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Great Thanks to Tina Nye (A-5; 05-06) for much work on graphics: making a rough idea reality! Chemical equilibrium A system in equilibrium is like our ants up there! As long as the ants work at the same speed, the piles of sand remain in equilibrium. Neither gets bigger or smaller (It is important to note however that the piles are not the same size!). The work that each ant does exactly offsets what the other is doing. Products are being stacked up and the same rate that they are being taken away. Reactants are being stacked up at exactly the same rate that they are being taken away. If this were a chemical reaction, reactants would be colliding to make product at the same rate that products would be colliding with each other to make fresh reactant again! The reaction never really stops, but the forward reaction and reverse reaction proceed and the same rate, so we don't see a change in the size of the piles! Nifty Huh!!!!? Chemical equilibrium is reached when the rates for the forward and reverse chemical reactions are equal for a chemical system. Or you could say when products are being made as fast as they are breaking down to form reactants again. The concentrations of products and reactants are generally NOT EQUAL.
Keq = [products]/[reactants]. Its a ratio : ) So Keq > 1 favors products, Keq < 1 favor reactants. For a general equation like: wA + xB <===> yC + zD Remember, the square brackets mean concentration, in molarity, if it is given in some other unit you must calculate molarity. Coefficients in the chemical equation become exponents in the Keq expression. Leave out any solids or pure liquids since they have undefined molarities ; ). Keq= If you spend time with the following notes, you'll master this topic in no time. Predicting final concentrations and cheating while were doing it.
Le Chatelier's Principle
Le Chatelier's Principle notes. Ionization of Acids and Bases: Ka & KbStrong acids or strong bases always disassociate (ionize) 100%, we really aren't going see much of them in this unit. Weak acids and weak bases on the other hand like to stay together as molecules, they don't disassociate very much. The measure of how "strong" an acid is is given by Ka. The measure of how "strong" a base is is given by Kb. A high Ka means that you get more ionization so produce more H3O+ (hydronium) in a solution with water. More hydronium means you have a "stronger" acid. Ka = [products]/[reactants]
Sample Problem
1) Chemical
Equation for ionization of hypochlorous acid: HClO <---> H+ +
ClO-
The Solubility Product: Ksp Ksp comes from Keq, only this time our reactants are solid so they get left out. That is because for a solid concentration is meaningless. I mean the solid is 100% solid but there is no solvent so you are sort of dividing by 0 to try to get concentration. Ksp= [Products] Steps in solving problems
A thorough text heavy set of notes. Predicting Precipitation Predicting whether precipitation occurs boils down to one question. Is my ION PRODUCT
(Qip) greater than the KNOWN SOLUBILITY PRODUCT (KSP)?
Sample problem The final concentration of
CaCl2 in a solution is 1.5 x10-5 M and the final concentration of NaF in a solution
AFTER mixing is 2.2
x10-2 M Will precipitation occur?
Step 1: Write a balanced dissolution reaction.
Looks like Qip is greater than Ksp!!! |