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Maryknoll School CHEM ChemistrySuppEx_Solution_4B_E

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Unit 39 An introduction to chemical equilibrium Fill in the blanks 1 irreversible 2 reversible 3 dynamic 4 a) yellow; orange; Cr2O72–(aq); CrO42–(aq) b) orange; yellow; CrO42–(aq); Cr2O72� ... ��(aq) 5 a) forward b) backward True or false 6 T 7 F The composition of a system at equilibrium remains constant. Although the rates of the forward and backward reactions are the same, it does NOT mean that the concentrations of the reactants and the products are the same at equilibrium. 8 F Equilibrium can only be established in a closed system. 9 F The value of Kc for a reaction can be used to judge the extent of a reaction, but NOT the rate at which equilibrium is attained. 10 T If Qc > Kc, the system is not at equilibrium. Concentrations of the products must decrease and that of the reactants must increase until Qc = Kc. Thus, a net backward reaction must occur until equilibrium is reached. Multiple choice questions 11 C Option A — For a reaction system at equilibrium, the forward and backward reactions still continue all the time. Option D — The composition of a system at equilibrium remains constant. However, the amount of products may NOT be equal to the amount of reactants.2 12 D Rate of forward reaction 2SO3(g) 2SO2(g) + O2(g) Rate of backward reaction 2SO2(g) + O2(g) 2SO3(g) At start high zero As reaction proceeds (before equilibrium) decreasing increasing but rate of forward reaction > rate of backward reaction At equilibrium rate of forward reaction = rate of backward reaction GPSXBSESFBDUJPO 40 H 40 H 0 H CBDLXBSESFBDUJPO 40 H 0 H 40 H TZTUFNJT OPXBU FRVJMJCSJVN SBUFPG GPSXBSE SFBDUJPOSBUF PGCBDLXBSE SFBDUJPO UJNFUPSFBDI FRVJMJCSJVN 5JNF 3FBDUJPOSBUF 13 B Option B — After equilibrium has been established, the composition of the system remains constant. Thus, [H2(g)] remains constant. 14 C Option C — Equilibrium can be reached from either direction, starting with the substances on the left of the equation (i.e. H2(g) and I2(g)), or starting with the substances on the right (i.e. HI(g)). Thus, [HI(g)] in experiment A equals [HI(g)] in exp [Show More]

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