Chemistry 2720, Fall 96, Assignment 1

Due: September 24

All questions are equally weighted. Most questions will require data not provided here. Sources for thermodynamics data include your textbook (esp. the Appendix starting on p 746 and the table of properties of water on p 33) and the course web site (http://people.uleth.ca/~roussel/C2720).

1. Calculate the work done when a gas expands from a volume of 1L to 10L against a constant external pressure of 1atm. (Hint and caution: The answer should be in SI units.)
2. An electric kettle has a 1500W heating element. It is filled with 1.5L of water at C. Assume that the kettle itself has a negligible heat capacity and that no heat is lost from the water during the heating process. How long does it take the kettle to bring the water to a boil?
3. Lead melts at C with a latent heat of fusion of 25J/g. The specific heat capacity of lead is 0.127JK g . Small spheres of uniform size are frequently made by dropping molten metal into water. A surface tension effect causes the metal to form almost perfect spheres and the water cools the metal very rapidly, causing it to solidify. Suppose that lead spheres each weighing 0.5g are being made by this process in a 1kg bucket of water. The spheres are removed quickly and their mean temperature on removal is found to be C. Assume that little heat is lost from the water to its environment and that negligible evaporation takes place. For safety reasons, it is desired to keep the water temperature below C at all times. If the water starts out at C, how many individual lead spheres can be made before the water must be changed?
4. In mammals, 1g of carbohydrates produces a maximum of 4.0kcal of useful work. A calorie is 4.184J. A shipment consisting of 24 boxes each weighing 10kg arrives at your office which you must lift to a shelf 1.5m off the ground. From your elementary physics, you recall that the work done on a mass m in raising it to a height h is mgh, where is the acceleration due to gravity. Instead of doing the job right away, you decide to procrastinate by solving a thermodynamics problem first: How much spaghetti (almost a pure carbohydrate) should you eat after carrying out this task to compensate for the work you will have done and avoid losing weight?
5. 1. Compute the standard enthalpy of combustion of acetylene to carbon dioxide and liquid water.
   2. Compute the standard change in internal energy during the combustion of acetylene. Treat all gases as ideal.

Volume conversion factors