Chemistry 2000, Fall 1996, Thermodynamics Practice Problem Solutions

1. This is a heat balance problem. Since there is no indication to the contrary, we must assume that no heat is either gained or lost by the system (wood+water).

   

   Note that the answer comes out in because we set up the problem using temperatures in these units.

2. This is another heat balance problem, this one involving latent heat.

   

3. From , we can calculate for the reaction.

   

   However (since the standard free energy of formation of an aqueous proton is zero) so that

   

4. For the process

   

   

   This is a very large so it agrees with the usual rule about the solubility of alkali metal salts.

5. At the boiling point, the liquid and gas are in equilibrium so, for the process , . (We can use instead of because we are considering a pure solvent and the normal boiling point is taken at 1atm of pressure, which is the standard gas pressure.) That being the case, .

   

   or, in degrees Celcius, .

6. The reaction involves the breaking of two C-Br bonds (one per bromomethane molecule) and of an F-F bond and the making of two C-F bonds and of a Br-Br bond. Therefore

   

7. From the equilibrium constant, we can calculate :

   

   Given and , we can calculate :

   

   At (323K),