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DP Study Guide to Chapter 18

DP Study Guide to Chapter 18 - DPs Study Guide to Chapter...

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DPs Study Guide to Chapter 18 Electrochemistry is DP’s most favorite subject. Unfortunately it has a bad reputation for being “hard” and most instructors skip it. If you have never studied electrochemistry, that’s great, a lot can be said about a virgin mind. Overview: We will start out with oxidation-reduction reactions. Then DP will break into some of his own explanations, then we will figure out how to make the electrons go up a wire. We will then study, batteries, electrical measurement of solution concentrations, equilibrium constants can be determined electrically. Section 18.1&2 Oxidation Reduction Reactions: First students ask: With reactions coming out of our ears, how do we ID the oxidation reduction ones? Answer: Look for a change in oxidation number for two of the atoms in the reaction mixture. This was a Chem 1 thing. If the oxidation number changes then it is an Rd/Ox reaction. How to balance and oxidation-reduction reaction? Hill lists ways that are almost the same. I just boil it down to one. 1) After identifying what is oxidized and reduced, divide the reaction in to two half-reactions 2) Balance all of the atoms but oxygen and hydrogen 2) Balance the oxygen with H 2 O 4) Balance the hydrogen with H + 5) Balance the charge with electrons, just so the total charge on both sides is the same. 6) Add the two reactions such that the electrons cancel (sometimes this mean multiplying the half reactions by a constant before adding. There is one other case: If the reaction happens in a basic solution take the sum from #6 and add hydroxide to both sides, to neutralize the hydrogen ion. Warning: You must follow the above order, otherwise it does not work! Work some problems: 26, 28, 29, 30 DP’s Interlude: Holy Rigatoni. Volta did not invent his “pile” so quickly. Why should an electron what to leave one compound and go to another? Same reason any thing happens: Energy and Opportunity. Electrochemistry is just another example of thermodyanamics To talk about energy we first have to explain what a volt is. If they did a good job for you in physics then this will be review. I always try to error to the side of caution. Ever seen an electron? Nope, me neither. Let’s get another example that we can put some visualization to: Gravity. Potential energy: mass X acceleration X height or mgh. This is good because it give you the relationship between location, ie where something is and its energy. Note that the bowling ball does not have to roll off the table and onto your toe to have energy. It has energy just because it is on the table.
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There is also a propensity for something to loose its potential energy, but you have to give it the opportunity, shove. Bowling balls move because the are placed in a gravitational field. How do you get a gravitational field in the first place? You separate very large masses measured in kg, developing a field of strength g, (the acceleration due to gravity) and place a bowling ball in the field, which will experience a force, mg. If you move the ball against the field, you will have to put in work, raising the potential.
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