Chemistry 2000, Fall 96, Test 3 Solutions

1. The equilibrium is

   

   The activities of the nickel and sulfide ions are related by . Therefore

   

2. The equilibrium is

   

   Thus we have . However, by stoichiometry, . We can find the activity of hydroxide from the pH:

   

3. This is a heat balance problem. The heat given off by the iron is balanced by the heat absorbed to melt the ice.

   

   . so the initial temperature of the iron was or 309K.

4. For this reaction

   

   However, since the free energies of formation of boron and of hydrogen are both zero. Therefore

   

5. 1. This is calculated from the free energies of formations of the reactants and products:

      

   2. To calculate at any temperature other than 298K, we need and .

      

6. To decide whether the reaction is spontaneous, we need to calculate .

   

   Since , the reaction is not spontaneous.