Question

In Questions 6.1-6.4, you will be presented with four samples of student work related to problems in thermodynamics and energy transfer. In each case, your task is to determine if the student's conclusion is true or false. If you determine their conclusion to be "false," you must then point out the inaccurate parts of their statement and/or suggest a more accurate version. If you determine their conclusion to be "true," your work is done :) Question 6.1: Consider the hypothetical reaction XY2(g) -->X(s) + Y2(g) with AHrxn = -325 kJ/mol XY2. Can you predict whether this reaction favors the products or the reactants? Student Answer: The negative reaction enthalpy suggests an exothermic reaction. Because the products are more stable than the reactants, the products are favored. Question 6.2: Consider the hypothetical reaction XY2(g) --> X(s) + Y2(g) with AHrxn = -325 kJ/mol XY2. Was energy released or consumed when the X-Y bond was broken? Student Answer: The negative reaction enthalpy suggests an exothermic reaction, or one that releases energy. That energy must have been stored in the X-Y bond.

Answer 1

6.1 True

6.2 False. The negative reaction enthalpy implies an exothermic reaction i.e. it releases energy. The source of this released energy is the breaking of X-Y bond. So,energy released when X-Y bond breaks.

6.3 True

6.4 False. Positive $\triangle G^{\circ}$ value implies the reverse reaction is favoured. It will happen if we start the reaction with solid X and gaseous Y2.