9/16/13-9/20/13

This week in AP Chemistry, I continued to learn about stoichiometry. However, this week it became more complicated as limiting reactants, excess reactants, and yield were added into the mix. To help learn the concept of limiting reactants, I completed several worksheets, including Stoichiometry 6 & 7. I also viewed a lecture on limiting reactants. Limiting reactants are reactants that limit the amount of substance that is produced in a chemical reaction. To determine the limiting reactant, you calculate the amount of product produced by each reactant. Whichever reactant produces the least amount of product is the the limiting reactant.

An example of how to find the limiting reactant from the worksheet Stoichiometry 6. 153.5 g of carbon monoxide produces in 175.6 g of methanol. 24.50 g of hydrogen produces 194.0 g of methanol. Since carbon monoxide produces a lesser amount of methanol, it is the limiting reactant.  

I found this concept straightforward and easy to understand. The concept behind excess reactants is similar. When the limiting reactant is used up there is excess of the other reactant. This is the excess reactant. Initially, I did not fully understand how to determine the amount excess reactant. However, after searching online, I found this website which helped me to understand the how to calculate excess reactant. To help learn the concept of excess reactants, I completed the Reaction Particle Diagrams worksheet in class.

I found the concept of yield straightforward as well. There are two kinds of yield: theoretical yield and actual yield. Theoretical yield is the calculated maximum amount of product possible from a given amount of reactant. Actual yield is the measured amount of product experimentally produced from a given amount of reactant. Percentage yield can be determined by the following equation:

In order to understand the concept of yield, I had to complete the Stoichiometry 8 worksheet, which is comprised of problems in which one must calculate the percentage yield of reactions.

Additionally, this week I was introduced to the concept of empirical formulas. An empirical formula is a formula that represents the simplest ratio among the elements of a compound. (for example, the empirical formula of glucose, C6H12O6 is CH2O). Ionic compounds are always empirical formulas. Molecular formulas are sometimes empirical formulas. I was required to complete the Empirical Formulas 1 worksheet, in which I had to determine the empirical formula of compounds when given the mass composition of each compound.

I found in class this week that we completed many of the stoichiometry worksheets by having different groups writing the answers on whiteboards. While this is one way to learn the concepts, I found myself mindlessly copying down the answers. I think that I learn more effectively when there is a lecture quiz that offers guidance on the worksheet and I must complete most of the worksheet on my own.

With that being said, I feel as though I have a relatively strong understanding of all of these concepts. However, at the same time I think that some more practice would certainly not hurt. I will review the worksheets I did this week before the test this upcoming week.