Effective Homework Assistance The evaluationof homework assignments takes various forms in general chemistry, for example, they can be handed in and graded or handed in and noted or have answers posted, or have solutions to problems posted. It has become the fashion to publish solutions to problems in a "Student Guide" for purchase. Each technique has advantages and disadvantages. Disadvantages of posting answers include the fact that the students might know they are wrong but not why; publishing the worked problem leads students to examine the details, then say to themselves, "Oh, I get it; I can handle that now," although they cannot. Even though they are admonished to work through the problem, they do not do so, and as a consequence they do not master the problem. An alternative technique is in use at this institution and seems to be more effective than the ahave. A few days after the homework has been assigned, a list outlining the steps in working the problems is published; the detailed solutions are not given, the numbers are not plugged in and the crank turned; the answers are not given. (Although these are helpful, they seem only to separate the good from the very good.) An example of a problem from thermochemistry and the list of steps is given below. The Problem: One mole of an ideal gas a t 1.00 atm is allowed to expand at constant pressure from room temperature to 100 *C.Calculate q, w , AE and AH for this process. The Steps 1. Since constant-pressure conditions are present, we can say that the q we are interested in is q p = CpAT. We have already learned from the kinetic theory that Cp = 5R12. 2. Now we know AH = qp. 3. Now calculate w = PAV by calculating VI and V2 according to the relation V = nRTIP a t the lower and higher temperatures and substituting for w = P(V9 - VI). 4. Calculate AE = q - w. To be sure, there ia mare than one way to go about solving many problems, especially ones in thermodynamics with its internal consistency, but the very act of outlining how to solve a problem has the pedagogical attraction of allowing the instructor to emphasize the use of certain thought patterns and equations or to reinforce a particular point presented in lecture. Moreover, students here grudgingly admit that they learned more this way although they hate it; this itself should recommend the technique. David F. Dever Division of Math and National Science Macon College Macon. GA 31297
Volume 68
Number 3
March 1991
189
