. When 15.0 g of steam drops in temperature from C to C, how much heat energy is released? 2. How much energy is required to heat g of water from C to C? (754 J) 3. If g of steam at C absorbs joules of heat energy, what will be its increase in temperature? (11,046 J) (0.55 O C) 23

24 4. How much heat (in J) is given out when 85.0 g of lead cools from C to 10.0 C? (C lead = J/g C) 5. If it takes joules to heat a piece of gold weighing g from 10.0 C to 27.0 C, what is the specific heat of the gold? (2080 J) 6. If 35 g of a substance absorbs 4000 J of heat when the temperature rises from 25 to C, what is the specific heat of that substance? (0.131 J/g O C) 7. A certain mass of water was heated with 41,840 Joules, raising its temperature from 22.0 C to 28.5 C. Find the mass of water (0.235 J/g O C). 8. Calculate the number of joules given off when 32.0 grams of steam cools from 90 degrees Celsius to 31 degrees Celsius. (1540 g) 9. How many joules of heat are lost by 3580 kilograms of granite as it cools from 41.2 O C to O C? The specific heat of granite is J/g O C (3800 J) (1.56 x 10 8 J) 10. In reality we are making a lot of assumptions for these calculations to be accurate. For example, in many cases we are assuming a perfectly insulated container. List two other assumptions we are making in these calculations

25 Name Period energy ws3 In the previous worksheet we learned to use the specific heat equation: energy of heating and cooling water q = mcdt Where q = joules of heat, m = grams of mass, c = specific heat in j/g O C, and DT = degrees of temperature change, To heat or cool water we have to consider the phase it is in, as well as the energy associated with phase changes. Heating water may sound simple enough, but consider a block of ice, and think about what happens as it heats: 1. The ice warms to 0 O C 2. The ice melts at 0 O C 3. The water heats to 100 O C 4. The water boils at 100 O C. 5. The steam raises to it s final temperature. Note for the last step we assume a closed system that would pressurize. The specific heat for each phase, and the energy required at constant pressure (called enthalpy) for each temperature change is summarized below. Symbol and value Symbol What it means c water(l) = 4.18 J/g o C The specific heat of liquid water It takes 4.18 joules of heat energy to raise the temperature of 1 gram of liquid water by one degree Celsius c water(s) = 2.03 J/g o C The specific heat of ice It takes 2.03 joules of heat energy to raise the temperature of 1 gram of solid water (ice) by one degree Celsius c water(g) = 2.01 J/g o C The specific heat of steam It takes 2.01 joules of heat energy to raise the temperature of 1 gram of gaseous water (steam) by one degree Celsius DH vap = 2,259 J/g The enthalpy of vaporization of water It takes 2,259 joules of energy to boil one gram of liquid water (convert it from a liquid to a gas). DH fus =334 J/g The enthalpy of fusion of water It takes 334 joules of energy to melt one gram of liquid water (convert it from a solid to a liquid). Use these ideas to answer the guided questions on the next page. 25

26 water energy calculations 1) A 12 oz. bottle of water 450 g of water. How many joules are released when it is placed in your refrigerator, where it cools from 25 degrees Celsius (room temperature) to 4 degrees Celsius? Hint: q=mcdt; The specific heat of liquid water is 4.18 J / gram x o C 2) How many joules are required to heat 250 grams of liquid water from 0 0 to C? Hint: q=mcdt (39.5kJ, or 39,500 J) (104.5 kj) 3) How many joules are required to melt 100 grams of water? (33.4 kj) 4) How many joules are required to boil 150 grams of water? (338.8 kj) 5) How many joules are required to heat 200 grams of water from 25 0 C to C? The specific heat of steam is 2.01 J / g. 0 C (Hint: there are 3 parts to this) Hint: Here are the parts Part 1: C: q = mcdt = ( )( )( )= Part 2: boiling at 100 o C: 40,670J/mole. moles = Part 3: C: q = mcdt = ( )( )( ) = Total = = (524.7 kj) 6. How much heat is required to warm 225 g of ice from C to 0.0 C, melt the ice, warm the water from 0.0 C to C, boil the water, and heat the steam to C? 26

27 7. How much energy is required to heat a liter of water from 25 O C to 27 O C? Please show your calculation including cancelled units. (use q = mcdt) 8. You just ate a chocolate bar, which will provide your body with 300 Nutritional Calories of sugar-rush energy. Please show your calculation below including cancelled units. Convert this 300 Nutritional Calories to a. Joules (Hint: there are 4184 joules in a Nutritional Calorie): b. British Thermal Units (btu): c. kilowatt hours (kwh): 9. Here is some information that one consumer considered before purchasing a hybrid vehicle: My gas-powered Nissan gets 30 miles per gallon (that s 30 miles/gallon), and gas currently costs $4.00 per gallon. a. How much does it cost to drive my Nissan one mile? Each mile driven by a Toyota Prius uses 0.25 kilowatt hours of electrical energy when the combustion engine is off (that s 1 mile/0.253 kwh) and the electricity costs 10 cents per kwh. b. How much does it cost to drive the Prius one mile? c. Which is cheaper to drive- the Nissan, or the Toyota Prius? And how much cheaper is it? 10 (L1 only). Assuming I drive 20,000 miles per year, and the Prius costs 10,000 dollars more than the Nissan, how long will it be before the Prius actually starts saving me money? 27

28 Names (maximum of 2) Period Ethylene glycol (HOCH 2 CH 2 OH) is used as a radiator fluid in gasoline engines. Use the data in the attached material safety data sheet to calculate the energy required to heat one gallon (4,214 grams) of ethylene glycol from -220 degrees Celsius to +220 degrees Celsius. Here is the data you need for ethylene glycol (note that the solid and gas specific heat data are estimates) Melting point -13 degrees Celsius Boiling poing: 197 degrees Celsius Specific heat of ethylene glycol Solid: 1.2j/g O C Liquid: 2.39 j/g O C Gas: 1.3 j/g O C DH fus : joules/g DH vap : 1058 joules/g Step (indicate what is happening- the temp. change or phase change( Formula (either Q = mcdt) or DH fus or DH vap ) Just the formula, plug in on the next5 column plug in (show your calculation with cancelled units) Total (joules) 1: 2: 3: 4: 5: total: 28

29 The function of a radiator in an automobile is to keep the engine from getting too hot. If the radiator fluid freezes it will crack the radiator, and if it boils the it will overpressurize and blow off the cap. So the ideal radiator fluid has a very high liquid range, so it is unlikely to freeze on the coldest winter day, or boil on the hottest summer day. It also helps if the radiator fluid can absorb as much heat as possible. This goal is to keep the size of the radiator as small as possible to save weight, volume, and cost, which helps fuel efficiency and cost. Older vehicles used to use water as a radiator fluid, they now use ethylene glycol as an additive. What are the advantages and disadvantages of using ethylene glycol in an automobile radiator. Consider the liquid range of each, the specific heat of each, likely costs, and any other criteria you may need. Three paragraph minimum, no maximum. 5 points each for neatness, length, and accuracy. 29

30 Name Period energyws12.4 Where DG = DH TDS DG = Gibbs Free Energy DH = Enthalpy in Joules T = Temperature (K) And DS = Entropy in Joules/K free energy worksheet We have just learned that if the free energy (DG) of a reaction is negative, that reaction will occur spontaneously. This can be calculated using the Gibbs Free Energy Equation shown on the left, named after New Haven s own J. Willard Gibbs. Now, usually a reaction is spontaneous if it is exothermic. Bang. Occasionally, Example: Calculate DG and indicate if the reaction is spontaneous when DH = 2.3 kj, T = 25 O C, and DS = 195 J/K however, an endothermic reaction can be spontaneous. The melting of ice is a good example. DH is slightly positive, but it has something else going for it: the process produces disorder. This provides enough boost to make the reaction spontaneous at room temperature. This randomness factor is called entropy (S). Examples of increased randomness include a liquid becoming a gas, something splitting in two, or things spreading out, like the expansion of the universe. As Entropy increases it becomes more positive. If we know the temperature, enthalpy, and entropy of a reaction or system we can use the Gibbs Free energy equation to predict if the reaction will be spontaneous. Solution: Note that we need to convert kilojoules (kj) to joules (1000 J = 1 kj), and degrees Celsius to Kelvin (K = O C + 273). DG = DH-TDS = 2300 J (298 K. 195 J/K) = -55,810 J = spontaneous Most common errors: Did not change kj to J; did not change O C to K; subtracting before multiplying. Calculate DG and indicate if the process is spontaneous or nonspontaneous 1. DH = 145 kj, T = 293K, DS = 195 J/K 2. DH = -232 kj, T = 273K, DS = 138 J/K 3. DH = kj, T = 100 o C, DS = -268 J/K 4. Calculate the temperature at which DG = 34.7 kj if DH = 40.2 kj and DS = 22.2 J/K. 5. Iron ore can be converted to iron by the following reaction: Fe 3 O 4 (s) + 4H 2 (g) 3Fe(s) + 4H 2 O(g) DH = kj For this reaction DS = 610 J/K.. Is this reaction spontaneous at 298K? What is the value of DG? 30

31 review energy: what changes should we make? How to ace the Energy exam In this our 12 th unit we investigated Energy, both from a scientific and environmental perspective. We began by considering the primary sources of energy we use, and their environmental consequences, as well as their abundance. This is perhaps the most important information needed to answer our essential question for this unit: We looked at some efforts to answer this question in the form of transportation when we took a look at some eco-friendly cars. We then focused on the hard science that relates to energy: what it is, types of energy, Enthalpy, and exothermic and endothermic chemical reactions. During this time we performed two experiments where we measured the specific heat of an unknown metal, and the energy contained in a potato chip, using a calorimeter of our own design. We finished by considering the energy required to heat water, including the phase changes that may be involved, and we familiarized ourselves with Free energy, which includes the esoteric concept of entropy. To ace this unit be familiar with the terminology associated with energy, know how to measure it, and think about the sources of energy we use, and what changes we must make for the sake of our planet. As usual, review your notes, worksheets, and lab experiments, and answer all of the questions below. In our next unit we will ask why some reactions such as explosions are rapid, while others such as rust are slow- this is our Rates of Reaction unit, coming up. Useful information to be provided on test: q = mcdt where m = mass (g), c = specific heat (J/g 0 C; see examples for H 2 O below), and DT = change in temperature ( 0 C) c water(l) = 4.18 J/g o C c water(s) = 2.03 J/g o C c water(g) = 2.01 J/g o C DH vap = 2260 J/g DH fus = 334 J/g At 1 atm: Water boils/condenses at 100 o C Water melts/freezes at 0 o C 1 Nutritional Calorie = 4 BTU (British Thermal Units) = 1000 calories = 4184 joules = KWH DG = DH-TDS Where DG = change in free energy (J), DH = change in enthalpy (J), T = temperature (K), and DS = change in entropy (J/K) Energy Enthalpy (DH) Exothermic Endothermic Specific Heat Heat of vaporization (DH vap ) Heat of fusion (DH fus ) wordly wise Know the meaning of these terms Heat of condensation (DH cond ) Heat of solidification (DH solid ) calorie Nutritional Calorie Joule Free Energy Entropy 31

32 Please answer the following questions to prepare for the energy test. You should also review the experiments, slides, and worksheets. 1. Arrange from the lowest amount (1) to largest amount (5) 1 calorie 1 Nutritional Calorie 1 BTU 1 joule 1 kilowatt hour 2. By placing a hot chunk of metal into water in a well insulated container (a calorimeter) one can find the specific heat of the metal. Please do that using this data: Mass of metal = 8.3 g Initial temp of metal = 74.5 O C Final temp of metal = 31.0 O C Mass of water= 25.0 g Initial temp of water= 25.3 O C Final temp of water= 31.0 O C Specific heat of water = J/g O C 3. A 0.83 g potato chip is burned in a calorimeter, raising the temp of 27.3 g of water from 24 to 71.2 O C. Assuming perfect heat transfer, how many nutritional calories are in that potato chip? The specific heat of water is Nutritional Cal/g O C. 4. Which power plants create CO 2 as a reaction product? Coal nuclear fission wind solar natural gas biomass combustion geothermal hydroelectric wave energy ethanol combustion nuclear fusion 5. What is E-85 fuel? How does a plug-in hybrid car function, and what inherent advantages does it offer? 6. What is the difference between a nuclear and a chemical process? 7. Given the data below for a chemical reaction, will it happen spontaneously as soon as the reactants are combined? DH = 145 KJ DS = 322 J/K T = 340 O 8. What is the nuclear reaction in current experimental nuclear fusion power plants? + Why is this process considered relatively safe? Why is there an inexhaustible supply of the fuel needed? Why is this process challenging? 9. If 450 g of steam absorbs 15 KJ of energy, how much hotter did it get? 10. If 712 g of steam at 127 O C is cooled to a -12 O C block of ice, how much energy is released? (answer on a separate sheet of paper). 11. Methanol has a density of g/ml, with the following specific heats in J/g O C: solid: 2.47 liquid: 2.51 gas Boiling point 65 degrees Celsius, melting point -98 degrees Celsius. Calculate the energy needed to heat 250 ml of methanol from -250 to +250 degreed Celsius. Use a separate sheet of paper. 32

33 For the energy unit, instead of taking a test, each student will write a test. Due: Friday, May 22 Write five relatively challenging multiple choice and five short answer questions using powerpoint. 4 points for each unique question and 4 points for each correctly solved answer showing any work needed for a maximum of up to 80 points. Submit a hard copy and me your digital copy (brielmannh@guilfordschools.org). See the checklist below for specific requirements. So that I can use these questions as a test bank in future years, please use the sample questions below as templates. Make the questions interesting! Please include all topics covered in the unit. Please refer to the checklist at the bottom for specific requirements, this will be used in scoring. Here is a sample short answer question and answer: use this as a template for your own questions. 3,959.4 J 1. How much energy is needed to heat 10.0 g of (H 2 O) from degrees Celsius to degrees Celsius? Please show your work below for credit. Solution: 1. The water is heated from -10 to 0 degrees Celsius: Q = mcdt = (10.0 g) (2.03J) (10 o C) = J g O C 2. The water melts: 334 J x 10 g = 3,340 J g 3. The water heats from 0 to +10 degrees Celsius: Q = mcdt = (10.0 g)(4.184 J)(10 o C) = J g O C Total: 3,959.4 J Here is a sample multiple choice question: B 1. Which of the following is true about a nuclear fission power plant? a. The fuel used is hydrogen b. One of the major issues is that it creates radioactive waste c. It uses a renewable fuel source d. They are experimental only thus far, though commercial plants may appear in the near future Solution: a. The fuel used is hydrogen: no, that is for nuclear fusion b. One of the major issues is that it creates radioactive waste: true, and it is a big problem c. It uses a renewable fuel source: no, once we are out of uranium it is forever. d. They are experimental only thus far, though commercial plants may appear in the near future: no, that is for nuclear fusion. Checklist 1. 5 unique multiple choice questions, and 5 short answer questions that are interesting, challenging, and properly formatted using powerpoint (use the sample questions as templates). 2. Each question is solved in detail using the sample questions as a guide. Note the cancelled units, horizontal lines, and color coding- use the same level of detail. 3. All topics covered: specific heat, weight loss, enthalpy, entropy, free energy, phase changes, power sources 4. Hard copy handed in and digital copy ed to Dr B by May 22 33