Tuesday February 2, 2011

Today began with the usual Web Assign reading sheet review, the answers to chapter 17:3-5 on page 35 were presented and explained in class. It is interesting to note that, according to Mr. H, J. Willard was A. a snazzy dresser, B. a real hunk, C. a true scientist, and D. a great uncle of Mr. H's. Unfortunately, the lack of any "select all" option posed a real challenge to students; this particular student happened to choose option C.

After that attempt at humor, Mr. H went over the previous blog post. Very helpful with explaining the conce

pts of entropy. The plan for today was to explain Gibbs Free Energy (ΔG), finish lab TC10 Reaction 2, and go over the Chapter 9 Quiz. Basically, ΔG is to be used to determine whether or not a reaction is spontaneous, non-spontaneous, or borderline (neither spontaneous nor non-spontaneous, the reaction can occur in either direction). The formula for finding Gibbs Free Energy is ΔG=ΔH-T*ΔS, where both ΔH and ΔS are in kJ and the temperature is in Kelvins. If ΔG was negative the reaction is spontaneous, if ΔG is positive the reaction is non-spontaneous, if ΔG was zero then the reaction is borderline. After that q

uick lesson, we turned to page 21 to practice using this formula.

Problem number 2 was a review of how ΔH and ΔS related to the spontaneity of the reaction. If both are positive the reaction is spontaneous at higher temperatures, if both are negative the reaction is spontaneous at lower temperatures. Moving on, it is important to always check that the units are the same before calculating ΔG. That is, T should be in Kelvins and ΔS should be converted into kJ.

On problem 6. c., although ΔG technically is a negative value, the reaction is classified as borderline. One's reasoning will vary from person to person, but in this case the ΔG value is so close to zero that the reaction would be classified as a borderline example regardless.

Next, we preformed Lab TC10 Reaction 2. Not all to different from the previous day's lab portion, for the most part the processes were identical. Since the data has been acquired, the conclusion/discussion will be done in class. After that little bit of fun, the Chapter 9 Quizzes were handed back to the students. Due to a grade calculation error, the multiple choice portion was graded out of 26 points instead of 22 points plus a 4 point written portion. Thankfully this error was fixed using some common sense and a rather fat Sharpie pen.

As for homework, the deadline for the Web Assign has been pushed back due to the snow day. Similarly, Delicious Bookmark assignments are due the next class day. That's all for now, enjoy a day without school!