о Concentration 12 10 о Concentration 2 2AB = A2 + B2 Select the graph that represents the change in concentration vs time for this reaction for AB, A2, and B2 where the concentration starts for [AB] at 12M and after some time appears to stop at 4M. AB is the red line and A2 and B2 is the black line. Concentration 4 Concentration 14+ 12 10 2+ 14+ 12 10 8- 2+ 14+ 12 10 1 2 3 4 5 Time 1 2 3 4 5 Time 1 2 3 4 Time 2 3 4 5 Time

. Suppose K=4.5103at a certain temperature for the reaction PCl5(g)PCl3(g)+Cl2(g)If it is found that the concentration of PCl5is twice the concentration of PCl3, what must be the concentration of Cl2under these conditions?

. In your own words, paraphrase Le Châtelier’s principle. Give an example (including a balanced chemical equation) of how each of the following changes can affect the position of equilibrium in favor of additional products for a system: the concentration of one of the reactants is increased: one of the products is selectively removed from the system: the reaction system is compressed to a smaller volume: the temperature is increased for an endothermic reaction: the temperature is decreased for an exothermic process.

Substances that poison a catalyst pose a major concern for many engineering designs, including those for catalytic converters. One design option is to add materials that react with potential poisons before they reach the catalyst. Among the commonly encountered catalyst poisons are silicon and phosphorus, which typically form phosphate or silicate ions in the oxidizing environment of an engine. Group 2 elements are added to the catalyst to react with these contaminants before they reach the working portion of the catalytic converter. If estimates show that a catalytic converter will be exposed to 625 g of silicon during its lifetime, what mass of beryllium would need to be included in the design?

An equilibrium involving the carbonate and bicarbonate ions exists in natural waters: HCO5_(aq) «=* H+(aq) + COf-(aq) Assuming that the reactions in both directions are elementary' processes: Write rate expressions for the forward and reverse reactions. Write an expression for the equilibrium constant based on the rates of the forward and reverse reactions.

Consider the reaction N2O4(g)2NO2(g). Draw a graph illustrating the changes of concentrations of N2O4 and NO2 as equilibrium is approached. Describe how the rates of the forward and reverse reactions change as the mixture approaches dynamic equilibrium. Why is this called a dynamic equilibrium?

. In general terms. what does the equilibrium constant for a reaction represent? What is the algebraic form of the equilibrium constant for a typical reaction? What do square brackets indicate when we write an equilibrium constant?

. Explain what it means that a reaction has reached a state of chemical equilibrium. Explain why equilibrium is a dynamic state: Does a reaction really “stop” when the system reaches a state of equilibrium? Explain why, once a chemical system has reached equilibrium, the concentrations of all reactants remain constant with time. Why does this constancy of concentration not contradict our picture of equilibrium as being dynamic? What happens to the rates of the forward and reverse reactions as a system proceeds to equilibrium from a starting point where only reactants are present?

The following series of diagrams represent the reaction XY followed over a period of time. The X molecules are red and the Y molecules are green. At the end of the time period depicted, has the reaction system reached equilibrium? Justify your answer with a one-sentence explanation.

Because carbonic acid undergoes a second ionization, the student in Exercise 12.39 is concerned that the hydrogen ion concentration she calculated is not correct. She looks up the equilibrium constant for the reaction HCO,-(aq) «=* H+(aq) + COf'(aq) Upon finding that the equilibrium constant for this reaction is 4.8 X 10“H, she decides that her answer in Exercise 12.39 is correct. Explain her reasoning. A student is simulating the carbonic acid—hydrogen carbonate equilibrium in a lake: H,CO,(aq) 5=6 H+(aq) + HCO,'(aq) K = 4.4 X 10'7She starts with 0.1000 A1 carbonic acid. W hat are the concentrations of all species at equilibrium?