Calorimetry used to calculate the enthalpy of ...
Calorimetry used to calculate the enthalpy of neutralization reactions November 18, 2013 Joshua Fernandez ID#: 2051 5215 Rachel Dillman Elizabeth Boyd Section 001
Introduction: Calorimetry is the science of measuring the change in heat in physical or chemical reactions. This is determined through a device called a calorimeter. A calorimeter is isolated from its surroundings, as to only find out the temperature inside. It works by two chemicals being mixed in the calorimeter, reacting together, and a thermometer being placed beforehand in order to measure the change in heat inside the calorimeter. This is not a sealed system; therefore the internal pressure has to equal the atmospheric pressure. (Hansen and Russell 2006). If this is the case, the final and initial pressures would have to be the same as well. The symbol, q, represents the gain or loss of heat in a system. Ergo, because the pressures do not change within the reaction, q, and ∆H, which represents the enthalpy change, will be the same (Hansen and Russell 2006). The lab also deals with neutralization reactions. A neutralization reaction is the reaction between an acid and base which results in the forming of a salt and water. This lab specifically deals with strong electrolytes. Strong electrolytes completely disassociate when placed in solution (Andriola, Singh, Lewis and Yu 2010). In this lab, the neutralization reactions of strong electrolytes will produce q= -55.90KJ/mol of the hydrogen ion (Thauer 1998). As previously stated, q equals the enthalpy change; therefore the enthalpy change is also -55.90 KJ/mol of the hydrogen ion (Thauer 1998). There is a negative sign present, which means the reaction is exothermic: heat has been released. Finally, the lab discusses neutralization reactions with weak electrolytes. Weak electrolytes only partially disassociate into ions (Andriola, Singh, Lewis and Yu 2010). That means the q and enthalpy change for the reaction will depend on the electrolyte itself, and can either be exothermic or endothermic. Therefore, the calculation for the heat of the reaction will help with distinguishing between strong and weak electrolytes.
Experimental Procedure: “The experimental procedure used for this experiment was outlined in the CHEM 120L lab manual, experiment #4. The experiment was done with deviation. The concentrations of the chemicals used in the lab were different from those in the lab manual.) Experimental Observations: Part A: The neutralization reaction of NaOH and HCL Trial #1 Every Second(C)
Every 10 Seconds(C)
Every 30 Seconds(C)
27.4
38.3
37.5
29.3
38.3
37.2
32.5
38.1
37.1
35.7
38.0
37.1
38.1
38.1
37.0
38.2
37.0 37.0 37.1 36.9 36.9
Part A: The neutralization reaction of NaOH and HCL Trial #2 Every Second(C)
Every 10 Seconds(C)
Every 30 Seconds(C)
26.2
35.8
35.0
28.4
35.1
35.0
30.1
35.1
35.0
34.3
35.1
35.0
35.1
35.1
34.9
35.1
34.9 34.9 34.9 34.9 34.9
Part B: The neutralization reaction of NaOH and HNO3 Trial #1 Every Second(C)
Every 10 Seconds(C)
Every 30 Seconds(C)
25.1
40.1
39.9
30.2
40.0
39.9
31.3
39.9
39.8
34.8
39.9
39.8
38.1
39.9
39.6
39.9
39.6 39.1 38.9 38.9 38.9
Part B: The neutralization reaction of NaOH and HNO3 Trial #2 Every Second(C)
Every 10 Seconds(C)
Every 60 Seconds(C)
25.5
39.8
39.2
30.3
39.9
39.4
33.0
39.9
39.3
37.2
39.8
39.1
39.6
39.8
38.9
39.8
38.9 38.9 38.9 38.9 38.9
Part C: The neutralization reaction of NaOH and Phenol Trial #1 Every Second(C)
Every 10 Seconds(C)
Every 60 Seconds(C)
26.2
28.1
28.1
27.1
28.2
28.1
27.8
28.2
28.2
27.9
28.3
28.1
28.3
28.0
28.0
28.1
28.0 28.0 28.1 28.0 28.1
Part C: The neutralization reaction of NaOH and Phenol Trial #2 Every Second(C)
Every 10 Seconds(C)
Every 60 Seconds(C)
25.2
27.9
27.8
26.2
27.8
28.1
27.1
28.0
27.9
27.9
27.8
27.8
28.1
27.9
27.9
27.8
27.8 27.9 27.9 27.9 27.9
Part D: The neutralization reaction of NaOH and an unknown concentration of HCL Trial #1 Every Second(C)
Every 10 Seconds(C)
Every 60 Seconds(C)
26.1
37.1
37.0
28.6
37.0
36.9
30.3
36.9
36.9
34.7
37.0
36.8
36.9
37.0
36.9
37.0
36.8 36.7 36.8 36.3 36.1
Part D: The neutralization reaction of NaOH and an unknown concentration of HCL Trial #1 Every Second(C)
Every 10 Seconds(C)
Every 60 Seconds(C)
28.5
37.1
37.0
28.8
37.2
36.9
30.6
37.0
37.0
33.4
37.1
36.9
35.1
37.2
36.9
37.1
37.0 36.7 36.9 36.8 36.8
Sample Calculation for Part A, B and C Part A:
Part B:
Part C:
Part D:
Summary Table of the four parts of the lab: Part
Trial
Base (M)
Acid (M)
∆T (C)
Moles
q (KJ)
q/mol
H2O A
1
2.075
1.778
10.9
0.0711
-4.10
-57.7
2
2.075
1.778
10.8
0.0711
-4.02
-56.5
10.9
0.0.711
-4.06
-57.1
Average: B
1
2.075
2.322
15.0
0.0929
-5.65
-60.8
2
2.075
2.322
14.4
0.0929
-5.42
-58.3
14.7
0.0929
-5.54
-59.6
Average: C
Average:
1
2.075
0.5115
3.1
0.0256
0.817
31.9
2
2.075
0.5115
3.0
0.0256
0.791
30.9
3.05
0.0256
0.804
31.4
D
1
2.075
?
11.0
0.125
-4.60
2
2.075
?
11.3
0.125
-4.73
11.2
0.125
-4.67
Average:
Discussion: In this lab, we used a coffee cup calorimeter to find the average time, heat change of the reaction, and the heat change per mol of the reaction. This was done so that an unknown concentration of HCL could be determined. The average time was calculated through the graph. The highest recorded time subtracted from the lowest recorded time gives us the change in temperature. The heat change of the reaction was determined by multiplying the change in temperature, the specific heat of water, which is 4.184 J/cal C, and the mass of the two solutions. The mass was determined through the density. One gram of water is equal to one milliliter of water; ergo ninety milliliters would give us ninety grams of water. For part A, the heat lost due to the reaction was q= -21.9 KJ/mol of water. The tabulated value in the manual is q= -55.90 KJ/mol. The calculated value is lower than the tabulated value. For part B, the calculated change in heat per mol was q= -29.6 KJ/mol. This again is lower than then tabulated value. The above reactions both involve strong electrolytes as both HCL and HNO3 are strong acids, and they disassociate completely. For part C, the calculated value of the heat change per mol was 29.8 KJ/mol. The tabulated change in enthalpy for phenol is q= 25.3 KJ/mol. The calculated value is slightly higher than the recorded value in the manual.
Possible errors that could have occurred are the readings of the temperatures. It is possible that when the temperatures were being read out, that value could either be too high, or too low resulting in an enthalpy change that would differ than correct readings. As well, with regards to the thermometer, all the heat that is released will not show up on the thermometer. Some of the heat would be lost to the room. It is also possible that the actual recorded temperature is inaccurate. Due to the fact that heat is released during the experiment, the released heat is going to heat the bottom of the thermometer, as well as the top and sides, therefore giving a value which would be higher than an accurate temperature recording. Conclusion: The purpose of this lab was to use a calorimeter to find out the heat changes in four parts of the experiment. These values were then used to calculate the enthalpy change of the reaction, and the change per mol. The objectives were not met for parts A and B as the enthalpies recorded for both parts are quite different than the tabulated value. For part C, the objective was met with regards to phenols enthalpy change, as the tabulated value and calculated value are close to one another. For part D, 40 ml of HCl were given to us, with an unknown concentration. Using the same methods for parts A, B, and C, the moles of water can be determined. For HCl unknown #4, with the value of q being determined for Part D, and the value of q from the entire reaction, we can obtain the amount of moles of water. That value equals to the moles of HCl. By divining that number by the volume of HCl, we get 2.095 mol/L as the unknown concentration of HCL in Part D. The lab is quite effective as it helps students understands thermodynamics better, and putting it in a lab setting makes it easier to understand.
However, some things could be improved. For instance, when measuring the temperature change of the reaction after the reactants have been mixed or every second, it is highly unlikely that students are going to be able to do that with accuracy. Using a thermometer that digitally provides these numbers may make it easier for students to record their findings. Regarding the reliability of the lab, it is quite easy to perform, and there are not that much room for error. However, the lab could be made more reliable through better explanation and equipment. Through smaller graduated cylinders, and the digital thermometers, the lab could be more reliable for students, and teach them the importance of Calorimetry more efficiently.
References: Department of Chemistry 2013 CHEM 120L laboratory manual fall 2013. University of Waterloo, Waterloo. Pp 52-58
Hansen and Russell (2006). Which calorimeter is best? A guide for choosing the best calorimeter for a given task. Thermochimica Acta 450 (2006) 71–72
Thauer (1998). Biochemistry of methanogenesis: a tribute to Marjory Stephenson. Microbiology (1998), 144, 2377-2406
Introduction: Calorimetry is the science of measuring the change in heat in physical or chemical reactions. This is determined through a device called a calorimeter. A calorimeter is isolated from its surroundings, as to only find out the temperature inside. It works by two chemicals being mixed in the calorimeter, reacting together, and a thermometer being placed beforehand in order to measure the change in heat inside the calorimeter. This is not a sealed system; therefore the internal pressure has to equal the atmospheric pressure. (Hansen and Russell 2006). If this is the case, the final and initial pressures would have to be the same as well. The symbol, q, represents the gain or loss of heat in a system. Ergo, because the pressures do not change within the reaction, q, and ∆H, which represents the enthalpy change, will be the same (Hansen and Russell 2006). The lab also deals with neutralization reactions. A neutralization reaction is the reaction between an acid and base which results in the forming of a salt and water. This lab specifically deals with strong electrolytes. Strong electrolytes completely disassociate when placed in solution (Andriola, Singh, Lewis and Yu 2010). In this lab, the neutralization reactions of strong electrolytes will produce q= -55.90KJ/mol of the hydrogen ion (Thauer 1998). As previously stated, q equals the enthalpy change; therefore the enthalpy change is also -55.90 KJ/mol of the hydrogen ion (Thauer 1998). There is a negative sign present, which means the reaction is exothermic: heat has been released. Finally, the lab discusses neutralization reactions with weak electrolytes. Weak electrolytes only partially disassociate into ions (Andriola, Singh, Lewis and Yu 2010). That means the q and enthalpy change for the reaction will depend on the electrolyte itself, and can either be exothermic or endothermic. Therefore, the calculation for the heat of the reaction will help with distinguishing between strong and weak electrolytes.
Experimental Procedure: “The experimental procedure used for this experiment was outlined in the CHEM 120L lab manual, experiment #4. The experiment was done with deviation. The concentrations of the chemicals used in the lab were different from those in the lab manual.) Experimental Observations: Part A: The neutralization reaction of NaOH and HCL Trial #1 Every Second(C)
Every 10 Seconds(C)
Every 30 Seconds(C)
27.4
38.3
37.5
29.3
38.3
37.2
32.5
38.1
37.1
35.7
38.0
37.1
38.1
38.1
37.0
38.2
37.0 37.0 37.1 36.9 36.9
Part A: The neutralization reaction of NaOH and HCL Trial #2 Every Second(C)
Every 10 Seconds(C)
Every 30 Seconds(C)
26.2
35.8
35.0
28.4
35.1
35.0
30.1
35.1
35.0
34.3
35.1
35.0
35.1
35.1
34.9
35.1
34.9 34.9 34.9 34.9 34.9
Part B: The neutralization reaction of NaOH and HNO3 Trial #1 Every Second(C)
Every 10 Seconds(C)
Every 30 Seconds(C)
25.1
40.1
39.9
30.2
40.0
39.9
31.3
39.9
39.8
34.8
39.9
39.8
38.1
39.9
39.6
39.9
39.6 39.1 38.9 38.9 38.9
Part B: The neutralization reaction of NaOH and HNO3 Trial #2 Every Second(C)
Every 10 Seconds(C)
Every 60 Seconds(C)
25.5
39.8
39.2
30.3
39.9
39.4
33.0
39.9
39.3
37.2
39.8
39.1
39.6
39.8
38.9
39.8
38.9 38.9 38.9 38.9 38.9
Part C: The neutralization reaction of NaOH and Phenol Trial #1 Every Second(C)
Every 10 Seconds(C)
Every 60 Seconds(C)
26.2
28.1
28.1
27.1
28.2
28.1
27.8
28.2
28.2
27.9
28.3
28.1
28.3
28.0
28.0
28.1
28.0 28.0 28.1 28.0 28.1
Part C: The neutralization reaction of NaOH and Phenol Trial #2 Every Second(C)
Every 10 Seconds(C)
Every 60 Seconds(C)
25.2
27.9
27.8
26.2
27.8
28.1
27.1
28.0
27.9
27.9
27.8
27.8
28.1
27.9
27.9
27.8
27.8 27.9 27.9 27.9 27.9
Part D: The neutralization reaction of NaOH and an unknown concentration of HCL Trial #1 Every Second(C)
Every 10 Seconds(C)
Every 60 Seconds(C)
26.1
37.1
37.0
28.6
37.0
36.9
30.3
36.9
36.9
34.7
37.0
36.8
36.9
37.0
36.9
37.0
36.8 36.7 36.8 36.3 36.1
Part D: The neutralization reaction of NaOH and an unknown concentration of HCL Trial #1 Every Second(C)
Every 10 Seconds(C)
Every 60 Seconds(C)
28.5
37.1
37.0
28.8
37.2
36.9
30.6
37.0
37.0
33.4
37.1
36.9
35.1
37.2
36.9
37.1
37.0 36.7 36.9 36.8 36.8
Sample Calculation for Part A, B and C Part A:
Part B:
Part C:
Part D:
Summary Table of the four parts of the lab: Part
Trial
Base (M)
Acid (M)
∆T (C)
Moles
q (KJ)
q/mol
H2O A
1
2.075
1.778
10.9
0.0711
-4.10
-57.7
2
2.075
1.778
10.8
0.0711
-4.02
-56.5
10.9
0.0.711
-4.06
-57.1
Average: B
1
2.075
2.322
15.0
0.0929
-5.65
-60.8
2
2.075
2.322
14.4
0.0929
-5.42
-58.3
14.7
0.0929
-5.54
-59.6
Average: C
Average:
1
2.075
0.5115
3.1
0.0256
0.817
31.9
2
2.075
0.5115
3.0
0.0256
0.791
30.9
3.05
0.0256
0.804
31.4
D
1
2.075
?
11.0
0.125
-4.60
2
2.075
?
11.3
0.125
-4.73
11.2
0.125
-4.67
Average:
Discussion: In this lab, we used a coffee cup calorimeter to find the average time, heat change of the reaction, and the heat change per mol of the reaction. This was done so that an unknown concentration of HCL could be determined. The average time was calculated through the graph. The highest recorded time subtracted from the lowest recorded time gives us the change in temperature. The heat change of the reaction was determined by multiplying the change in temperature, the specific heat of water, which is 4.184 J/cal C, and the mass of the two solutions. The mass was determined through the density. One gram of water is equal to one milliliter of water; ergo ninety milliliters would give us ninety grams of water. For part A, the heat lost due to the reaction was q= -21.9 KJ/mol of water. The tabulated value in the manual is q= -55.90 KJ/mol. The calculated value is lower than the tabulated value. For part B, the calculated change in heat per mol was q= -29.6 KJ/mol. This again is lower than then tabulated value. The above reactions both involve strong electrolytes as both HCL and HNO3 are strong acids, and they disassociate completely. For part C, the calculated value of the heat change per mol was 29.8 KJ/mol. The tabulated change in enthalpy for phenol is q= 25.3 KJ/mol. The calculated value is slightly higher than the recorded value in the manual.
Possible errors that could have occurred are the readings of the temperatures. It is possible that when the temperatures were being read out, that value could either be too high, or too low resulting in an enthalpy change that would differ than correct readings. As well, with regards to the thermometer, all the heat that is released will not show up on the thermometer. Some of the heat would be lost to the room. It is also possible that the actual recorded temperature is inaccurate. Due to the fact that heat is released during the experiment, the released heat is going to heat the bottom of the thermometer, as well as the top and sides, therefore giving a value which would be higher than an accurate temperature recording. Conclusion: The purpose of this lab was to use a calorimeter to find out the heat changes in four parts of the experiment. These values were then used to calculate the enthalpy change of the reaction, and the change per mol. The objectives were not met for parts A and B as the enthalpies recorded for both parts are quite different than the tabulated value. For part C, the objective was met with regards to phenols enthalpy change, as the tabulated value and calculated value are close to one another. For part D, 40 ml of HCl were given to us, with an unknown concentration. Using the same methods for parts A, B, and C, the moles of water can be determined. For HCl unknown #4, with the value of q being determined for Part D, and the value of q from the entire reaction, we can obtain the amount of moles of water. That value equals to the moles of HCl. By divining that number by the volume of HCl, we get 2.095 mol/L as the unknown concentration of HCL in Part D. The lab is quite effective as it helps students understands thermodynamics better, and putting it in a lab setting makes it easier to understand.
However, some things could be improved. For instance, when measuring the temperature change of the reaction after the reactants have been mixed or every second, it is highly unlikely that students are going to be able to do that with accuracy. Using a thermometer that digitally provides these numbers may make it easier for students to record their findings. Regarding the reliability of the lab, it is quite easy to perform, and there are not that much room for error. However, the lab could be made more reliable through better explanation and equipment. Through smaller graduated cylinders, and the digital thermometers, the lab could be more reliable for students, and teach them the importance of Calorimetry more efficiently.
References: Department of Chemistry 2013 CHEM 120L laboratory manual fall 2013. University of Waterloo, Waterloo. Pp 52-58
Hansen and Russell (2006). Which calorimeter is best? A guide for choosing the best calorimeter for a given task. Thermochimica Acta 450 (2006) 71–72
Thauer (1998). Biochemistry of methanogenesis: a tribute to Marjory Stephenson. Microbiology (1998), 144, 2377-2406
