Hess' Law

The class started off today with Liebs showing us the experiment that failed yesterday. He was showing us how the process of sublimation could change to fusion. In order to do so he put frozen carbon dioxide, or dry ice, under "intense" amounts of pressure.

Once the dry ice melted under the water, it would pop under the pressure and send water everywhere, which was terrifying to some of the people in our class... so this is is the same thing, but without the "pop".



Moving onto the lecture today, we spent the rest of class discussing something called Hess' Law. Hess' Law basically says that you can use multiple ways to find Hess' Law, and it will still work, as long as you come to same, correct conclusion.

"If you ski down a hill, it doesn't matter the path you take, you're still going to get to the bottom. As long as you don't hit a tree."

Basically you are given a formula, and you must add and subtract a series of other equations to match it, and then do the same process to series' delta H's in order to find the original missing delta H. To change the equations you can do one of two things: you can flip the formulas around or multiply their coefficients by a number. When adding the equations, if they are on the opposite side of the arrow and the same element/compound they cancel. If they are on the same side then they combine.

An example:

Limiting Reactants

Friday, in Liebs' class, we did four major things.

First we finished our labs by decanting the water of our beakers, and massing our silver.  This is largely uneventful, but necessary to complete the lab. The result probably looked something like this:

Which, let's be honest, is a little gross.

Post-Lab question #6 requires some outside knowledge.

It asks for the current market price is silver, which according to the most recent statistic on Wikipedia is on average $24.38 per troy ounce of silver.

The post lab gives the conversion 1 Troy ounce= 31.0 grams, so convert your mass to troy ounces, then multiply the times $24.38.

Next Liebs answered questions on the Super Mole Fun worksheet. He has the first three problems worked out here, just scroll down to the super mole fun pdf. (Public Data File)

After that we took our quiz, which covers what Tom talks about in his lovely post below. It was mostly converting grams to moles to grams again, in order to determine how much of a product would be produced, or reactant was need.

Next, were our notes on limiting reactants.

For some reason my computer hates me, and refuses to put the embeded slideshow of the notes in but the link may be found here starting on Slide 8.

A limiting reactant is the reactant that produces the least amount of product.  There are two ways to do this.  The first is to find to choose one of the actual amounts of  reactant used and determine how much of the other reactant it would need.  Then compare the number you found to the actual number used, and if it's less than what was used, then that is the limiting reactant. However, Liebs doesn't reccomend this method, instead he suggests the second one: determine in two equations how much of the product each reactant produces, and compare.  This method is better because it is clearer, and most labs/worksheets will also ask you how much of the product each reactant produces anyways.

Liebs ended class by tell him two things had made his day: one, was someone couldn't figure out how to turn off a solar-powered calculator. The second was this beauty right here....



"baby monkey, baby monkey..."

Next scribe is..... Amar! Congrats bud.