When two samples of matter that are initially at different temperatures are placed in thermal contact, the samples undergo heat transfer until reaching thermal equilibrium at some new, final temperature. Transferred heat (q) can be measured based on the initial and final temperatures (Tinitial and Tfinal) of a sample that is placed into a known volume of water inside the insulated chamber of a calorimeter.Figure 1 Analysis of a heated sample using a calorimeterAccording to the first law of thermodynamics, the transferred heat energy is conserved, and the heat lost from the sample (indicated by a negative sign) must be equal to the sum of the heat gained by the water and the calorimeter, as expressed by Equation 1.−qsample = qwater + qcalorimeterEquation 1In a perfectly efficient system, qcalorimeter = 0, and all the heat released from the sample is retained by the water. In real systems, some heat is absorbed by the calorimeter itself. Based on the amount of heat transferred from the sample and the change in temperature, the heat capacity (C) of the entire sample can be determined. Expressing the heat capacity per unit mass yields the specific heat capacity (Cp) of the substance comprising the sample.Table 1 Measured specific heat capacities of several selected substancesSample Specific heatcapacity (J/g·°C)Lead 0.129Tungsten 0.132Silver 0.235Strontium 0.315Zinc 0.388Cobalt 0.421Titanium 0.525Wood 2.00Paraffin wax 2.5Water 4.184Experiment 1A sample of water (10.0 mL at 75 °C) was stirred into a calorimeter containing 100.0 mL of water initially at 21 °C. At thermal equilibrium, the system was found to have a temperature of 25 °C.Experiment 2The water in the calorimeter from Experiment 1 was discarded and replaced with 100.0 mL of fresh water at 25 °C. An unidentified 100.0 g sample of one of the metals from Table 1 was heated to an initial temperature of 80 °C and then placed into the water. At thermal equilibrium, the system was found to have a temperature of 30 °C. Question 58Based on the results of the calorimetry experiments, a lab technician concludes that the specific heat capacity of the unidentified metal sample is 0.42 J/g·°C. Is this conclusion correct?A.Yes; qwater ≈ qmetal in Experiment 2 because Experiment 1 shows that the heat lost from the water and absorbed by the calorimeter is negligible (qcalorimeter ≈ 0).B.Yes; qwater < qmetal in Experiment 2 because Experiment 1 shows that the sample absorbs a small amount of heat from the calorimeter (qcalorimeter < 0).C.No; qwater < qmetal in Experiment 2 because Experiment 1 shows that a significant amount of heat from a sample is lost from the water and absorbed by the calorimeter (qcalorimeter > 0).D.No; qwater > qmetal in Experiment 2 because Experiment 1 shows that the calorimeter adds a small amount of heat to the water (qcalorimeter < 0).
Question
When two samples of matter that are initially at different temperatures are placed in thermal contact, the samples undergo heat transfer until reaching thermal equilibrium at some new, final temperature. Transferred heat (q) can be measured based on the initial and final temperatures (Tinitial and Tfinal) of a sample that is placed into a known volume of water inside the insulated chamber of a calorimeter.Figure 1 Analysis of a heated sample using a calorimeterAccording to the first law of thermodynamics, the transferred heat energy is conserved, and the heat lost from the sample (indicated by a negative sign) must be equal to the sum of the heat gained by the water and the calorimeter, as expressed by Equation 1.−qsample = qwater + qcalorimeterEquation 1In a perfectly efficient system, qcalorimeter = 0, and all the heat released from the sample is retained by the water. In real systems, some heat is absorbed by the calorimeter itself. Based on the amount of heat transferred from the sample and the change in temperature, the heat capacity (C) of the entire sample can be determined. Expressing the heat capacity per unit mass yields the specific heat capacity (Cp) of the substance comprising the sample.Table 1 Measured specific heat capacities of several selected substancesSample Specific heatcapacity (J/g·°C)Lead 0.129Tungsten 0.132Silver 0.235Strontium 0.315Zinc 0.388Cobalt 0.421Titanium 0.525Wood 2.00Paraffin wax 2.5Water 4.184Experiment 1A sample of water (10.0 mL at 75 °C) was stirred into a calorimeter containing 100.0 mL of water initially at 21 °C. At thermal equilibrium, the system was found to have a temperature of 25 °C.Experiment 2The water in the calorimeter from Experiment 1 was discarded and replaced with 100.0 mL of fresh water at 25 °C. An unidentified 100.0 g sample of one of the metals from Table 1 was heated to an initial temperature of 80 °C and then placed into the water. At thermal equilibrium, the system was found to have a temperature of 30 °C. Question 58Based on the results of the calorimetry experiments, a lab technician concludes that the specific heat capacity of the unidentified metal sample is 0.42 J/g·°C. Is this conclusion correct?A.Yes; qwater ≈ qmetal in Experiment 2 because Experiment 1 shows that the heat lost from the water and absorbed by the calorimeter is negligible (qcalorimeter ≈ 0).B.Yes; qwater < qmetal in Experiment 2 because Experiment 1 shows that the sample absorbs a small amount of heat from the calorimeter (qcalorimeter < 0).C.No; qwater < qmetal in Experiment 2 because Experiment 1 shows that a significant amount of heat from a sample is lost from the water and absorbed by the calorimeter (qcalorimeter > 0).D.No; qwater > qmetal in Experiment 2 because Experiment 1 shows that the calorimeter adds a small amount of heat to the water (qcalorimeter < 0).
Solution
The correct answer is A. Yes; qwater ≈ qmetal in Experiment 2 because Experiment 1 shows that the heat lost from the water and absorbed by the calorimeter is negligible (qcalorimeter ≈ 0).
Here's why:
In Experiment 1, the water in the calorimeter started at 21°C and ended at 25°C after adding 10.0 mL of water at 75°C. This shows that the calorimeter does not absorb a significant amount of heat (qcalorimeter ≈ 0), as the final temperature is closer to the initial temperature of the water in the calorimeter than the added water.
In Experiment 2, the unidentified metal sample was heated to 80°C and then placed into the water at 25°C. The final temperature was 30°C. If the specific heat capacity of the metal was indeed 0.42 J/g·°C (as suggested by the lab technician), it would mean that the heat lost by the metal (qmetal) is approximately equal to the heat gained by the water (qwater). This is consistent with the first law of thermodynamics and the observations from Experiment 1.
Therefore, the conclusion of the lab technician seems to be correct.
Similar Questions
The heat associated with the reaction which happens in the calorimeter is calculated by:Question 4Select one:adding the heat absorbed by the calorimeter to the heat absorbed by the solutiontaking the heat absorbed by the solution, and then changing the signtaking the heat absorbed by the calorimeter and then changing the signadding the heat absorbed by the calorimeter to the heat absorbed by the solution, and then changing the sign
What does the law of conservation of energy say and how does this apply to the process of heat transfer that occurs in calorimetry?
Which device is used to measure the heat energy transferred in a physical or chemical process?Options:A) ThermometerB) CalorimeterC) HygrometerD) Barometer
To calculate the heat absorbed by the calorimeter you:Question 3Select one:multiply the calorimeter constant by the temperature change.multiply the mass of the solution by its specific heat capacity and by the temperature change. multiply the calorimeter constant by the mass of the calorimeter and by the temperature change.
How heat is transferred?*
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