Exergonic Reaction Lab

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Background The cell is filled with a myriad of chemical reactions happening simultaneously that work to ensure its survival. Some of these reactions are exergonic, meaning they release energy and occur spontaneously. They occur spontaneously because the products of the reaction have a lower free energy than the reactants. The free energy of a reaction is how much of the energy in the reaction's system is free to do work. When the reaction occurs, the free energy that was stored in the reactants is released into the surroundings. Gibbs free energy (∆G) is a measure of the difference in free energy between products and reactants when the reaction occurs at a constant temperature and pressure, and is found using the following equation:

∆G = …show more content…
120

180
Final Burette Reading (mL)
42.1
29.1
32.6
36.1
39.7
Inital Burette Reading (mL)
38.5
25.6
29.1
32.6
36.1
Volume KMnO4 Used (mL)
3.8
3.5
3.5
3.5
3.6
#Moles KMnO4 Used (moles)
4.8*10-4
4.4*10-4
4.4*10-4
4.4*10-4
4.5*10-4
#Moles H2O2 in Solution after Rxn (moles)
1.2*10-3
1.1*10-3
1.1*10-3
1.1*10-3
1.2*10-3
#Moles H2O2 Used During Rxn (moles)
0
1.0*10-4
1.0*10-4
1.0*10-4
0

Part D Calculations

Volume KMnO4 Used
Final Burette Reading-Initial Burette Reading
#Moles KMnO4 Used
Volume KMnO4 Used * (1g solution/1 mL solution) * (2g KMnO4/100g solution) * (1 mol KMnO4/158.04g)
#Moles H2O2 in Solution after Rxn
#Moles KMnO4 Used * (5 mol H2O2/2 mol KMnO4)
#Moles H2O2 Used During Rxn
Baseline Number of Moles of H2O2 Present in Solution - #Moles H2O2 in Solution after Rxn

Questions

4. a: (0.0 mol - 0.0 mol))/(10 sec - 0 sec) = 0 mol/sec b: (1.0*10-4 mol - 0.0 mol)/(30 sec - 10 sec) = 5.0*10-6 mol/sec c: (1.0*10-4 mol - 1.0*10-4 mol)/(60 sec - 30 sec) = 0 mol/sec d: (1.0*10-4 mol - 1.0*10-4 mol)/(120 sec - 60 sec) = 0 mol/sec e: (0.0mol - 1.0*10-4 mol)/(180 sec - 120 sec) = -1.7*10-6 …show more content…
The reaction rate before then (in the interval between 10 and 30 seconds) suggests that the reaction should continue at a constant rate, but the reaction instead stops completely. The reaction rate should taper off to zero before stopping as substrate concentration decreases, not stop abruptly The percent error of this incongruity is calculated as follows:
((5.0*10-6 mol/sec - 0 mol/sec))/5.0*10-6 mol/sec) * 100 = 100% This error likely stemmed from the lack of precision in the burette used. The burette only measured up to the hundreth place, requiring us to round up or down based off of sight alone. The reaction was still occurring, but it was at such a slow rate to begin with that the changes in substrate concentration were too small for us to have an accurate reading on the burette. The second error is the reaction reversing in the interval between 120 seconds and 180 seconds. The number of moles of H2O2 in solution goes from 1.1*10-3 mol to 1.2*10-3 mol, an amount equal to the baseline number of moles of H2O2. In other words, the reaction changes from having used 1.0*10-4 moles of H2O2 to having used none at all. This data shows the reaction spontaneously reversing, which can never occur in what is already a spontaneous reaction. The percent error of this mistake is calculated as
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