The Analysis of Thermodynamics and Kinetics - Assignment Example

Questions and Answers Compare and contrast thermodynamics and kinetics as they pertain to organic transformations. In any chemical reaction there is always a thermodynamic and kinetic aspect feature. In kinetic reaction there is always a constant that is responsible of moving forward the reaction. During any reaction free energy is always emitted. This is the thermodynamic mass. Kinetics defines a reaction rate and time taken to arrive at equilibrium while thermodynamics provides details about the products obtained from equilibrium of a reaction. In organic transformations, a kinetic reaction is more stable at its reactant state. At this state, injection of energy is needed to shift the reaction. The shifting takes place from a stable state to a state where it converts and reacts to conform to other products. In contrary, thermodynamic reactions are more stable in a product’s state. This is as a result of instant occurrence of the reaction that causes shifts in the reaction without injection of any energy. Consequently, a substance whose stability is kinetic would crave to remain in the reactant form. Thermodynamically stable substances need energy for conversion from products to reactants unlike kinetic which needs the energy to shift a reaction forward. It can be therefore concluded that thermodynamic and kinetic reactions uses energy for different purposes. For instance, thermodynamic reactions need energy to move from an opposite state compared to kinetic reactions that required energy to shift forward. 2. Draw the mechanism and all possible products for A simple format for the mechanism Applying the above concept will help you to draw the mechanism as below. Termination overall reaction 3. What type of reaction is this? Radical reaction. 4. What is the major organic product for the reaction, please explain why in details? 2-bromo-2-methylbutane The reason behind this is that in the radical halogenations, bromine is more selective but less reactive than chlorine. Consequently, in case there is a formation of a radical at one chiral centre, then the product will be racemic. The process shows that the radical is planar having equal forces. Bromine sticks itself to a tertiary carbon of degree 3 to structure into a main product. A radical of bromine adds a more stable carbon of degree three to alkanes. 5. Using the bond energies posted or in the textbook, calculates the ?H° for the reactions providing each product above. Do these values support your answer in question? What other factors must be taken into account? Initiation Br-Br 2Br ?H°=192 k j/mol From the above reactions, 1) ?H°= ? products- ? reactants = (368+343)- 343 = 368 Kj/mol 2) ?H°= ? products- ? reactants = 272 -(343 + 192) = -263Kj/mol Overall enthalpy = 368- 263 =+105Kj/mol Second product 3. ?H°? products- ? reactants (343+368) – (343) = 368 kj/mol 4. ?H°= ? products- ? reactants = (272) – (343+192) = -263 Kj/mol Overall= 368 – 263= 105 Kj/mol The other product in this level of propagation reaction repeats itself. This confirms that the ?H°= ? products- ? reactants remains constant showing that the major organic product is that of question 4 above. Since bromine experience an endothermic reaction, weakly bounded hydrogens are only removed by bromine from carbon atoms they are bonded to. The reaction between 2 – methylbutane and bromine mostly gives 2 – bromo – 2 – methylbutane and a few secondary bromides without primary bromides. The other factors that must be taken into account are pressure, temperature and catalyst. Temperature affects this reaction if it is either decreased or increased. If temperature of this reaction is increased, the rate of this reaction increases and if it is lowered the rate of reaction decreases. A catalyst can either increase or decrease reaction depending on the type. There are those catalysts that slow down reaction rate and there are those that increases reaction rate. Lastly, for enthalpy to occur there should be constant pressure. There pressure must remain constant in this reaction. 6. Assuming enthalpy is the only determining factor, which direction does this reaction favor? Enthalpy is energy associated to thermodynamics or heat loss energy. It is internal and therefore will trigger thermodynamic reaction which uses this energy to convert products to reactants. Keq < 1 the reaction will be faster towards the left. Therefore, the direction of the reaction will be to the left. 7. What is the approximate ratio of products (right) to reactants (left). 452: 46: 2: 1 or (90.3%: 9.1%: 0.4%: 0.2%) 8. What is the Keqfor this reaction? Keq = ]=] = -4.9994 9. Write an expression for the rate of this reaction and in what order is the rate? An overall rate of reaction of a process involving chains comprises three stages. The three phases are propagation, termination and initiation. Analysis is carried out using an approximation of steady states of radical intermediates. d [X]/dt=d[Z]/dt=0 Radicals’ concentration is always very low. In spite of high termination of kinetic constant, the propagation stage that has a rate constant that is low can race with termination. Overall reaction rate hence becomes propagation step rate: Rate = [Z]. [] = [X]. [Y-Z] Following approximation of the propagation steps should continue with an equal rate. Using substitution of radical C concentration, the end results are: Rate = . = where X= Br Y is H Br and Z is CHCHCH3CH2CH3 10. Draw a reaction coordinate energy diagram for the reaction above for the formation of the major product. Make sure to label and clearly illustrate ?G° and ?G‡. Works Cited Greenwood, Norman N. Earnshaw, Alan. Chemistry of the Elements (2nd ed.)199. Print Roberts, John D. and Caserio, Marjorie C. Basic Principles of Organic Chemistry, second edition., Menlo Park, W. A. Benjamin, Inc. 1977. Print Read More