* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download SPECIFIC HEAT
Survey
Document related concepts
Passive solar building design wikipedia , lookup
Water heating wikipedia , lookup
Space Shuttle thermal protection system wikipedia , lookup
Thermal conductivity wikipedia , lookup
Dynamic insulation wikipedia , lookup
Building insulation materials wikipedia , lookup
Heat exchanger wikipedia , lookup
Thermoregulation wikipedia , lookup
Solar air conditioning wikipedia , lookup
Intercooler wikipedia , lookup
Solar water heating wikipedia , lookup
R-value (insulation) wikipedia , lookup
Cogeneration wikipedia , lookup
Copper in heat exchangers wikipedia , lookup
Heat equation wikipedia , lookup
Transcript
CALORIMETRY & SPECIFIC HEAT THEORY Heat energy is defined as energy that flows from hot objects to cold objects. It can be measured in calories, kilocalories, or joules of energy. One calorie is defined as the amount of heat required to raise the temperature of 1 gram of water by 1 C. One calorie is equivalent to 4.184 joules. Different substances of identical mass require different amount of heat to raise their temperatures a certain degree. A specimen's heat capacity is C Q , T where Q = amount of heat added or subtracted from the specimen, and T = temperature change of the specimen. The specific heat capacity of the specimen's substance is c C Q , m mT where m = mass of the specimen. Thus, the amount of heat gained by a specimen is given by Q = mcT. A calorimeter can measure c for a specimen by the method of mixtures. A specimen of known mass m is combined with water of known mass mw and specific heat capacity cw, inside a calorimeter. Ideally, the cup is insulated such that no heat is lost or absorbed by it. The heat lost by the specimen, Qs, is gained by the water as Qw. Qs = Qw mscsTs = mwcwTw. To keep the heat flow values Qs and Qw positive, use the absolute value of the specimen's temperature change T [express T as (Ti – Tf) to get a positive value]. Work with your lab partner to derive an expression for the specific heat capacity of the metal. Show your instructor what you come up with. Do not plug in values until the very end. PURPOSE Test whether your derived expression for specific heat capacity predicts the accepted value of c for the sample. By experimentally determining c using equation and comparing this to the accepted value of c, the theory behind calorimetry and the method of mixtures is tested. 1 SETUP Use the Styrofoam cups, supplied beakers, and electric hot plate provided. PROCEDURE Heat the sample in a beaker of boiling water. Transfer to room temperature water in the calorimeter cup. Take data using the PASCO temperature sensors during the entire time and produce a graph of the entire process. Analyze your graph to determine the initial temperatures of the sample and water and final temperatures of the sample and water. SOURCES OF ERROR Take careful care during the data gathering process to be sure your data is valid. Do not rest the specimin and/or the thermometers on the bottom and/or against the sides of the beaker. Stir the water in your beaker continuesly. Allow enough time for thermal equilibrium to be reached and for the data curves to flatten out. Check your lab partners work. Have the instructor check your work before tearing down and/or moving on to new things. ANALYSIS Calculate c for your unknown sample and compare to theory. Be sure to include the percent difference of your experimental results as compared to theory in your conclusion. The following are the accepted values of c for different elements, measured at 25 C: caluminum = 897. JkgC, clead = 195. JkgC, ccopper = 385. JkgC, ctin = 523. JkgC, and czinc = 388. JkgC. STATISTICAL CONSIDERATIONS (OPTIONAL): 1. Calculate c for each of the four runs. Tabulate c for each run n = 1 to 4. 2. Compute c = mean of c. 3. Compute sc = standard deviation of c. 4. Calculate x - k, x + k = the interval that includes the parent mean (the true mean) with a 100(1 - ) percent confidence. Take = .05 for a 95% confidence. Use the critical value t formula and the t-distribution table, s k t 2 n-1 1 2 = .975 0 5. 1 12.706 c n 2 4.303 3 3.182 4 2.776 9 2.262 Determine whether the accepted value of c falls within this 95% confidence interval. If it does not, calculate the percent difference of the theoretical result from the given value. REFERENCES CRC Handbook of Chemistry and Physics, 75th edition, David R. Lide (editor), 1994, CRC press, Incorporated, Boca Raton, Florida. 2