1
Hess's Law Virtual Lab
Hyperlink: http://chemcollective.org/vlab/138
In this experiment you will determine and compare the quantity of heat energy released in three
exothermic chemical reactions.
Reaction 1: Solid sodium hydroxide dissolves in water to form an aqueous solution of ions
Reaction 2: Solid sodium hydroxide reacts with an aqueous solution of hydrogen chloride to form water
and an aqueous solution of sodium chloride
Reaction 3: An aqueous solution of sodium hydroxide reacts with an aqueous solution of hydrogen
chloride to form water and an aqueous solution of sodium chloride.
For this experiment, a Styrofoam cup will act as the calorimeter. We can assume that any heat
transferred to the Styrofoam and surrounding air will be negligible. We can also assume that the specific
heat of water is 4.18J/g°C
Procedure
Reaction 1
1. In the glassware menu, take out 50mL graduated cylinder and a foam cup. From the instruments
menu, take out the scale. From the chemical stockroom, move the distilled water and solid
NaOH onto the workbench.
2. Transfer 50.0mL of water to the foam cup. (Drag water onto graduated cylinder; it will turn blue
and a text-bar will active at the bottom of the screen, enter "50.0" and click on pour)
3. Mass 1.00 g of solid NaOH directly into the foam cup and record its mass to the nearest 0.01g
(Place cup on balance, once it registers a mass, click the "Tare" button, Drag NaOH bottle onto
foam cup, when you release mouse, it will be tipped to show it is in pour mode)
4. Click on graduated cylinder to record its temperature
5. Drag graduated cylinder onto foam cup (it will be tipped, enter "50.0" in the transfer bar and
click pour)
6. Record highest temperature
Reaction 2
1. Take 0.5 M HCl from strong acids cabinet, as well as a foam cup and 50mL graduated cylinder
from glassware menu.
2. Transfer 50.0mL of 0.5 M HCl to the foam cup.
3. Mass 1.00 g of solid NaOH directly into the foam cup and record its mass to the nearest 0.01g
Click on graduated cylinder to record its temperature.
4. Drag graduated cylinder onto foam cup (it will be tipped, enter "50.0" in the transfer bar and
click pour)
5. Record highest temperature
Reaction 3
1. Take out new graduated cylinder and fresh foam cup (remove old ones). Take out 1.0M HCl and
1.0 M NaOH
2. Measure 25.0mL of 1.0 M HCl and pour into foam cup
3. Pour an equal volume of 1.0 M NaOH into graduated cylinder
4. Record temperature of 1.0 M HCl and 1.0 M NaOH
5. Pour 1.0 M NaOH solution into foam cup
6. Record highest temperature
A. Di Lallo
2
Data Analysis
1. Write the chemical equations for reactions 1 through 3
2. Complete the table using collected data and calculations
Reaction
Mass NaOH
(g)
Initial
Temp (°C)
Final Temp
(°C)
QNaOH (kJ)
Moles of
Molar Heat of
NaOH (mol) rxn (kJ/mol)
Sample calculations
3. Re-write the chemical equations for reactions 1 through 3, including the ΔH for each reaction.
4. Supposed you had used 4.00g of NaOH(s) in reaction 1. Assuming no change in ΔT, calculate Qwater,
QNaOH and ΔHsolution. What can you say about the calculated ΔHsolution and the ΔHsolution from reaction 1?
A. Di Lallo