pls, follow the instructions. There is an example of how to do the lab I put it as an example of how my Ta wants. If you put resources cite them pls.  

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4.65E-19

3147146

0.21

																	447.1	385
471.3	415
492.2	434
501.5	472
587.5	555
667.8	673
4.28E-07	359
4.55E-07	394
4.94E-07	445
6.63E-07	625
delta E	n-initial
6.63E-34		4.65E-19	5.2091208904
c	299792458	4.37057167592519E-19	4.4939821383
2.18E-18	4.02191704132011E-19	3.9070730247
	0.21	0.22222222	2.99611587738763E-19	2.9805830097
4.37E-19	0.2004849393
4.02E-19	0.1844916074	0.1875	SQRT(1/((4.64661E-19/(2.18E-18)+.25))
3.00E-19	0.1374365081	0.1388889

Helium Spectroscopy

Helium

385 415 434 472 555 673 447.1 471.3 492.2 501.5 587.5 667.8

Millimeters

Nanometers

Rydberg Constant

Rydberg

0.2131471459528945 0.20048493926262353 0.18449160740000481 0.13743650813704733 4.6500000000000003E-19 4.3709999999999997E-19 4.0220000000000001E-19 2.9959999999999998E-19

(1/n^2-1/n^2)

Delta E

0.22222222 0.21 0.1875 0.13888890000000001 4.6500000000000003E-19 4.3709999999999997E-19 4.0220000000000001E-19 2.9959999999999998E-19

HEATSOF REACTION

CHMY 141-220

TA: Olivia Andrus

11/14/19

Introduction

As the title indicates, this lab explored the properties of the heat released from certain

reactions through recording the heat change as the reaction occurs with the use of a thermistor.

Performing these reactions demonstrated some principles of thermodynamics; including the use

of Hess’s Law, which states that the total heat change of a reaction is equal to the sum of the heat

from all the changes in the reaction (Cohen, 2019). In this lab, three different reactions were

performed: two of the reaction’s heats should, theoretically, add up to be the heat of the third

reaction, precisely demonstrating the principles of Hess’s Law. The heat of each reaction was

recorded by setting up a thermistor suspended over a styrofoam cup that was filled with the

substance that was being reacted; the heat registered by the thermistor was then recorded

graphically on a computer program and used for interpretation. Thermodynamics and Hess’s

Law can be applied to many things, from car companies, to caloric breakdown of food in the

body. Most importantly, Hess’s Law is often used for industries that use the burning of fuel for

energy; with Hess’s law, the companies can measure how much energy a fuel releases and use

the information to make efficient energy choices (Harshini, et. al. 2015).

Procedure and Observations

This lab began by setting up a Microlab experiment with a thermistor that would record

the time and temperature of the chemicals being tested. A graph was prepared using time as the

x-axis, and temperature in Celsius as the y-axis. The thermistor was set up so it was suspended

over a styrofoam cup about one-half inch from the bottom. Next, the mass of a 50 mL beaker

was taken and recorded. Two to three grams of KOH pellets were measured out and the exact

mass was taken and recorded, then placed into the beaker, and the mass of the beaker and the

pellets were taken and recorded. This beaker was set aside for the moment and 100 mL of water

was measured using a graduated cylinder and poured into the styrofoam cup. The temperature of

the water was recorded for two minutes, then, while continuing to record, the KOH pellets were

added to the water and stirred continuously; the solid KOH appeared to dissolve and the

temperature readings rose​.​ The temperature was recorded for another three minutes, making a

total of five minutes recording. After the five minutes, this solution was poured into a clean, dry

beaker and covered with a glass watch glass in order to prevent contamination. The styrofoam

cup was then rinsed out with deionized water, three times to prepare for the next reaction. The

data collected was exported to an excel file and saved.

Another two to three grams of KOH pellets were measured out and recorded, then put

into the fifty mL beaker which was also measured and recorded. A new Microlab experiment

was prepared, recording time and temperature just as before, and the thermistor was set up

suspended over the styrofoam cup again. Approximately 160 mL of 1.5 M HCl was placed into a

250 mL beaker. 100 mL of that solution was measured using a graduated cylinder and poured

into the styrofoam cup. The temperature of the HCl was recorded for two minutes, and, just as

before, the solid KOH was added stirring continuously. The temperature was recorded for an

additional three minutes, for a total of five minutes. Then, the pH of the solution was tested using

a piece of pH paper, which remained pink; this result was then recorded. The styrofoam cup was

then rinsed three times with deionized water again and prepared for the next reaction. The data

recorded was then exported to an excel file and saved.

Next, the graduated cylinder was rinsed with deionized water and fifty mL of the KOH

solution from the first part of the experiment was measured out and placed into a clean, dry fifty

mL beaker. The graduated cylinder was rinsed and dried again and fifty mL of the 1.5 M HCl

solution was measured and poured into the styrofoam cup. The thermistor was suspended in the

fifty mL beaker containing the KOH solution for two minutes, and the initial temperature was

recorded. This data was exported and saved to an excel file. The thermistor was then rinsed and

dried and a new Microlab experiment was set up. The temperature of the HCl in the styrofoam

cup was then recorded for two minutes, and just as before, after two minutes, the KOH solution

was added and stirred continuously. The temperature was recorded for an additional three

minutes for a total of five minutes. The pH of this solution was also tested with a pH paper,

which turned blue in color. This data was exported and saved to an excel file, and the solution

was disposed of.

Data

The graphs below show the data collected in all three trials of the experiment. Graph 1

shows the time vs. temperature data collected for the first reaction with water and solid KOH.

Graph 2 shows the data collected in the second reaction of the lab with HCl and solid KOH.

Graph 3 shows the data collected for the final reaction of the lab, adding the KOH created in the

first reaction to HCl. Graph 4 shows the temperature of the KOH solution that was recorded on

its own for two minutes in the third part of the lab, before being added to the HCl solution. Table

1 shows various numerical data that was either collected or calculated, that gives information

such as the heat that the reaction gives off, or the limiting reagent in the reaction. Table 2 shows

the same data as Table 1 shared from the three other groups in the lab.

Graph 1

Graph 1: Shows the data collected from the thermistor for the first reaction of the experiment,
adding solid KOH to water. The temperature is represented in Celsius on the y-axis while the
time is on the x-axis in seconds. At 120 seconds, the KOH was added, resulting in a rise in
temperature, from roughly 23 degrees Celsius to about 26. A trendline was created to best fit the
data, which has a fairly low R-squared value of 0.7588.

Graph 2

Graph 2: Shows the data collected from the thermistor for the second reaction performed, adding
solid KOH to 1.5 M HCl solution. The temperature is represented in Celsius on the y-axis while
the time is on the x-axis in seconds. At 120 seconds, the KOH was added, resulting in a rise in
temperature, from roughly 24 degrees Celsius to about 33. A trendline was created to best fit the
data, which has a fairly low R-squared value of 0.7343.

Graph 3

Graph 3: Shows the data collected from the thermistor for the third reaction performed, adding
the KOH solution from part 1 to 1.5 M HCl solution. The temperature is represented in Celsius
on the y-axis while the time is on the x-axis in seconds. At 120 seconds, the KOH solution was
added, resulting in a rise in temperature, from roughly 23 degrees Celsius to about 27. A
trendline was created to best fit the data, which has a fairly low R-squared value of 0.7116.

Graph 4

Graph 4: Shows the temperature of the KOH solution created in part 1 that was collected over
two minutes. Just as the other graphs, the temperature is on the y-axis in Celsius, and the time in
seconds on the x-axis in The temperature stayed fairly consistent, fluctuating around 25 degrees
Celsius.

Table 1

Part 1 Part 2 Part 3

mass of KOH 2.234 g mass of KOH 2.541 mass of KOH 4.46

moles of KOH 0.0398 mol moles of KOH 0.0453 moles of KOH 0.0769

mL solution 102.234 mL moles of HCl 0.15 moles of HCl 0.075

ΔT 3.157 ℃ mL of solution 102.541 mL of solution 100

Heat(J) 1320.8 pH test acidic pH test basic

Heat (J)/mole
KOH 33185.9 Limiting Reagent KOH Limiting Reagent HCl

ΔT 8.705 ΔT 3.32

Heat (J) 98.426 Heat (J) 18.77

Heat(J)/ mole of
KOH 2127.75

Heat(J)/ mole of
KOH 235.8

Percent error=

1438%

Table 1: Data collected from all three trials that included the mass of the KOH, the calculated
moles of the KOH, the mL of solution, the change in temperature, the calculated heat produced,
and the calculated heat per mole produced. Part 2 and 3’s columns are longer because they
include the calculated moles of HCl, pH test, and the calculated limiting reagents.

Table 2
Group 1

Part 1 Part 2 Part 3

Mass of KOH 3.0684 Mass of KOH 2.9217 Mass of KOH 3.1111

Moles of KOH 0.0538 Moles of KOH 0.0513 Moles of KOH 0.0555

mL of solution 103.0684 Moles of HCL 0.15 Moles of HCL 0.0075

ΔT 4.6 mL of solution 102.9217 mL of solution 100

Heat (J) 1924.64 pH test Acidic pH test Basic

Heat (J)/ Mole of
KOH 35773.98 Limiting Reagent KOH Limiting Reagent HCL

ΔT 10.6 ΔT 3.6

Heat (J) 4435.04 Heat (J) 1506.24

Heat (J)/ Mole of
KOH 86453.02

Heat (J)/ Mole of
KOH 27139.46

Percent error=

27.23%

Group 2

Part 1 Part 2 Part 3

Mass of KOH 2.75 Mass of KOH 2.32 Mass of KOH 5.5

Moles of KOH 0.049 Moles of KOH 0.041 Moles of KOH 0.098

mL of solution 102.75 Moles of HCl 0.15 Moles of HCl 0.075

ΔT 3.71 mL of solution 102.32
mL of final
solution 100

Heat (J) 1550.4 pH test acidic pH test basic

Heat (J)/mole
KOH 31632.3 Limiting reagent KOH Limiting Reagent HCl

ΔT 7.84 ΔT 2.93

Heat (J) 3279.3 Heat (J) 612.7

Heat (J)/mole
KOH 79307.1 Heat (J)/mole KOH 6252

Percent error=

52.2 %

Group 3

Part 1 Part 2 Part 3

mass of KOH 2.5 mass of KOH 2.71 Mass of KOH 5.04

moles of KOH 0.0449 moles of KOH 0.0483 Moles of KOH 0.0898

ml of solution 100.67 Moles of HCl 0.15 Moles of HCl 0.075

ΔT 3.58 mL of solution 101.51
mL of final
solution 101.53

heat(J) 1497.87 pH test acidic pH test basic

Heat(J)/mol KOH 33360.19 Limiting reagent KOH Limiting Reagent HCl

ΔT 10.18 ΔT 0.351

Heat (J) 4260.57 Heat (J) 146.858

Heat (J)/mole
KOH 88210.501 Heat (J)/mole KOH 1635.394

Percent error=

60.32%

Table 2: Shows the same data as displayed in Table 1 for three additional groups who performed
the lab.

Data Analysis and Calculations

Moles of KOH=
mass of KOH(g)

Molar Mass of KOH(g/mol)

= ​0.0453 moles of KOH2.541g56.108g/mol (1)

(volume of liquid (mL)) + (mass of solid(g)) = ​volume of solution (mL)

(​100​mL H​2​O) + (​2.541​g KOH) = ​102.541 ​mL of solution (2)

(final temp.) – (initial temp.) = ​change in temp.​℃

(​32.965​℃) – (​24.26​℃) = ​8.705​℃ (3)

Molarity of HCl ・Volume(L)​= Moles of HCl

1.5​M ・​0.1​L= ​0.15 moles of HCl (4)

(moles of KOH)(mole ratio of KOH:H​2​O from equation)(molar mass of H​2​O)=​ mass of H​2​O

(0.0453​mol KOH​)( )(18.016​g/mol​)= 0.816 grams of H​2​O (5)
1 mol H2O
1 mol KOH

(mass of H​2​O)(specific heat(constant))(change in temperature(℃))= ​Heat(J)

(2.7024​g H​2​O​)(4.184)(8.705​℃)= ​98.426​J (6)

= Enthalpy
Heat(J)

mole KOH

= 2172.76 ​J/mol98.426J0.0453mol KOH (7)

Theoretically: ​(Enthalpy of reaction 1) + (Enthalpy of reaction 3)= ​Enthalpy of reaction 2

(33185.9​J/mol​) + (235.8​J/mol) ​≠ 2172.76​J/mol
Experimentally: (33185.9​J/mol) + ​(235.8​J/mol​) = 33421.7​J/mol ​ (8)

theoretical value
experimental value−theoretical value| | 00 error × 1 = %

% error2172.76J /mol
(33421.7J /mol)−(2172.76J /mol)| |

00 438× 1 = 1 (9)

The temperature change that was recorded for each of the reactions shows that each

reaction rose in temperature, indicating that the reaction gave off heat that was then absorbed and

registered by the thermistor, making them all, exothermic reactions. The graphs of the reactions

all resemble each other in appearance: a fairly constant line at one temperature, then an almost

vertical rise in temperature at the two minute mark, when the KOH was added, before abruptly

flattening off again for the remaining two minutes. However, they differ in both their initial

temperatures, as well as their magnitude of change. For example, the first reaction began at a

steady temperature of about 23 degrees Celsius, and rose to a temperature of about 26 degrees

Celsius. Whereas the second reaction began at a temperature around 24 degrees Celsius and rose

to approximately 33 degrees Celsius; becoming the experiment’s largest difference. Finally, the

third reaction began, again, around 23 degrees and rose to about 27 degrees Celsius.

When compared to the other groups data, the amount of KOH used, correlated to the

amount of heat derived from the reaction. Because our results were so vastly different from the

other group’s data, these approximations were calculated only using their data. It appears that for

the first two reactions, the higher mass of KOH used, resulted in a greater amount of heat being

released from the reaction; with the average ratio of grams of KOH to heat released, being

approximately 1.7g/1000J for the first reaction and about 0.67g/1000J. In regard to the third

reaction, the mass of KOH seemed to have no significant effect on the amount of heat released,

as the ratios differ from 2g/1000J in the first group, and 9g/1000J in the second group, to

34g/1000J in the third group.

Theoretically, based on Hess’s Law, the second reaction’s enthalpy should be the sum of

the first and third reaction’s enthalpy. This law seems proven by looking at the data from the

other three groups, all their percent error values coming in at under 100 percent. However, when

looking at the experimental data from the experiment we performed, Hess’s Law cannot be

accepted from this experiment with a percent error as high 1438 percent.

The acidity test that was performed and recorded for the second and third reactions was

significant to defining which reactant was the limiting reagent, confirming the values that were

then calculated using the amount of KOH used. The limiting reagent for the second reaction was

the KOH because the solution was acidic, meaning there was more of the acidic HCl in the

solution; and the limiting reagent for the third reaction was HCl because the solution was basic,

meaning there was more of the basic KOH in the solution.

Conclusion

The intention of this lab was to demonstrate the properties of temperature change in

chemical reactions and how that relates to heat and thermodynamics. These principles were

effectively conveyed using the thermistor and Microlab to record in a visually accessible manner

which made clear a significant temperature change in reactions that, visually, don’t make the

most dramatic transformations. Hess’s Law was applied using the enthalpies, calculated from the

heat released in the reaction. While the concept of Hess’s law was demonstrated in terms of

theoretical values in this lab, the calculated results did not support the law, yielding a 1438

percent error.

This extremely high value is likely due to a number of things that could have happened

during the experiment. For example, the difference in initial mass of KOH could have caused a

discrepancy in the heat release values, as was mathematically discovered, the amount of KOH

has a relationship with the heat released that is not necessarily always consistent. Additionally, a

reaction could have lost more heat than was recorded by the thermistor, particularly in reaction

two, where the calculated heat released made the least sense. It is also likely that the KOH did

not completely dissolve in the solution, meaning that the full chemical reaction did not occur,

making the heat that was produced a result of something other than the full intended reaction.

And although a watch glass was placed over the aqueous KOH in order to prevent

contamination, it is possible that that solution became contaminated while sitting, which would

alter the results of the third reaction.

The heat values collected for each part of the experiment went in descending order, the

first reaction producing the most heat, and the third producing the least. However, based on the

chemical equations of the reactions, part two produces the same products as the solution made in

part one, combined with the HCl; meaning that part two is essentially a combination of parts one

and three. Because of this chemical relationship, Hess’ Law states that the heat values of parts

one and three should add up to be the heat value of part two. Meaning that the descending heat

values from one to three would mathematically make this impossible, proving, as was stated

above, that Hess’ Law is not supported by the data collected.

References

Cohen, S. (2019, September 30). Hess’s Law. Retrieved from

https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook
_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Thermodynamics
/Thermodynamic_Cycles/Hess’s_Law.

Harshini, M., & Acacia, C. (2015, December 3). Enthalpy of Reaction and Hess’s Law. Retrieved

from https://sites.google.com/site/experiment6enthalpy/home.