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CHEMISTRY TEST REVIEW 4

CHEMISTRY TEST REVIEW 4 - Chemistry 1212/04 Review for Test...

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Chemistry 1212/04 Review for Test 4. Byason 1 of 23 17.58 Equilibrium position refers to the specific concentrations or pressures of reactants and products that exist at equilibrium, whereas equilibrium constant refers to the overall ratio of equilibrium concentrations and not to specific concentrations. Reactant concentration changes cause changes in the specific equilibrium concentrations of reactants and products (equilibrium position), but not in the equilibrium constant. 17.59 A positive H rxn indicates that the reaction is endothermic, and that heat is consumed in the reaction: NH 4 Cl( s ) + heat NH 3 ( g ) + HCl( g ) a) The addition of heat causes the reaction to proceed to the right to counterbalance the effect of the added heat. Therefore, more products form at a higher temperature and container (B) best represents the mixture. b) When heat is removed, the reaction shifts to the left to offset that disturbance. Therefore, NH 3 and HCl molecules combine to form more reactant and container (A) best represents the mixture. 17.60 Equilibrium component concentration values may change but the mass action expression of these concentrations is a constant as long as temperature remains constant. Changes in component amounts, pressures (volumes), or addition of a catalyst will not change the value of the equilibrium constant. 17.61 a) Rate f = k f [Reactants] x . An increase in reactant concentration shifts the equilibrium to the right by increasing the initial forward rate. Since K eq = k f / k r and k f and k r are not changed by changes in concentration, K eq remains constant. b) A decrease in volume causes an increase in concentrations of gases. The reaction rate for the formation of fewer moles of gases is increased to a greater extent. Again, the k f and k r values are unchanged. c) An increase in temperature increases k r to a greater extent for an exothermic reaction and thus lowers the K eq 17.63 a) Equilibrium position shifts toward products . Adding a reactant (CO) causes production of more products. b) Equilibrium position shifts toward products . Removing a product (CO 2 ) causes production of more products. c) Equilibrium position does not shift . The amount of a solid reactant or product does not impact the equilibrium as long as there is some solid present. d) Equilibrium position shifts toward reactants . Product is added; dry ice is solid carbon dioxide that sublimes to carbon dioxide gas. At very low temperatures, CO 2 solid will not sublime, but since the reaction lists carbon dioxide as a gas, the assumption that sublimation takes place is reasonable 17.64 a) no change b) no change c) shifts toward the products d) shifts toward the reactants 17.65 An increase in container volume results in a decrease in pressure. Le Châtelier’s principle states that the equilibrium will shift in the direction that forms more moles of gas to offset the decrease in pressure.
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