Heats of Reaction and Solution
012-10744 r1.04
Heats of Reaction and Solution
Introduction
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.
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.
Note: You may want to take a
snapshot of the first page of
this lab as a cover page for
your Journal.
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 make an
incredible range of useful
products!
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!
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.
Endothermic
Heat is absorbed
and melts the ice
cream.
• Chemical and physical processes that
absorb heat from their surroundings
are endothermic.
• Chemical and physical processes that
release heat into their surroundings
are exothermic.
Exothermic
Heat is released and
warms the surrounding
air.
Heats of Reaction and Solution
Self-Check
1. What happens during an exothermic reaction?
a) Heat is taken from the surroundings.
b) Gas turns into solid.
c) Heat levels remain the same.
d) Heat is released into the surroundings.
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.
Solute dissolving in water
Form attractions
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)
Reactants- bonds are broken
(energy is absorbed)
→
CO2 (g)
+
2 H2O (l)
Products- bonds are formed
(energy is released)
Heats of Reaction and Solution
...Background
Enthalpy diagrams illustrate the internal energy of the reactants compared to the
products.
ENTHALPY DIAGRAM
Exothermic Reaction
Products
Reactants
Reaction path
When the final products have more energy
than the original reactants, the reaction is
endothermic.
Energy
Energy
ENTHALPY DIAGRAM
Endothermic Reaction
Reactants
Products
Reaction path
When the final products have less energy
than the starting reactants, the reaction is
exothermic.
Heats of Reaction and Solution
Self-Check
2. In an endothermic reaction the reactants have
_____________________________.
a) more energy than the products
b) less energy than the products
c) the same energy as the products
d) more or less energy depending on the
chemicals reacted
Heats of Reaction and Solution
3. In an exothermic reaction, the products have
_________ energy (enthalpy), therefore the
surroundings must have ______ this energy.
a) higher, absorbed
b) higher, emitted
c) lower, emitted
d) lower, absorbed
e) zero, infinite
Energy
Self-Check
Reaction Path
Heats of Reaction and Solution
...Background
• The heat of reaction q and heat of solution q can both be found by multiplying
the mass m of the water/solution, the specific heat c of water, and change in
temperature ΔT together.
q = m x c x 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
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
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
Neutralize!
Always wash hands
to remove residue
before leaving
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
Heats of Reaction and Solution
Materials and Equipment
Collect all of these materials before beginning the lab.
waste
• Wash bottle and waste container
• Stir rod
• Sand paper or steel wool, 1 piece
Na - OH
• 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
Mg
Distilled
Water
Heats of Reaction and Solution
Sequencing Challenge
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.
C. Calculate the heat
(enthalpy) of
reaction or solution.
D. After the
temperature data
has stabilized, add
the solid to the
solution and mix
thoroughly.
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.
Heats of Reaction and Solution
Setup: NaOH
1. Connect a temperature sensor to the data
collection system.
2. Measure ~1.0 g of sodium hydroxide (NaOH)
pellets. Record the exact mass of NaOH in the data
table below.*
*To Enter Data into a Table:
1. Tap
to open the tool
palette.
2. Tap
then tap a cell in
the data table to highlight it
in yellow.
3. Tap
to open the
Keyboard screen.
Heats of Reaction and Solution
Setup: NaOH
Q1: What does it mean to "tare" a balance?
Heats of Reaction and Solution
Setup: NaOH
3. Measure ~25 mL of water using a graduated cylinder.
Enter the exact volume in the table below.*
4. 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.*
*To Enter Data into a Table:
1. Tap
to open the tool
palette.
2. Tap
then tap a cell in
the data table to highlight it
in yellow.
3. Tap
to open the
Keyboard screen.
Heats of Reaction and Solution
Q2: Compare the volume of
the water with its mass. Is
this what you would
expect? Explain.
Heats of Reaction and Solution
Collect Data: NaOH
1. Place the calorimeter into
a 250-mL beaker and place
the temperature sensor in
the water.
2. Tap
to start collecting
data and allow the
temperature to stabilize.
Continue to the next page.
Heats of Reaction and Solution
3. Tap
then
to re-scale
the axes and then add the
solid NaOH to the water.
4. Stir the NaOH constantly
until it has completely
dissolved. This may take
several minutes.
5. Continue collecting data
until the temperature has
remained constant or
started to decrease for at
least 30 seconds.
6. Tap
data.
to stop recording
Heats of Reaction and Solution
7. 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:
1. Tap
to open the tools.
2. Tap
and then tap two
points on the data run.
3. Adjust using both
buttons
and then tap
.
4. Tap
to display the first
point, last point, and the
difference between them.
Heats of Reaction and Solution
8. 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:
1. Tap
to open the tool
palette.
2. Tap
then tap a cell in
the data table to highlight it
in yellow.
3. Tap
to open the
Keyboard screen.
Heats of Reaction and Solution
Setup: NH4Cl
1.
Dispose of the NaOH solution according to your
teacher's instructions.
2.
Thoroughly clean and dry the calorimeter,
temperature sensor, and stir rod.
3.
On the next several pages you
will be repeating the experiment,
this time dissolving ammonium
chloride (NH4Cl) in water.
Q3: Why must the
calorimeter, temperature
sensor, and stir rod be
dried before using them
in the next part of the
experiment?
Heats of Reaction and Solution
Setup: NH4Cl
4. 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.*
5. 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.*
*To Enter Data into a Table:
1. Tap
to open the tool
palette.
2. Tap
then tap a cell in
the data table to highlight it
in yellow.
3. Tap
to open the
Keyboard screen.
Heats of Reaction and Solution
Collect Data: NH4Cl
1. Place the calorimeter into
a 250-mL beaker and place
the temperature sensor in
the water.
2. Tap
to start collecting
data and allow the
temperature to stabilize.
Continue to the next page.
Heats of Reaction and Solution
3. Tap
then
to rescale the axes and then
add the solid NH4Cl to the
water.
4. Stir the NH4Cl constantly
until it has completely
dissolved. This may take
several minutes.
5. Continue collecting data
until the temperature has
remained constant or
started to increase for at
least 30 seconds.
6. Tap
data.
to stop recording
Heats of Reaction and Solution
7. 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
1. Tap
to open the tools.
2. Tap
and then tap two
points on the data run.
3. Adjust using both
buttons
and then tap
.
4. Tap
to display the first
point, last point, and the
difference between them.
Heats of Reaction and Solution
8. Enter the initial
temperature Ti, the final
temperature Tf, and
change in temperature ∆T
for dissolving NH4Cl in
water.*
*To Enter Data into a Table:
1. Tap
to open the tool
palette.
2. Tap
then tap a cell in
the data table to highlight it
in yellow.
3. Tap
to open the
Keyboard screen.
Heats of Reaction and Solution
Setup: HCl + Mg
1. Dispose of the NH4Cl solution according to your
teacher's instructions.
2. Thoroughly clean and dry the calorimeter,
temperature sensor, and stir rod.
3. Cut a piece of magnesium (Mg) ribbon that is
7-8 cm long (~0.1g).
4. Use sandpaper/steel wool to remove any
magnesium oxide that has formed on the Mg ribbon.
5. Cut the cleaned ribbon into ~1 cm pieces.
Q4: Why is the magnesium
ribbon cut into pieces?
Heats of Reaction and Solution
Setup: HCl + Mg
6. Determine the mass of all the pieces together and record
it in the data table below.*
7. 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.*
*To Enter Data into a Table:
1. Tap
to open the tool
palette.
2. Tap
then tap a cell in
the data table to highlight it
in yellow.
3. Tap
to open the
Keyboard screen.
Heats of Reaction and Solution
Collect Data: HCl + Mg
1. Place the calorimeter into
a 250-mL beaker and place
the temperature sensor in
the water.
2. Tap
to start collecting
data and allow the
temperature to stabilize.
Continue to the next page.
Heats of Reaction and Solution
3. Tap
then
to re-scale
the axes and then add the
Mg pieces to the HCl.
4. Stir until the magnesium
has completely reacted.
This may take several
minutes.
5. Continue collecting data
until the temperature has
remained constant or
started to decrease for at
least 30 seconds.
6. Tap
to stop recording
data.
Heats of Reaction and Solution
Collect Data: HCl + Mg
Q5: What evidence did you observe that a chemical reaction occurred
between HCl and Mg?
Heats of Reaction and Solution
7. 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
1. Tap
to open the tools.
2. Tap
and then tap two
points on the data run.
3. Adjust using both
buttons
and then tap
.
4. Tap
to display the first
point, last point, and the
difference between them.
Heats of Reaction and Solution
8. Enter the initial
temperature Ti, the final
temperature Tf, and
change in temperature ∆T
for reacting HCl with Mg.*
*To Enter Data into a Table:
1. Tap
to open the tool
palette.
2. Tap
then tap a cell in
the data table to highlight it
in yellow.
3. Tap
to open the
Keyboard screen.
Heats of Reaction and Solution
Data Analysis
1. Calculate the heat absorbed
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
Heats of Reaction and Solution
Data Analysis
2. Determine the number of
moles of each solid used.
mass
moles =
molar mass
3. Determine ∆H for each
process.
ΔH = -q
4. Determine the molar
enthalpy (∆H/mol) for
each substance.
Enter all values in the data table
on the left.
Heats of Reaction and Solution
Analysis
1. Determine the percent error for each process using the accepted values in the
table below. Enter the percent error in the table below.
percent error =
(accepted value - experimental value)
accepted value
× 100
Heats of Reaction and Solution
Analysis
2. Suggest possible improvements to the experimental procedure that could
improve the accuracy of the results.
Heats of Reaction and Solution
Analysis
3. Identify each process as exothermic or endothermic:
a. dissolving NaOH
b. dissolving NH4Cl
c. reacting Mg + HCl
Heats of Reaction and Solution
Analysis
4. 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.
Heats of Reaction and Solution
Synthesis
1. Describe what happens at the
molecular level to sodium hydroxide
when it is dissolved in water.
Solute dissolving in water
Heats of Reaction and Solution
Synthesis
2. 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.
Heats of Reaction and Solution
Synthesis
3. Describe what would have happened if the physical and chemical processes were
performed at 50°C instead of room temperature?
Heats of Reaction and Solution
Multiple Choice
1. Heat of reaction refers to ______________.
a) the heat released by a chemical reaction.
b) the heat absorbed by a chemical reaction.
c) the temperature of the solution after a
chemical reaction occurs.
d) both A and B.
Heats of Reaction and Solution
Multiple Choice
2. Using the chemical equation below, determine the
energy released by burning 2 moles of propane
(C3H8).
C3H8(g) + 5O2(g) → 3CO2(g) + 4H2O(l) + 2219.2 kJ
a) 2219.2 kJ
b) 4438.4 kJ
c) 1109.6 kJ
d) 11096 kJ
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
Heats of Reaction and Solution
Multiple Choice
3. Using the information on the previous page,
what can be said about flow of energy in the
Salt A and Salt B experiments?
a) For salt A: energy flows from the water to the salt;
For salt B: energy flows from the water to the salt.
b) For salt A: energy flows from the salt to the water;
For salt B: energy flows from the salt to the water.
c) For salt A: energy flows from the salt to the water;
For salt B: energy flows from the water to the salt.
d) For salt A: energy flows from the water to the salt;
For salt B: energy flows from the salt to the water.
SALT A
Initial Temp = 20°C
Final Temp = 35°C
SALT B
Initial Temp = 20°C
Final Temp = 10°C
Heats of Reaction and Solution
Multiple Choice
4. What type of process occurred when salt A
dissolved in water?
a) enthalpy
b) heat
c) endothermic
d) exothermic
SALT A
Initial Temp = 20°C
Final Temp = 35°C
SALT B
Initial Temp = 20°C
Final Temp = 10°C
Heats of Reaction and Solution
Multiple Choice
5. Which equation illustrates the process that
occurred when salt B dissolved in water?
a) salt B(s) → salt B(aq) + heat
b) salt B(aq) → salt B(aq) + heat
c) salt B(s) + heat → salt B(aq)
d) salt B(aq) + heat → salt B(aq)
SALT A
Initial Temp = 20°C
Final Temp = 35°C
SALT B
Initial Temp = 20°C
Final Temp = 10°C
Heats of Reaction and Solution
Congratulations!
You have completed the lab.
Please remember to follow your teacher's instructions for cleaning-up and submitting
your lab.
Heats of Reaction and Solution
References
All images were taken from PASCO documentation, public domain clip art, or Wikimedia Foundation Commons.
1.HOT SPRING. Public domain compliments of creator, Matt Fishbach
2.ATOMIC SYMBOL. http://www.openstockphotography.org/image-licensing/energy/Nuclear_energy_icon.jpg
3.ACTIVATION ENERGY DIAGRAM. http://en.wikipedia.org/wiki/Image:Activation_energy.svg
4.GAS PUMP http://freeclipartnow.com/transportation/traffic-signs/us-road-signs/recreation/gas.jpg.html
5.SQUEAKY CLEAN http://freeclipartnow.com/household/chores/cleaners/disfectant.jpg.html
6.PAINT http://freeclipartnow.com/recreation/art/paint-can-n-brush.jpg.html
7.BATTERY http://freeclipartnow.com/science/energy/batteries/battery.jpg.html
8.ELECTRIC SOCKET http://freeclipartnow.com/electronics-technology/computers/icons-themes/flattheme/applications/energy.png.html
9.BURNING MATCH http://freeclipartnow.com/construction/tools/lit-match.jpg.html
10.ICE CREAM http://freeclipartnow.com/food/desserts-snacks/ice-cream/ice-cream-cone-3-scoop.jpg.html
11.CORROSIVE WARNING http://commons.wikimedia.org/wiki/Image:DIN_4844-2_Warnung_vor_Aetzenden_Stoffen_DW004.svg
12.BE SAFE http://freeclipartnow.com/signs-symbols/warnings/safety-hands.jpg.html
13.BEAKER http://freeclipartnow.com/science/flasks-tubes/beaker.jpg.html
14.VINEGAR (DISTILLED WATER) http://freeclipartnow.com/household/chores/cleaners/vinegar.jpg.html
15.NAOH http://commons.wikimedia.org/wiki/File:NaOH.gif
16.STOVE http://commons.wikimedia.org/wiki/File:MSR_WindPro_portable_stove.jpg