Understand the form and meaning of the equilibrium constant expression. Chemical
ID: 766736 • Letter: U
Question
Understand the form and meaning of the equilibrium constant expression. Chemical reactions are usually not one-way trips from reactant to product. In fact, most chemical reactions are reversible to at least some extent. In other words, products formed by the forward reaction may react with each other to regenerate the reactants. When reactants are mixed, they will begin to react at a forward reaction rate particular to that chemical reaction. As reactants are depleted and products are formed, however, the rate of the forward reaction begins to slow, and the rate of the reverse reaction begins to increase. Eventually, the forward and reverse reaction rates will be identical. The products of the reaction are being formed at the same rate as they are being converted back to reactant, and there is no overall change in the concentrations of the reactants or the products. At this point, chemical reactions are said to be at equilibrium. Keep in mind that this is not the same as saying that the reaction has "stopped." Equilibrium is dynamic, meaning that it is a balance of continuous forward and reverse reactions. To indicate this dynamic nature of equilibrium, chemical equations of reactions with The K of the reaction N02(g) + N03(g) N205(g) is K = 2.1 times 10-20. What can be said about this reaction? At equilibrium the concentration of products and reactants is about the same At equilibrium the concentration of products is much greater than the concentration of reactants At equilibrium the concentration of reactants is much greater than that of products There are no reactants left over once the reaction reaches equilibrium Where does the equilibrium of this reaction lie? To the left To the right Neither left nor right Not enough information To understand the relationship between the equilibrium constant and rate constants. For a general chemical equation A+B C+D the equilibrium constant can be expressed as a ratio of the concentrations: If this is an elementary chemical reaction, then there is a single forward rate and a single reverse rate for this reaction, which can be written as follows: where kf and kr are the forward and reverse rate constants, respectively. When equilibrium is reached, the forward and reverse rates are equal: Thus, the rate constants are related to the equilibrium constant in the following manner: For a certain reaction, Calculate the value of the reverse rate constant, kr, given that the reverse reaction is of the same molecularity as the forward reaction. Express your answer with the appropriate units. For a different reaction, Adding a catalyst increases the forward rate constant to What is the new value of the reverse reaction constant, kT, after adding catalyst? Express your answer with the appropriate units. Yet another reaction has an equilibrium constant It is an exothermic reaction, giving off quite a bit of heat while the reaction proceeds. If the temperature is raised to 200 degree C , what will happen to the equilibrium constant? The equilibrium constant will increase. decrease. not change.Explanation / Answer
a) Kc=kf/kr ==> kr = kf/kc = 1.13*10^-2 M-2s-1 b) A catalyst has no effect on the position of the equilibrium since it increases not only the rate of forward reaction but also the rate of backward reaction. However it does help the system to reach the equilibrium faster. so no change in the equilibrium constant kr = kf/kc = 1.11*10^4 s-1 c) Decrease in the temperature of the system favors the exothermic reaction. so If the equilibrium is disturbed by increasing the temperature by adding heat, the exothermic backward reaction is not favoured and .While doing so, the concentration of 'B' decreases and a new equilibrium position is established for which the new equilibrium constant, so kc1 will be smaller decreases will be the anwer many other things from http://www.adichemistry.com/physical/equilibrium/le-chatelier/le-chatelier-principle.html
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