Honors Chemistry - Thermo Test

For each of the following problems, show all work. Use correct units and significant figures. No credit will be given for problems without work. For any questions on the test, be concise (make your answers complete but brief). Complete sentences are not required although complete thoughts are.

  1. Several years ago a company invented plastic ice cubes. These were colored plastic cubes with frozen water (or another substances) inside. That way, as the solid melted, it could cool your drink, but did not dilute it with extra water (from the melted ice). If plastic cubes containing 86.3 g of frozen stuff are placed into 150.0 g of water at 38.0oC and the temperature drops to 29.4oC, what is the heat of fusion of the stuff in the cubes. Assume the plastic does not effect the heat transfer in any way.
  2. Use bond energies to find the D H for the combustion of C3H8. Now calculate the D H for the same reaction using the thermo tables. Why are the values NOT the same? (For this calculation, assume that any water produced is in liquid form.)
  3. Use Hess' Law to calculate the heat of the following equation. Show all work including the reactions that you use, in the form that you use them.

    4.  2 C + 2 NO2 ---> 2 CO 2 + N 2

    You may use any or all of the following reactions:

     2 CO + O2 ---> 2 CO 2 ΔH = -164.7 kJ

     N2 + 2 O 2 ----> 2 NO 2 ΔH = -341.0 kJ

     2 C + O2 ----> 2 CO ΔH = -28.67 kJ

  4. Determine the D G for the unbalanced reaction HgSO4 + Al ® Al2(SO4)3 + Hg at 347oC. Be sure to balance the reaction BEFORE you do any calculations. What does the sign on D G mean? D H? D S?
  5. Bermuda is due East off of the Carolina coast, yet it has much milder winters. Why?
  6. Draw the graph of heat v. time for an endothermic reaction. Label the activation energy and the heat of reaction.
  7. A 34.6 g block of metal at 2.1oC is dropped into 100.0 g of water at 97.3oC. If the specific heat of the metal is 0.084 cal/goC, what will the final temperature of the water be?