prequizzes and answer keys

[Zellmer, Robert]

The answer keys to the prequizzes as well as blank prequizzes are posted to my class website ("Quizzes" link).



If you didn't take the pre-quiz, I would suggest you take it in the allotted time and then grade yourself.   This will

help you determine what you might not remember.  Remember as well, the prequiz does not cover everything

you need to remember from 1210, just some of the things you need to know right away.



I took a look at some of the quizzes and have a few comments below.  The TAs will grade them and we will put the

grades in Carmen so you'll have some idea of how you did.  They won't leave extensive comments since I've posted

the worked out solutions.



While some people had trouble with the other questions, the questions below are the ones I saw many people

having trouble with.



One thing I noticed is people didn't use dimensions analysis or didn't use it effectively for question #1.  You should

have been able it in one step.  The more steps you take to do a problem the more chances there are to make

mistakes.



I also noticed quite a few people had trouble with shapes and polarity of molecules.  You need to be able to tell

pretty quickly if a substance is ionic, molecular, metallic or covalent network.  If it's molecular you need to quickly

determine it's shape and polarity.  This is important in order for you determine attractive forces.  There's a link at

my "Notes" link which is about the four different types of solids and the attractive forces between the particles,

Types of Solids and Their Properties<https://www.asc.ohio-state.edu/zellmer.1/chem1220/notes/Table_13-10_solids_no_lines.pdf>.  Some people did have correct shapes and whether the molecules were

polar or nonpolar but for the wrong reasons.  It's as important to not only get the right answer but the right

reasoning.  If you don't truly understand it and you got "lucky" on one question you might miss the next one

because you didn't really understand the concept.



Another problem I noticed is many people didn't do the enthalpy of reaction question (#2) properly and/or had

trouble with relating the sign of something like delta(H) to whether a process is exothermic or endothermic.

You need to remember how to determine enthalpies of rxn from Hess's law and enthalpies of formation.  Also,

remember, when the system loses energy to the surroundings that is a negative energy change so q, delta(H),

delta(E) are negative and the process is exothermic.  If energy is absorbed by the system the process is

endothermic and the sign of q or delta(H) is positive.



    delta(H) = -10 kJ/mol    the process is exothermic, energy is released and can

                                              be treated as a product.



    delta(H) = +10 kJ/mol    the process is endothermic, energy is absorbed and can

                                               be treated as a reactant.



Dr. Zellmer

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