This week, we learned more about stoichiometry, limited and excess reactants, reaction particle diagrams, yields, and empirical formulas. Stoichiometry is the mass and amount relationships between reactants and products in a chemical reaction. You start with the grams given, use molar mass of the given molecule to convert it to moles of the given molecule. Then you use a mole ration from the balanced equation to get moles of the unknown molecule. Using that, you use molar mass of the unknown molecule to convert it to mass of the given molecule and get grams calculated at the end. During a chemical reaction, if there are fixed amounts of reactants to work with, one of the reactants may be used up first. This prevents the production of more products. To do this in class, we used the example of assembling a race car and having a fixed set of parts to make one race car, and there was always a part that there wasn't enough of to make an entire race car, so that was the "limiting reactant". We also learned that the reactant with the smaller number of moles isn't always the limiting reactant. It all really depends on the ratios of the reactants, and the one with the smallest ratio is the limiting reactant.
We used reaction particle diagrams to show before and afters of reactions. Theoretical yield is what you're supposed to get, and it rarely gets 100%. Actual yield is what you get (lower than theoretical) and it's the measured amount or produced experimentally. The percentage yield formula is
(actual yield/theoretical yield)X100%.
An empirical formula is a formula that represents the simplest ratio among the elements of a compound. http://www.chem.tamu.edu/class/majors/tutorialnotefiles/empirical.htm (really explains the empirical formula).
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| Reaction particle diagrams |
I really understand the stoichiometry problems and finding the limited and excess reactants. I think that I need a little more practice with empirical formulas, but I understand the idea of them and what they mean.
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