Thermodynamics and Gas Laws - Endothermic Vs. Exothermic

Module 5 Lab: Thermodynamics and Gas Laws

3-1: Endothermic vs. Exothermic

In various chemical processes, such as reactions and the dissolving of salts, heat is either absorbed or

given off. This is called enthalpy, meaning "heat energy." We call these events either endothermic (heat in) or exothermic (heat out) processes. The usual procedure to detect these heat events is by measuring the temperature change associated with the process. In this problem, you will dissolve several salts in water, measure the resulting temperature change, and then make deductions about the enthalpy of the process.

1. Start Virtual ChemLab and select Endothermic vs. Exothermic from the list of assignments. The lab will open in the Calorimetry laboratory.

2. There will be a bottle of sodium chloride (NaCl) on the lab bench. A weigh paper will be on the balance with approximately 2 g of NaCl on the paper.

3. The calorimeter will be on the lab bench and filled with 100 ml water. Click the Lab Book to open it.

Make certain the stirrer is On (you should be able to see the shaft rotating). In the thermometer window, click Save to begin recording data. Allow 20-30 seconds to obtain a baseline temperature of the water.

4. Drag the weigh paper with the sample to the calorimeter until it snaps into place and then pour the sample into the calorimeter. Observe the change in temperature until it reaches a maximum and then record data for an additional 20-30 seconds. Click Stop. (You can click on the clock on the wall labeled Accelerate to accelerate the time in the laboratory.) A blue data link will appear in the lab book. Click the data link and record the temperature before adding the NaCl and the highest or lowest temperature after adding the NaCl in the data table.

5. Click the red disposal bucket to clear the lab. Click on the Stockroom to enter. Click on the clipboard and select Preset Experiment #7 and repeat the experiment with NaNO3. Record the initial and final temperatures in the data table.

6. Click the red disposal bucket to clear the lab. Click on the Stockroom to enter. Click the clipboard and select Preset Experiment #8 and repeat the experiment with NaCH3COO (NaAc). Record the initial and final temperatures in the data table.

Data Table

Mixture T1 T2 DT (T2T1)

NaCl (s) + H2O (l) 25 24.8 -0.2

NaNO3 (s) + H2O (l) 25 24.01 -0.99

NaCH3COO + H2O (l) 25 25.97 0.97

Use your experimental data to answer the following questions.

7. Calculate ΔT ( ΔT = T2 - T1) for each mixture and record it in the data table.

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Virtual ChemLab: General Chemistry Laboratories, Student Lab Manual/Workbook, v2.5, Third Edition, by Brian F. Woodfield, Matthew C. Asplund, and Steven Haderlie. Published by Prentice Hall. Copyright © 2006 by Pearson Education, Inc.

8. An exothermic process gives off heat (warms up). An endothermic process absorbs heat (cools off).

Which solutions are endothermic and which are exothermic? What is the sign of the change in enthalpy (DH) in each case? Endothermic NaCl and NaNO3 with a negative value and Exothermic NaAc with a positive value

9. Which solution(s) had little or no change in temperature? NaCl had the smallest change at -0.2

5-1: Boyle's Law: Pressure and Volume

Robert Boyle, a philosopher and theologian, studied the properties of gases in the 17th century. He noticed that gases behave similarly to springs; when compressed or expanded, they tend to "spring" back to their original volume. He published his findings in 1662 in a monograph entitled The Spring of the Air and Its Effects. In this experiment, you will make observations similar to those of Robert Boyle, and learn about the relationship between the pressure and volume of an ideal gas.

1. Start Virtual ChemLab and select Boyle's Law: Pressure and Volume from the list of assignments.

The lab will open in the Gases laboratory.

2. Note that the balloon in the chamber is filled with 0.300 moles of an ideal gas (MW = 4 g/mol) at a temperature of 298 K, a pressure of 1.00 atm, and a volume of 7.336 L. To the left of the Pressure LCD controller is a lever that will decrease and increase the pressure as it is moved up or down; the digit changes depending on how far the lever is moved. Digits may also be clicked directly