Heats of Reaction and Solution

1. Heats of Reaction and Solution 012-10744 r1.04

2. Heats of Reaction and Solution Introduction Each page of this lab that contains the symbol should be inserted into your journal. After completing a lab page with the snapshot symbol, tap (in the upper right hand corner) to insert the page into your journal. Journals and Snapshots The Snapshot button is used to capture the screen. The Journal is where snapshots are stored and viewed. The Share button is used to export or print your journal to turn in your work. Note: You may want to take a snapshot of the first page of this lab as a cover page for your Journal.

3. Heats of Reaction and Solution Lab Challenges • Determine the heat (energy) released or absorbed when sodium hydroxide dissolves in water and when ammonium chloride dissolves in water. • Determine the heat (energy) released or absorbed when magnesium metal reacts with hydrochloric acid. Chemists also provide information on the energy associated with physical and chemical changes. This information is used to evaluate new fuels and efficiently make new products! Chemists make an incredible range of useful products!

4. Heats of Reaction and Solution Background • Physical changes and chemical reactions both may be accompanied by changes in energy, often in the form of heat or enthalpy. • Chemical and physical processes that absorb heat from their surroundings are endothermic. • Chemical and physical processes that release heat into their surroundings are exothermic. Endothermic Heat is absorbed and melts the ice cream. Exothermic Heat is released and warms the surrounding air.

5. Heats of Reaction and Solution Self-Check • What happens during an exothermic reaction? • Heat is taken from the surroundings. • Gas turns into solid. • Heat levels remain the same. • Heat is released into the surroundings.

6. Heats of Reaction and Solution ...Background • Phase changes, including the dissolving of a solute into a solvent, are types of physical changes that involve an exchange of heat. • The heat absorbed or released when a solute dissolves is called the heat of solution (or enthalpy of solution). Heat results from the breaking of attractions between ions in the crystal lattice Break attractions and the forming of attractions between the freed ions and the solvent molecules. Form attractions Solute dissolving in water

7. Heats of Reaction and Solution ...Background • Heat that is released or absorbed during a chemical reaction is called the heat of reaction (or enthalpy of reaction). • The heat of reaction results from the breaking of bonds in the reactants and the forming of bonds in the products. CH4 (g) + 2 O2 (g) → CO2(g) + 2 H2O (l) Reactants- bonds are broken (energy is absorbed) Products- bonds are formed (energy is released)

8. Heats of Reaction and Solution ...Background Enthalpy diagrams illustrate the internal energy of the reactants compared to the products. ENTHALPY DIAGRAM Exothermic Reaction ENTHALPY DIAGRAM Endothermic Reaction Products Reactants Energy Energy Reactants Products Reaction path Reaction path When the final products have more energy than the original reactants, the reaction is endothermic. When the final products have less energy than the starting reactants, the reaction is exothermic.

9. Heats of Reaction and Solution Self-Check • In an endothermic reaction the reactants have _____________________________. • more energy than the products • less energy than the products • the same energy as the products • more or less energy depending on the chemicals reacted

10. Heats of Reaction and Solution Self-Check • In an exothermic reaction, the products have _________ energy (enthalpy), therefore the surroundings must have ______ this energy. • higher, absorbed • higher, emitted • lower, emitted • lower, absorbed • zero, infinite Energy Reaction Path

11. Heats of Reaction and Solution ...Background • The heat of reaction qand heat of solution qcan both be found by multiplying the mass m of the water/solution, the specific heat cof water, and change in temperature ΔTtogether. q = m x cx ΔT • The temperature change of the surroundings is measured and thus the heat calculated is the heat change experienced by the surroundings. The enthalpy of reaction ∆H or heat of solution ∆H, which caused the measured change, is the opposite sign of the heat calculated. ΔH = -q

12. Heats of Reaction and Solution ...Background • Finally, the energy for a physical change or chemical reaction can be described on a per mole basis by dividing the heat of solution or heat of reaction by the number of moles of substance present. • The resulting term is called the molar heat of solution or molar heat of reaction. ΔH Molar heat of solution/reaction = moles of substance

13. Heats of Reaction and Solution Safety • Follow all common laboratory safety procedures. • Sodium hydroxide and hydrochloric acid are corrosive irritants. Avoid contact with the skin and eyes. • Wash hands after handling chemicals, equipment, and glassware. • Be sure that all acids and bases are neutralized before being disposed of down the drain. BE SAFE Always wash hands to remove residue before leaving Neutralize!

14. Heats of Reaction and Solution Materials and Equipment Collect all of these materials before beginning the lab. • Temperature sensor • Beaker, 250-mL • Polystyrene cup, 236-mL (8 oz.) • Centigram balance • Graduated cylinder, 50-mL • Spatula • Weighing paper OR 250-mL

15. Heats of Reaction and Solution Materials and Equipment Collect all of these materials before beginning the lab. • Wash bottle and waste container • Stir rod • Sand paper or steel wool, 1 piece • Sodium hydroxide, 1 g • Ammonium chloride, 1 g • Magnesium metal ribbon, 0.10 g • 1.0 M Hydrochloric acid solution 25 mL • Distilled (deionized) water, 50 mL Na - OH waste Mg Distilled Water

16. Heats of Reaction and Solution Sequencing Challenge The steps to the left are part of the procedure for this lab activity. They are not in the right order. Determine the correct sequence of the steps then take a snapshot of this page. A. Stop recording temperature data after the temperature has stabilized (or reversed). B. Record the exact mass of each reactant. Pour the liquid into the calorimeter and start recording temperature data. D. After the temperature data has stabilized, add the solid to the solution and mix thoroughly. C. Calculate the heat (enthalpy) of reaction or solution.

17. Heats of Reaction and Solution *To Enter Data into a Table: • Tapto open the tool palette. • Tap then tap a cell in the data table to highlight it in yellow. • Tap to open the Keyboard screen. Setup: NaOH • Connect a temperature sensor to the data collection system. • Measure ~1.0 g of sodium hydroxide (NaOH) pellets. Record the exact mass of NaOH in the data table below.*

18. Heats of Reaction and Solution Setup: NaOH Q1: What does it mean to "tare" a balance?

19. Heats of Reaction and Solution *To Enter Data into a Table: • Tapto open the tool palette. • Tap then tap a cell in the data table to highlight it in yellow. • Tap to open the Keyboard screen. Setup: NaOH Measure ~25 mL of water using a graduated cylinder. Enter the exact volume in the table below.* Place a clean, dry calorimeter on the balance and tare the balance. Pour ~25 mL of water into the calorimeter. Enter the mass of the water in the data table below.*

20. Heats of Reaction and Solution Q2:Compare the volume of the water with its mass. Is this what you would expect? Explain.

21. Heats of Reaction and Solution Collect Data: NaOH • Place the calorimeter into a 250-mL beaker and place the temperature sensor in the water. • Tap to start collecting data and allow the temperature to stabilize. Continue to the next page.

22. Heats of Reaction and Solution • 3. Tap then to re-scale the axes and then add the solid NaOH to the water. • Stir the NaOH constantly until it has completely dissolved. This may take several minutes. • Continue collecting data until the temperature has remained constant or started to decrease for at least 30 seconds. • Tap to stop recording data.

23. Heats of Reaction and Solution • Find the initial temperature Ti, the final temperature Tf, and change in temperature ∆T.* • Note:These values will be entered on the next page. • * To Find the Difference Between Two Data Points: • Tap to open the tools. • Tap and then tap two points on the data run. • Adjust using both buttons and then tap . • Tap to display the first point, last point, and the difference between them.

24. Heats of Reaction and Solution • Enter the initial temperature Ti, the final temperature Tf, and change in temperature ∆T for dissolving NaOH in water.* *To Enter Data into a Table: • Tapto open the tool palette. • Tap then tap a cell in the data table to highlight it in yellow. • Tap to open the Keyboard screen.

25. Heats of Reaction and Solution Setup: NH4Cl Q3:Why must the calorimeter, temperature sensor, and stir rod be dried before using them in the next part of the experiment? • Dispose of the NaOH solution according to your teacher's instructions. • Thoroughly clean and dry the calorimeter, temperature sensor, and stir rod. • On the next several pages you will be repeating the experiment, this time dissolving ammonium chloride (NH4Cl) in water.

26. Heats of Reaction and Solution *To Enter Data into a Table: • Tapto open the tool palette. • Tap then tap a cell in the data table to highlight it in yellow. • Tap to open the Keyboard screen. Setup: NH4Cl Measure ~1.0 g of NH4Cl using a blance and ~25 mL of water using a graduated cylinder. Enter the exact values in the table below.* Place a clean, dry calorimeter on the balance and tare the balance. Pour the ~25 mL of water into the calorimeter. Enter the mass of the water below.*

27. Heats of Reaction and Solution Collect Data: NH4Cl • Place the calorimeter into a 250-mL beaker and place the temperature sensor in the water. • Tap to start collecting data and allow the temperature to stabilize. Continue to the next page.

28. Heats of Reaction and Solution • Tap then to re-scale the axes and then add the solid NH4Cl to the water. • Stir the NH4Cl constantly until it has completely dissolved. This may take several minutes. • Continue collecting data until the temperature has remained constant or started to increase for at least 30 seconds. • Tap to stop recording data.

29. Heats of Reaction and Solution • Find the initial temperature Ti, the final temperature Tf, and change in temperature ∆T.* • Note:Tap then tap next to run 1 to hide the first run of data. • * To Find :the Difference Between Two Data Points • Tap to open the tools. • Tap and then tap two points on the data run. • Adjust using both buttons and then tap . • Tap to display the first point, last point, and the difference between them.

30. Heats of Reaction and Solution • Enter the initial temperature Ti, the final temperature Tf, and change in temperature ∆Tfor dissolving NH4Cl in water.* *To Enter Data into a Table: • Tapto open the tool palette. • Tap then tap a cell in the data table to highlight it in yellow. • Tap to open the Keyboard screen.

31. Heats of Reaction and Solution Setup: HCl + Mg Q4:Why is the magnesium ribbon cut into pieces? • Dispose of the NH4Cl solution according to your teacher's instructions. • Thoroughly clean and dry the calorimeter, temperature sensor, and stir rod. • Cut a piece of magnesium (Mg) ribbon that is7-8 cm long (~0.1g). • Use sandpaper/steel wool to remove any magnesium oxide that has formed on the Mg ribbon. • Cut the cleaned ribbon into ~1 cm pieces.

32. Heats of Reaction and Solution *To Enter Data into a Table: • Tapto open the tool palette. • Tap then tap a cell in the data table to highlight it in yellow. • Tap to open the Keyboard screen. Setup: HCl + Mg Determine the mass of all the pieces together and record it in the data table below.* Measure ~25 mL of 1.0 M hydrochloric acid (HCl), record its volume, and determine its mass by taring a clean, dry calorimeter and then adding the HCl. Enter the values in the data table below.*

33. Heats of Reaction and Solution Collect Data: HCl + Mg • Place the calorimeter into a 250-mL beaker and place the temperature sensor in the water. • Tap to start collecting data and allow the temperature to stabilize. Continue to the next page.

34. Heats of Reaction and Solution • Tap then to re-scale the axes and then add the Mg pieces to the HCl. • Stir until the magnesium has completely reacted. This may take several minutes. • Continue collecting data until the temperature has remained constant or started to decrease for at least 30 seconds. • Tap to stop recording data.

35. Heats of Reaction and Solution Collect Data: HCl+ Mg Q5:What evidence did you observe that a chemical reaction occurred between HCl and Mg?

36. Heats of Reaction and Solution • Find the initial temperature Ti, the final temperature Tf, and change in temperature ∆T.* • Note:Tap then tap next to run 1 and run 2 to hide these data runs. • * To Find :the Difference Between Two Data Points • Tap to open the tools. • Tap and then tap two points on the data run. • Adjust using both buttons and then tap . • Tap to display the first point, last point, and the difference between them.

37. Heats of Reaction and Solution • Enter the initial temperature Ti, the final temperature Tf, and change in temperature ∆Tfor reacting HCl with Mg.* *To Enter Data into a Table: • Tapto open the tool palette. • Tap then tap a cell in the data table to highlight it in yellow. • Tap to open the Keyboard screen.

38. Heats of Reaction and Solution Data Analysis 1. Calculate the heatabsorbed by the solution in each process. Enter your answers in the data table. Convert joules to kilojoules in the final column. q = m × c× ΔT q = heat lost or gained by the solution • m = mass of the liquid • c = the specific heat of the solution (4.18 J/g°C) • ΔT= change in temperature

39. Heats of Reaction and Solution Data Analysis • Determine the number of moles of each solid used. • mass • moles = • molar mass • Determine ∆H for each process. • ΔH=-q • Determine the molar enthalpy (∆H/mol) for each substance. • Enter all values in the data table on the left.

40. Heats of Reaction and Solution Analysis • Determine the percent error for each process using the accepted values in the table below. Enter the percent error in the table below. (accepted value - experimental value) percent error = × 100 accepted value

41. Heats of Reaction and Solution Analysis • Suggest possible improvements to the experimental procedure that could improve the accuracy of the results.

42. Heats of Reaction and Solution Analysis • Identify each process as exothermic or endothermic: • dissolving NaOH • dissolving NH4Cl • reacting Mg + HCl

43. Heats of Reaction and Solution Analysis • Write the chemical equation that illustrates the heat changes that occurred for each physical and chemical process you performed in this experiment. Use your experimentally determined values for molar heat of reaction/solution in the equations. Be sure to include state symbols for all reactants and products.

44. Heats of Reaction and Solution Synthesis • Describe what happens at the molecular level to sodium hydroxide when it is dissolved in water. Solute dissolving in water

45. Heats of Reaction and Solution Synthesis • Heat was either released or absorbed in all three processes, but only one of the processes was a chemical reaction. Explain how this is possible.

46. Heats of Reaction and Solution Synthesis • Describe what would have happened if the physical and chemical processes were performed at 50°C instead of room temperature?

47. Heats of Reaction and Solution Multiple Choice • Heat of reaction refers to ______________. • the heat released by a chemical reaction. • the heat absorbed by a chemical reaction. • the temperature of the solution after a chemical reaction occurs. • both A and B.

48. Heats of Reaction and Solution Multiple Choice • Using the chemical equation below, determine the energy released by burning 2 moles of propane (C3H8). • 2219.2 kJ • 4438.4 kJ • 1109.6 kJ • 11096 kJ C3H8(g) + 5O2(g) →3CO2(g) + 4H2O(l) + 2219.2 kJ

49. Heats of Reaction and Solution Multiple Choice Read the information below to answer the next three questions. Two grams of salt A were added to 50 mL of water and the initial and final temperatures were recorded below. In a separate experiment, two grams of salt B were added to 50 mL of water and the initial and final temperatures were recorded below. SALT A SALT B Initial Temp = 20°C Initial Temp = 20°C Final Temp = 35°C Final Temp = 10°C

50. Heats of Reaction and Solution Multiple Choice SALT A Initial Temp = 20°C • Using the information on the previous page, what can be said about flow of energy in the Salt A and Salt B experiments? • For salt A: energy flows from the water to the salt; For salt B: energy flows from the water to the salt. • For salt A: energy flows from the salt to the water; For salt B: energy flows from the salt to the water. • For salt A: energy flows from the salt to the water; For salt B: energy flows from the water to the salt. • For salt A: energy flows from the water to the salt; For salt B: energy flows from the salt to the water. Final Temp = 35°C SALT B Initial Temp = 20°C Final Temp = 10°C