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CHM-120-Experiment 5 report.docx
CHM-120-Experiment 5 report.docx

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University of Toronto Mississauga
Judith C Poe

P a g e | 1 Introduction: The purpose of the experiment was to find the rate constant and the activation energy of reaction between a bidentate ligand, 1,10-phenanthroline and ferrous ions in an acidic solution which forms a iron (II) cation. When 1,10-phenanthroline is present in acid, its dibasic property allows it to act as a base and it gets is protonated. Also, Arrhenius equation was used in calculating the activation energy where ‘k’ is the rate constant, A is the pre-exponential factor or the frequency factor, EA is the activation energy, R is the universal gas constant and T is the Kelvin temperature. Activation energy is the minimum energy that must be input to a chemical system, containing potential reactants, in order for a chemical reaction to occur. The rate of a reaction, which is directly related to the activation energy, can be defined as the change in concentration of the reactants and products over time and when the concentration of the reactants is reduced by half of its initial concentration; it is termed as the half-life of the compound. Experimental Method: 1  Refer to Lab Manual P a g e | 2 Collection of data:  Refer to the attached data sheet Results and Calculation: P ART A – D ETERMINING THE RATE CONSTANT AT 30°C Table – 1: Calculations from experimental data Time (seconds) Optical Density Time (min) (1 min = 60 seconds) (at 510 nm) 11.58 694.8 1.07 0.0677 21.54 1292.4 0.953 -0.0481 30.3 1818 0.838 -0.177 43.39 2603.4 0.753 -0.284 51.09 3065.4 0.69 -0.371 62.1 3726 0.6 -0.511 71.23 4273.8 0.555 -0.589 81.01 4860.6 0.48 -0.734 92.04 5522.4 0.426 -0.853 102.49 6149.4 0.379 -0.970 120.29 7217.4 0.325 -1.124 Rate constant at 30°C 0.2 0 -0.2 0 1000 2000 3000 4000 5000 6000 7000 8000 -0.4 -0.6 ln O.D y = -0.000185x + 0.1862 -0.8 R² = 0.9979 -1 -1.2 -1.4 Time (s) Figure – 1: The above graph represents the relation between ln O.D and time where ln O.D is dependent on time. The slope of the graph represents the –k in the following derivation which is essentially the rate constant of the reaction P a g e | 3 The rate law for the overall reaction observed in this experiment can be written as [ ] [ ] Integrating both sides of the equation, the following is obtained [ ] [ ] ∫ ∫ [ ] [ ] [ ] [ ] The rate constant can then be determined using the integrated first-order rate law which states that [ ] [ ] The concentration of can be related to the measured absorbance through the beer lambert law. [ ] where O.D is the optical density (absorbance), [Fe] is concentration of the solute in mol/L, b is the path length of the sample in cm, and is the molar extinction coefficient in L/mol cm. By rearranging the equation, [Fe] can be expressed as [ ] Replacing [Fe] in the integrated rate law, the following is obtained Rearranging this: P a g e | 4 Therefore, which represent an equation of a line and by taking the slope of the -4 -1 line of best fit, the rate constant of the reaction is found to be 1.85 x 10 Sec . P ART B – D ETERMINING THE ACTIVATION ENERGY The rate constant of a chemical reaction can be found by applying Arrhenius equation By taking natural logarithm on both sides, This equation is of the form Y = mX + B where Y represents and X represents . The slope ‘m’ is equal to and is the y-intercept, B. In order to find the value of K, the half-life timings that were recorded during the experiment were used. [ ]and it can also be written as a rate law [ ] By equating those two equat
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