Virtual Lab – Endothermic and Exothermic Reactions
Many chemical reactions give off energy. Chemical reactions that release energy are called exothermic reactions. Some chemical reactions absorb energy and are called endothermic reactions. In this lab, you will study various reactions using a calorimeter to determine if they are exothermic or endothermic and determine the heat of reaction (ΔHrxn) for each.
OBJECTIVES
In this experiment, you will
· Become familiar with using a virtual calorimeter to determine whether a reaction is exothermic or endothermic
· Interpret calorimeter data using a temperature versus time graph.
· Calculate the heat of reaction for various chemical reactions
PROCEDURE
Go to: https://media.pearsoncmg.com/bc/bc_0media_chem/chem_sim/calorimetry/Calor.php
Click on “Experiment” tab.
Click on “Run Experiment” button (If you wish, you may click on the “Watch Demo” tab)
Part I Potassium Chloride in Water
1. Beneath the beaker on the balance, choose the solid tab.
2. Using the pull-down menu for solids, choose potassium chloride (KCl).
3. Set the mass to be 10.0 g using the slider.
4. Keep the temperature at 20.0 Celsius
5. Click on the “Show ΔH” button.
6. Click NEXT which will take you to the settings beneath the calorimeter.
7. Beneath the calorimeter, choose the liquids tab.
8. Choose water as your liquid.
9. Set the mass to be 150.0 g using the slider.
10. Keep the temperature at 20.0 Celsius
11. Click on the “Show ΔH” button.
12. Click NEXT which will allow you to start the calorimetric experiment.
13. Under the “Run Experiment” tab, click both “Show Graph View” AND “Show Microscopic View”
14. Click START to begin your calorimetric experiment!
15. The initial temperature was 20.0 degrees; RECORD your final temperature
Part II NaOH and HCl Neutralization Reaction
1. Click on the reset button to begin a new experiment. Beneath the beaker on the balance, choose the “Solutions” tab.
2. Using the pull-down menu for solutions, choose sodium hydroxide (NaOH)
3. Set the volume to be 50.0 mL using the slider.
4. Set the molarity to be 1.0 M using the slider.
5. Click on the “Show ΔH” button.
6. Click NEXT which will take you to the settings beneath the calorimeter.
7. Beneath the calorimeter, choose the “solutions” tab.
8. Using the pull-down menu for solutions, choose hydrochloric acid (HCl)
9. Set the volume to be 50.0 mL using the slider.
10. Set the molarity to be 1.0 M using the slider.
11. Click on the “Show ΔH” button.
12. Click NEXT which will allow you to start the calorimetric experiment.
13. Under the “Run Experiment” tab, click both “Show Graph View” AND “Show Microscopic View”
14. Click START to begin your calorimetric experiment!
15. The initial temperature was 20.0 degrees; RECORD your final temperature
Part III: Your Turn to Experiment with Your Virtual Calorimeter!
1. Beneath the beaker on the balance, choose the solid tab.
2. Using the pull-down menu for solids, choose a solid of your choice (but not potassium chloride!).
3. Set the mass to be whatever you wish using the slider.
4. Keep the temperature at 20.0 Celsius
5. Click on the “Show ΔH” button.
6. Click NEXT which will take you to the settings beneath the calorimeter.
7. Beneath the calorimeter, choose the liquids tab.
8. Choose water as your liquid.
9. Set the mass to be whatever you wish using the slider.
10. Keep the temperature at 20.0 Celsius
11. Click on the “Show ΔH” button.
12. Click NEXT which will allow you to start the calorimetric experiment.
13. Under the “Run Experiment” tab, click both “Show Graph View” AND “Show Microscopic View”
14. Click START to begin your calorimetric experiment!
15. The initial temperature was 20.0 degrees; RECORD your final temperature.
16. Take a SCREEN SHOT of your completed experiment (and include it on Question 6 of the Post Lab Requirements)
POST LAB REQUIREMENTS (to be submitted electronically to your instructor)
1. Calculate the temperature change, t, for each of the three reactions by subtracting the initial temperature, t1, from the final temperature, t2 (t = t2 – t1). Show you data in table.
2. For each reaction, is the reaction endothermic or exothermic? Explain.
3. For Part I, find ΔHrxn (in units of kJ/mol of KCl) using q = mCsΔT. Recall, that you measured the change in the temperature of the entire system in the calorimeter, so be careful what value you use for “m” (big hint: use the mass of KCl + H20!). Use Cs for water (4.184 J/g C). The above equation allows you to find q. But in order to find ΔHrxn (in units of kJ/mol of KCl) you must divide q by the total number of moles of KCl you used (you know the mass in g from the experiment). You must also divide by 1000 to report as KJ/mol rather than J.
4. For Part II, find ΔHrxn (in units of kJ/mol of NaOH) using q = mCsΔT. Recall, that you measured the change in the temperature of the entire system in the calorimeter, so be careful what value you use for “m” (big hint: assume the combined solution has a density of 1 g/mL and use the combined volumes of the two solutions to calculate the mass of the combined solution). Use Cs for water (4.184 J/g C). The above equation allows you to find q. But in order to find ΔHrxn (in units of kJ/mol of NaOH) you must divide q by the total number of moles of NaOH you used (you know the volume of NaOH, and the molarity, from the experiment). You must also divide by 1000 to report as KJ/mol rather than J.
5. Do the signs on the calculated ΔHrxn (Part I and II) agree with your assessment of which reaction was endothermic and which was exothermic? Explain.
6. For Part III, what solid did you choose? Include a screen shot of the completed experiment. You do not need to calculate the ΔHrxn, unless you really want to!
