Measuring and Comparing the Amount of Heat Energy Released or Absorbed within Chemical
Reactions
Carly Cox
11/08/2020
Chem 113 (1)
Introduction
In this experiment, three chemical reactions are being observed and analyzed in order to
determine the change in temperature that occurs during the reaction. The purpose of this
experiment is to measure the temperature change within each reaction and then apply Hess’s law
to conclude if the enthalpy difference that occurs in Reaction 1 and Reaction 2 are equal to the
change in enthalpy in Reaction 3. Hess’s law is highly utilized when calculating the amount of
heat when there are multiple reactions. It can be applied in real life situations as well. For
example, previous literature uses an example of how much energy a car burns as fuel in different
circumstances is a real-life example of when Hess’s law can be utilized in everyday life (Averill
& Eldredge, 2007).
This experiment examines three reactions. The first reaction is made up of sodium hydroxide
(solid) that will dissolve within water. This will result in an aqueous solution to be the product of
this reaction. The second reaction is where solid sodium hydroxide will mix with an aqueous
solution made up with hydrochloric acid to form a product of water and sodium chloride in an
aqueous state. The third reaction used within this experiment, is sodium hydroxide in an aqueous
state combining with hydrogen chloride in an aqueous state which forms a product of water and
sodium chloride in aqueous state. In this experiment, calorimetry is utilized to determine the heat
amount transferred within each reaction. To determine this measurement the equation below
must be used:
∆𝑯 = 𝒒𝒑
The symbol ΔH stands for change in enthalpy and the symbol qp stands for heat at constant
pressure. This equation will be used to measure the heat transfer that occurs that occurs within
Reaction 1, Reaction 2, and Reaction 3. This experiment also requires the equation:
𝒒𝒔𝒐𝒍𝒖𝒕𝒊𝒐𝒏 = 𝒎𝑪∆𝑻
This equation measures the temperature change that occurs in an aqueous reaction. This equation
utilizes the symbol q which symbolizes the change in energy occurring within a reaction. It also
utilizes m which stands for mass, C which symbolizes the specific heat capacity, and ∆𝑻 which
stands for the temperature change that occurs within a reaction. This can be configured by
subtracting the ending temperature to the temperature found at the beginning. This experiment
also requires the use of the equation to calculate the heat exchange that occurs within the
reaction. The equation that is used to in this experiment to determine the heat exchange within
each reaction is:
𝒒𝒓𝒙𝒏 = −(𝒒𝒔𝒐𝒍𝒖𝒕𝒊𝒐𝒏 + 𝒒𝒄𝒂𝒍𝒐𝒓𝒊𝒎𝒆𝒕𝒆𝒓 )
This equation is solved by adding the heat within the reaction and the heat of the calorimeter. By
adding the two together the heat exchange that occurs within each reaction can be determined.
Hess’s law will be utilized during this experiment to allow the experimenter to deduce if the
enthalpy change for Reaction 1 and Reaction 2 is the same as the enthalpy change that occurs
within Reaction 3. It is hypothesized that given the information that Reaction 1 and Reaction 2
both include chemicals that are included within Reaction 3, that the enthalpy change from
Reaction 1 and Reaction 2 will be equivalent to the enthalpy change that is seen in Reaction 3.
Experimental Procedure
This experiment utilizes the virtual laboratory which allows the experimenter to conduct realistic
experiments in an online setting. Once the experimenter enters the virtual laboratory, they will
complete the first component of the experiment which is to determine the heat within each
reaction that is being examined. For this to be completed for Reaction 1, the experimenter must
add 50.0 mL to a foam cup and record the pH and temperature. Next, the experimenter must
combine that 50.0 mL of distilled water and precisely 1.00 grams of NaOH in an insulated foam
cup. Once this step is completed, the pH level and temperature must be collected. Reaction 2 will
also be assessed by transferring 50.0 mL of 0.5 M hydrochloric acid into a foam cup and
recording the pH and temperature. Next, the experimenter will combine 50.0 mL of 0.5 M
hydrochloric acid and 1.00 grams of NaOH in a foam cup and then measure what the highest
temperature and the pH level within this reaction. Reaction 3 will also be assessed using similar
methods. 25.0 mL of 1.0 M HCl and 25 mL of 1.0 M NaOH are combined within a foam cup and
then the highest temperature and pH level of the reaction is collected.
The next component of this experiment relies on the data collected in the prior step. In each
reaction record the change in temperature that occurs, the heat absorbed by the solution, the
amount of moles of sodium hydroxide that are in the solution, and amount of heat evolved within
the solution. These calculations recorded side by side allow the experimenters to make
comparisons between the three reactions. By determining the sum of energies within Reaction 1
and Reaction 2 and for Reaction 3, the experimenter can determine if the enthalpy change in
Reaction 1 and Reaction 2 are equal to Reaction 3.
Data and Calculations
Reaction 1
Change in
temperature
Tfinal - Tinitial (°C)
Heat absorbed
by the solution
𝒒𝒔𝒐𝒍𝒖𝒕𝒊𝒐𝒏
= 𝒎𝑪∆𝑻
Number of moles
of sodium
hydroxide
present
Amount of
heat evolved
𝒒𝒓𝒙𝒏
= −(𝒒𝒔𝒐𝒍𝒖𝒕𝒊𝒐𝒏
+ 𝒒𝒄𝒂𝒍𝒐𝒓𝒊𝒎𝒆𝒕𝒆𝒓 )
30.3°C-25°C=
5.3°C
m = 50g
c = 4.184 J /g°C
Δt = 30.3°C –
25°C
m- 1g
mm of NaOH39.997g/mol
Q (reaction )
= -m* C water
*∆T = - 50g
*4.184 J/g∙°C *
5.5 °C =
-1150.6
J/1000=
-1.1506
kJ/mol
50g
*4.184J/g°C*
5.3°C =
1108.76J/1000=
1.108 kJ
1g/39.997g/mol=
0.025 mol
Reaction 2
Reaction 3
36.97°C-25°C=
11.97°C
31.67°C-25°C=
6.67°C
m = 50g
c = 4.184 J /g°C
Δt = 36.97°C 25°C
m- 1g
mm of NaOH39.997g/mol
1g/39.997g/mol=
0.025 mol
50g*4.184
J/g°C*11.97°C =
2504.124
J/1000= 2.504
kJ
m = 50g
c = 4.184 J /g°C
Δt = 31.67°C 25°C
V= 25 mL
Molarity NaOH1.0
25 mL/1000=
0.025 L
50g*4.184
J/g°C*6.67°C =
J/1000=
1395.364
J/1000= 1.395
kJ
Initial pH
Reaction 1
Mass of
NaOH
1g
Reaction 2
Reaction 3
1.0 M*0.025 L=
0.025 mol
Final pH
7
Initial
Temp
25°C
13.52
Final
Temp
30.3°C
1g
0.30
25°C
9.18
36.97°C
25 g
1M HCL0.00
1M NaOH14.00
25°C
6.89
31.67°C
Net Ionic Equations
Reaction 1: NaOH (s) + H2O (l)
Na+ (aq) + OH- (aq)
Reaction 2: NaOH (s) + H+ (aq)
Na+ (aq) + H2O (l)
Reaction 3: OH- (aq) + H+ (aq)
H2O (l)
Q (reaction )
= -m* C water
*∆T = - 50g
*4.184 J/g°C *
12 °C =
-2510.4 J/1000
=
-2.5104 kJ/
mol
Q (reaction)
= -m* C water
*∆T = - 50 g
*4.184 J/g°C *
6.7°C =
-1401.64
J/1000=
-1.4016
kJ/mol
Compare the Sum of the Heats of Reaction for 1 and 2 to Heat of Reaction for Reaction 3
ΔH1 = +44.35
ΔH2 = -100.42
ΔH3 = -56.07
ΔH1 + ΔH2
= +44.35 + -100.42= -56.07
ΔH1 + ΔH2 = ΔH3
The sum of the heats of reaction for 1 and 2 is equal to heat of reaction for reaction 3.
Discussion
This experiment allows the experimenter to have the opportunity to compare and examine three
chemical reactions. By measuring temperature change and other thermochemistry variables, the
experimenter is able to determine a multitude of information about the reaction. In this
experiment the information collected allows the experimenter to measure the sum of the heats of
the reactions to determine if the sum of the heats of reaction for 1 and 2 are equivalent to the heat
of reaction for reaction 3. The sum of heat for reaction 1 and reaction 2 equates to be -56.07.
This can be determined by finding the enthalpy of the reaction. This can be determined by
finding the heat absorbed by the solution and dividing this by the moles of NaOH that are present
within that reaction. When the heat absorbed is divided by the moles of NaOH for reaction 1, it is
determined that the enthalpy is 44.35. For reaction 2, the enthalpy is determined to be -100.42.
When those figures are added together the heat of reaction for reaction 3 can be configured (ΔH1
+ ΔH2 = ΔH3) which would equate to be -56.07. This experiment illustrates the concept of
Hess’s law. The information collected during this experiment determines that the hypothesis
made prior to the execution of the experiment is correct. Hess’s law and the law of conservation
of energy assert the same concept regarding energy within reactions. The main concept of the
law of conservation of energy asserts that there is no loss or gain regarding energy. Energy only
has the ability to be altered from a state perspective (Bekhterev & Strickland, 2017). Energy is
not added or lost at any point, however it can be altered. This concept also applies to Hess’s law
which asserts that a reaction that occurred in the chemical context is constant. No matter the
steps it takes to achieve this reaction, the chemical reaction is consistently the same.
References
Averill, B., & Eldredge, P. (2007). Chemistry: Principles, patterns, and applications. Upper
Saddle River, NJ: Pearson.
Bekhterev, V., & Strickland, L. H. (2017). The Law of Conservation of Energy. Collective
Reflexology,291-295. doi:10.4324/9781351327008-20