Calorimetry Experiment Assignment
Post lab
Introduction
We determined the change in enthalpy to be negative, which means energy is sendoff the system and entering the environments in the form of heat.
Calorimetry is the chemical process which is used to measure heat in chemical reaction. The apparatus used is the calorimeter. A coffee cup calorimeter is not technologically advanced but it is effective in stopping heat transfer between the system and the atmosphere. Because the cup is open to the air, this is a constant pressure measurement. Per the first law of thermodynamics, the total energy of an isolated system can neither be created nor destroyed. In other words, energy is preserved in chemical reaction.
Calorimeter will consist of two nested Styrofoam coffee cups and a plastic cover. It will use a temperature sensor armed with a thermocouple probe. There will be a hole in the plastic cover of your calorimeter for insertion of the probe. In this experiment, we are going to study about the redox reactions with coffee cup and calorimeter.
Hypothesis and Objectives
Using a coffee cup calorimeter, the heat of neutralization of HCl and NaOH is measured. From this, the enthalpy change for the neutralization of one mole of HCl can be calculated.
• Introduction to the technique of calorimetry, in which the heat is evolved or absorbed by a chemical reaction is incidental by measuring temperature vicissitudes in an insulated reaction container.
• Reaction involve strong bases and acids will produce more heat.
Methods
Following are the materials that are used in experiment.
• Coffee cup calorimeter thermometer
• Lid or parafilm
• 10 mL graduated cylinder
• HCL
• NaOH
• Water
• 250 mL beaker
Procedure
1. Set up calorimeter apparatus.
2. Measuring solution temperature before mixing.
3. Adding simultaneously HCl and NaOH to the coffee cup.
4. Measure temperature change after mixing.
5. Calculate enthalpy change.
(J. Kotz, P. Treichel, J. Townsend; Chemistry & Chemical Reactivity 7th ed. 2009)
Obtain 10 ml of cold water and get the temperature, and pour it into your calorimeter. Then do the same thing for hot water. After that, measure the final temperature when it reaches equilibrium. Use the initial and the final temperatures to measure Ccal. Now gather two 50 mL beakers, one for NaOH, and one for HCl. Use the 10-mL graduated cylinder and then add the 3 mL of HCl and 7 mL of water, measure the temperature and put it into your unfilled calorimeter. Do the same for NaOH. Then put the thermometer in and measure the exact last temperature of it.
Clean up, and do the same thing again, but with 5 mL, then 7 mL of the acid and base, to get .5 Mol and .7 Mol. Clean up your solutions, it is just NaCl and H2O, so you can solution it down the drain, if you have an extra HCl then neutralize it with sodium bicarbonate before pouring down the drain. Now calculate for the ΔHrxn as seen in the Calculations section
Reaction: NaOH + HCl --------- > NaCl + H2O
In this reaction, Sodium hydroxide react with Hydrochloric acid to produce salt and water. This is an example of neutralization reaction. The initial temperature, the final temperature and mass of solution were measured.
Enthalpy:
Heat transfer does not occur instantaneously, so using calorimeter to determine the enthalpy change requires measuring the temperature of the calorimeter contents as the change occurs.
Q = n H
H = Q/n
Result
The results indicated that when the Molar concentration of the acid-base pair enlarged, the Δq will be also increased. It also shows that ΔHrxn increased as well, which shouldn't have happened, because ΔHrxn is the ratio per mole of the enthalpy of heat, and it should be constant for the same acid-base pairs.
The neutralization reaction of hydrochloric acid with sodium hydroxide is given below:
HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l) + heat
Experiment Data Information
|
Trials
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0.3 Mol HCL and NaOH
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0.5 Mol HCL and NaOH
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0.7 Mol HCL and NaOH
|
|
C of calorimeter (J/C)
|
3.21
|
3.21
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3.21
|
|
Initial temperature (C)
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20.5
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20.0
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21.5
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Final temperature (C)
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21.5
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25.0
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26.5
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Heat Change q(J)
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-62.67
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-230.912
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-397.48
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ΔHrxn (KJ/mol)
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-2.092
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-4.6024
|
-5.678
|
Calculations:
q cold initial temp: 22.0 (C`), final temperature 29.0 (C`)
q hot initial temp: 35.5 (C`), final temperature 29.0 (C`)
equation: m x C x ΔT
q cold = 10 x 4.18 x 7.0 = 292.88 J
q hot = -271.96 J
q calculation = -20.92 J (-qcal = q cold + q hot)
equation: Ccal = (qcal)/ ΔT
Ccal = 3.124
Solve for ΔHrxn
For 0.3 Mol: q solution = 20 g x 4.18 x (23.0-22.0) = 83.68
qrxn = q solution - q calculation
qrxn = -62.76 J
ΔHrxn = qrxn/0.3 = 2.092 KJ/mol
Decision
Ideally, calorimeters should have an infinitely low lining from the reaction cavity, and infinitely high insulation on the outside to ensure that all the heat is transferred to the water, and that none leaks from the calorimeter itself. The numbers that the experiment produced show that there is a difference in the heat transferred dependent on the forte of the acid and/or base and the possessions of the metal. Although, further experiments might reveal more conclusive data on the nature of such an assumption. However, the strongest acid and strongest base appeared to have the most enthalpy change.
Conclusion
The results fail to invalidate hypothesis, but do not offer convincing results to uphold hypothesis well e.g. average heat evolved by the reaction of neutralization.
Not having the precise mass of solutions (when poured from beaker to Styrofoam cup)
Inexact quantities of reactants (due to lack of usage of volumetric measuring instruments)
Research Connection
Graphite calorimeters used in radiotherapy for cancer. The radiation therapy conveys heat and this heat is measured using the isothermal sensors in the graphite calorimeter. The reasoning behind this is so that excess radiation does not kill healthy tissue.
References
• https://web.lemoyne.edu/giunta/chm151L/calorimetry.html
• J. Kotz, P. Treichel, J. Townsend; Chemistry & Chemical Reactivity 7th ed. Instructors Edition; Brooks/Cole; 2009
• Gary L. Bertrand, retrieved from
https://web.mst.edu/~gbert/cupCal/disc.htm