Part III: Examining Changes in Terms of Energy in VS .NET

Making European Article Number 13 in VS .NET Part III: Examining Changes in Terms of Energy

Consider the following reaction: N2(g) + O2(g) 2NO(g) At equilibrium, you measure the following partial pressures: P(N2) = 476 10 2 atm, P(O2) = 982 10 3 atm, and P(NO) = 263 10 7 atm a What is the Keq for this reaction b If you measured P(O2) = 374 10 2 atm, and other partial pressures remained unchanged, what is the reaction quotient for the reaction In which direction would the reaction proceed

You perform the following reaction: 2A + 2B 3C + D After waiting three hours, you measure the following concentrations: [A] = 273 mM, [B] = 347 mM, [C] = 0443M, and [D] = 789 mM a What is the reaction quotient for the system b If the Keq for this reaction is 185 102, has the reaction completed

Consider the reaction A + B 2C The free energy change for this reaction is 258 kJ mol 1, and the enthalpy change for the same reaction is 123 kJ mol 1 a At 273K, what is the entropy change for the reaction What drives the reaction forward favorable enthalpy change, favorable entropy change, or both b What is the expression for Keq for the reaction, and what is its value c If a reaction mixture at equilibrium contains 0744M reactant A and 117M product C, what is the concentration of reactant B

After a chemical system has reached equilibrium, that equilibrium can be disrupted, or perturbed Think of systems at equilibrium as people who have finally found their easy chair at the end of a long day You may rouse them to take out the trash, but they ll return to the easy chair at the first opportunity This concept is more or less the idea behind Le Chatelier s Principle: The equilibrium of a perturbed system shifts in the direction that minimizes the perturbation Perturbations include changes in concentration, pressure, and temperature Concentration: If a system is at equilibrium, Q = Keq Adding or removing reactant or product disrupts the equilibrium such that Q < Keq or Q > Keq The equilibrium reasserts itself in response If reactant is added or product is removed, reactant converts into product If product is added or reactant is removed, product converts into reactant Either way, chemistry occurs until Q = Keq once more The equilibrium shifts to oppose the perturbation Pressure: Reactions that include gases as reactants and/or products are particularly sensitive to pressure perturbation If pressure is suddenly increased, equilibrium shifts toward the side of the reaction that contains fewer moles of gas, thereby decreasing pressure If pressure is suddenly decreased, equilibrium shifts toward the side of the reaction that contains more moles of gas, thereby increasing pressure Consider the following reaction: N2(g) + 3H2(g) 2NH3(g) A given amount of mass on the reactant side of the equation (as N2 and H2) corresponds to double the moles of gas as the same mass on the product side (as NH3) Imagine that the system is at equilibrium at a low pressure Now imagine that the pressure suddenly increases, perturbing that equilibrium Reactant (N2 and H2) converts to product (NH3) so the total moles of gas decrease, thereby lowering the pressure If the system suddenly shifts to lower pressure, NH3 converts to N2 and H2, so the total moles of gas increase, thereby raising the pressure The equilibrium shifts to oppose the perturbation Temperature: Reactions that absorb or give off heat (that is, most reactions) can be perturbed from equilibrium by changes in temperature The easiest way to understands this behavior is to explicitly include heat as a reactant or product in the reaction equation: A + B C + heat Imagine that this reaction is at equilibrium Now imagine that the temperature suddenly increases Product C absorbs heat, converting to reactants A and B Because the heat product has been decreased, the temperature of the system decreases If the temperature suddenly shifts down from equilibrium, reactants A and B convert to product C, releasing heat The released heat increases the temperature of the system The equilibrium shifts to oppose the perturbation