10. What percentage of nitrogen contained in (NH4)2CO3 by mass? (A) 58.3% (B) 14.6% (C) 29.2% (D) 18.8% 【背面尚有試題】

17. Which of the following is true about a system at equilibrium? (A)The concentration(s) of the reactant(s) is equal to the concentration(s) of the product(s). (B) No new product molecules are formed. (C) The concentration(s) of reactant(s) is constant over time. (D)The rate of the reverse reaction is equal to the rate of the forward reaction and both rates are equal to zero.