Confidence Building Questions A closed container with N2O4 and NO2 gases in it, and it has been placed in the lab for many days. What would you consider the container and the gases to be? a. an open system b. a closed system c. not a system Answer b Discussion... Since it has been in the lab, the temperature of the system is the same as its environment. A closed container with N2O4 and NO2 gases in it, and it has been placed in the lab for many days. Is the system at an equilibrium state for the chemical reaction? N2O4 = 2 NO2 Answer yes Discussion... Only a few minute is required for the reaction to reach an equilibrium state. NO2 is a brown gas A closed container with N2O4 and NO2 gases in it, and it has just been placed in an ice/water bath. Is the system at an equilibrium state for the chemical reaction? N2O4 = 2 NO2 Answerno Discussion... Heat will be extracted from the container, and that cause the equilibrium to shift. At 0 deg C, the equilibrium is shifted to have lots of N2O4. If the equilibrium constant for the reaction equation HCOOH + CN- = HCN + HCOO- is 5E5, what is the equilibrium constant for the reaction equation HCN + HCOO- = HCOOH + CN-? Answer 1/5E5 = 2E-6 Discussion... Since the reaction equation is reversed, use the relationship Kreverse = 1/Kforward. If you reverse the reaction equation, take the reciprocal of the previous equilibrium constant. For reactions taking place in the gas phase, the equilibrium constant is normally expressed in terms of partial pressures of the reactants and products. If C represents the concentration, and other symbols of the ideal gas equation are used, which of the following is correct? (a) C = RT/(PV) (b) C = RT/P (c) C = RT/V (d) C = RT/(PM) (e) C = P/(RT) (f) C = PV/(RT). Answer e Discussion... By definition, C = n / V. Derive it from n R T = P V. If Kc represents the equilibrium constant in terms of concentration, and Kp represents that in terms of partial pressure, which of the following is correct? (a) Kc = Kp (b) Kc is proportional to Kp (c) Kc = 1/Kp (d) Kc is inversely proportional to Kp (e) Kc * Kp = RT Answer b Discussion... Statements (c), (d), and (e) may be true for special cases, but they are not generally true. In this list, Kc is proportional to Kp is true, but a more quantative relationship will be derived. For which of the following gas-phase reaction equations are the equilibrium constants unitless quantities? (a) 2 H2 + O2 = 2 H2O (b) 2 NO = N2 + O2 (c) COCl2 = CO + Cl2 (d) CO + H2O = CO2 + H2. (Give the letter(s) of your choice(s), e.g., ad).
Posted on: Sun, 14 Jul 2013 18:06:45 +0000
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