Evaluation copy. Energy Content of Fuels. computer OBJECTIVES MATERIALS

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1 Energy Content of Fuels Computer 24 is an important property of fuels. This property helps scientists and engineers determine the usefulness of a fuel. is the amount of heat produced by the burning of 1 gram of a substance, and is measured in joules per gram. You can determine energy content of a fuel by burning an amount of the fuel and capturing the heat released in a known mass of water in a calorimeter. If you measure the initial and final temperatures, the energy released can be calculated using the equation H = t m C p where H = heat energy absorbed (in J), t = change in temperature (in C), m = mass (in g), and C p = specific heat capacity (4.18 J/g C for water). Dividing the resulting energy value by grams of food burned gives the energy content (in J/g). OBJECTIVES In this experiment, you will Use a computer to measure temperature. Use a computer to analyze data. Use a balance. Determine energy content. Compare the energy content of different fuels. MATERIALS computer Vernier computer interface Logger Pro Vernier Temperature Probe fuel sample (candle, oil, or alcohol) ring stand and 10 cm (4") ring utility clamp slit stopper 100 ml graduated cylinder 2 stirring rods balance small can cold water matches Evaluation copy Figure 1 Agricultural Science with Vernier 24-1

2 Computer 24 PROCEDURE 1. Obtain and wear goggles. 2. Connect the probe to the computer interface. Prepare the computer for data collection by opening the file 24 Energy of Fuels from the Agricultural Science with Vernier folder. 3. Find and record the initial mass of the fuel sample assigned to you. 4. Set up the apparatus shown in Figure 1. a. Determine and record the mass of the empty can. b. Place cold water from the teacher into the can. Use 100 ml of water. Weight the can and the water. c. Record the mass of the can plus water. d. Use a 10 cm ring and stirring rod to suspend the can about 5 cm above the candle or lamp. e. Use a utility clamp and slit stopper to suspend the Temperature Probe in the water. The probe should not touch the bottom of the can. 5. Click to begin measuring temperature. Remember: The Temperature Probe must be in the water for at least 45 seconds before you begin! After 3 or 4 temperature readings have been made, light the fuel. Record the initial temperature. Heat the water until its temperature reaches 40 C and then extinguish the flame. CAUTION: Keep hair and clothing away from open flames. 6. Stir the water until the temperature stops rising. Record this final temperature. Click to end data collection. 7. Determine the final mass of the fuel used. 8. To confirm the initial temperature, examine the initial data points in the table. To confirm the final temperature, click the on the graph to select it and then click the Statistics button,. The maximum temperature is listed in the statistics box on the graph. 9. Repeat the procedure 2 time more using the same fuel. Start with cold water again Agricultural Science with Vernier

3 Energy Content of Fuels DATA Trial 1 Trial 2 Trial 3 Fuel used Mass of fuel (initial) (g) Mass of fuel (final) (g) Mass of empty can (g) Mass of can plus water (g) Initial water temperature ( C) Final water temperature ( C) PROCESSING THE DATA 1. Calculate the change in water temperature, t, for each sample by subtracting the initial temperature from the final temperature ( t = t final t initial ). 2. Calculate the mass (in g) of the water heated for each sample. Subtract the mass of the empty can from the mass of the can plus water. 3. Use the results of Steps 1 and 2 to determine the heat energy gained by the water (in J). Use the equation H = t m C p where H = heat absorbed (in J), t = change in temperature (in C), m = mass of the water heated (in g), and C p = specific heat capacity (4.18 J/g C for water). 4. Calculate the mass (in g) of fuel burned. Subtract the final mass from the initial mass. 5. Use the results of Steps 3 and 4 to calculate the energy content (in J/g) of the fuel samples. Agricultural Science with Vernier 24-3

4 Computer Record your results and the results of other groups in the Class Results table below. Class Results Fuel Type Fuel Type Fuel Type Fuel Type Average: Average: Average: Average: 7. Which of the fuels has the greatest energy content? 8. List two other factors, in addition to energy content, that might be important in choosing a fuel. EXTENSIONS 1. Make a bar graph comparing the fuels tested in your class. 2. Design an experiment to compare heat content of different alcohols or oils. Post lab questions: 1) On a food label, there are 3 major macronutrients. What are they and what are their Calories per gram? 2) Nuts are considered nutrient rich foods. What do we mean when we say "nutrient rich"? 3) Different nuts like one's we tested are a good fuel source for burning or starting fires. What chemical component in nuts helps these fuels burn easily and produce as much heat as they do? 24-4 Agricultural Science with Vernier

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