CHM 113 POST-LAB Enthalpy and Specific Heat

CHM 113 POST-LAB Enthalpy and Specific Heat 1. Insert ONE picture of yourself in full PPE here (include the hot pad). **Remember to (1) show your full body so that we see you are wearing shoes; (2) wear your safety glasses, apron and gloves; (3) cover your arms and lower legs (socks are not optional, even in Arizona); (4) tie back long hair in a ponytail or a bun; (5) remove jewelry. 2. Complete the following table with your experimental data for the masses of the water and the unknown metal strip in Part 1. Table 1: Mass Data Mass (g) Trial 1 Trial 2 Trial 3 Water 48.8g 48.1g 49.8g Metal Strip 9.5g 9.6g 9.6g 3. Complete the following table with your experimental data for the temperature changes for the water in your calorimeter in Part 1, and calculate the temperature change (ΔT) for each trial. Show your work below the table and include units. ∆T =T final−T initial Table 2: Specific Heat Data Time (minutes) Temperature (°C) Trial 1 Trial 2 Trial 3 Initial 24.4 24.3 24.6 1 minute 25.7 26.1 28.7 2 minutes 25.2 25.6 27.0 3 minutes 25.0 25.3 26.2 4 minutes 24.8 25.2 25.9 5 minutes 24.8 25.1 25.7 ΔT 0.4 0.8 1.1 Calculations of ΔT Trial 1: 24.8 – 24.4 = 0.4 C Trial 2: 25.1 – 24.3 = 0.8 C Trial 3: 25.7 – 24.6 = 1.1 C 4. Calculate the specific heat (C or Cs) of the unknown metal strip for each trial here. What is the average specific heat for all three trials? Show your work and include units. Hint: Table 2 shows the change in the temperature for the water. For the change in temperature of your metal, consider the initial temperature of the metal (Part 1, Step 9 in Procedure 95.5, 96.7, 96.6) as well as the final temperature once the calorimeter contents reached equilibrium. qwater +qmetal =0 Calculations of Specific Heat Trial 1: qw = mCw ∆T qw = (48.8g)(4.184 J/goC)(0.4oC) qw =81.7J qw = -qm Cm = - qw / mm ∆Tm Cm = -81.7 J/ (9.5g (24.8 oC-95.5 oC)) Cm = 0.121J/ goC Trial 2: qw = mCw ∆T qw = (48.1g)(4.184 J/goC)(0.8oC) qw =161 J Cm = - qw / mm ∆Tm Cm = -161 J/ (9.6g (25.1 oC-96.7 oC)) Cm = 0.234J/ goC Trial 3: qw = mCw ∆T qw = (49.8g)(4.184 J/goC)(1.1oC) qw =229 J Cm = - qw / mm ∆Tm Cm = -229 J/ (9.6g (25.7 oC-96.6 oC)) Cm = 0.336 J/ goC Average Specific Heat: Cmetal avg = (0.234+0.336+0.121)/3 Cmetal avg =0.230 J/ goC 5. Putting it all together! Using the table of Specific Heat Capacities in the Pre-Lab Handout as well as the average specific heat capacity you calculated in Question 4, what is the identity of the unknown metal? Explain how you know. Based on the table of specific heat capacity of the metals shown, the unknown metal is most likely Tin, since it has the Specific heat capacity value of 0.213 J/ goC which was closest to my experimental value of calculated specific heat capacity of unknown metal which was 0.230 J/ goC. 6. Complete the following table with your experimental data for the cold pack and hand warmer experiments below. Highlight (in yellow) the minimum temperature for the cold pack and the maximum temperature for the hand warmer. Tables 3 & 4 Cold Pack Hand Warmer Time (sec) Temperature (°C) Temperature (°C) Initial 24.2 25.9 30 21.1 31.3 60 19.9 34.1 90 19.3 36.8 120 18.2 39.5 150 17.4 41.2 180 16.9 42.2 210 16.3 44.4 240 15.7 44.2 270 15.3 43.9 300 14.9 43.4 330 14.8 43.1 360 390 420 450 7. Plot your data from Tables 3 and 4 (TWO data sets from Question 6) on one x-y scatter plot using a graphing program. Your graph should show the temperature as a function of time. You will not receive credit if you draw your graph by hand. Excel or Google Sheets are good choices that you can learn how to use quickly if you don’t already have a favorite graphing program. On your graph, the x-axis should be the time (in seconds), and the y-axis should be the temperature (in °C) at that temperature. Make sure to label the axes including the units in parentheses but REMOVE the chart title and any default legend put in by the graphing software. In the figure legend (text below the graph), explain the data in your graph. Be sure to use different symbols (and make them different colors) for the two data sets and mark the maximum (hand warmer) and minimum (cold pack) temperatures with an asterisk. Do NOT include a trendline or connect the data points. See other general tips for making graphs in the How to Make a Graph in Excel document located in the Introductory Materials for this lab. Figure 1. The temperature of cold pack described in blue dots showed decrease over time. The hand warmer increased the temperature to an extent until it reached the maximum, and started to decrease as time went on. 8. Putting it all together! Consider the temperature changes experienced by the cold pack and the hand warmer and answer the questions below. a. What was the overall ΔT (change in temperature) for the cold pack? Show your work and include units. ΔT = 14.8 (°C) – 24.2 (°C) = -9.4 (°C) b. What was the overall ΔT (change in temperature) for the hot pack? Show your work and include units. ΔT = 43.1 (°C) – 25.9(°C) = 17.2 (°C) c. Which one worked via an endothermic process? Via an exothermic process? Explain. When temperature of the cold pack decreased, the pack was absorbing heat from the surrounding, so the pack worked via an endothermic process. Hand warmer is an exothermic process since the pack gives off heat. d. Which pack had the greatest change in enthalpy? Explain how you know using your experimental data. Since the change in temperature was greater in hand warmer pack, it would yield greatest change in enthalpy.