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Analytical Chemistry
Learn the toughest concepts covered in your Analytical Chemistry class with step-by-step video tutorials and practice problems.
Chemical Equilibrium
Le Chatelier's Principle
Le Chatelier's Principle discusses the shifting pattern of a chemical reaction in order to maintain an equilibrium state.
Chemical Thermodynamics
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Le Chatelier's Principle
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So the chandeliers principle states that if we have a chemical reaction at equilibrium and we do something to disturb that equilibrium, the reaction will adjust by shifting either in the four directions or reverse direction in order to minimize any changes so that it stays at equilibrium. Now there's a lot of different things that we could do to try to disrupt this equilibrium. So we'll go through each one of the scenarios and see what caught, what effect does that have on the chemical reaction itself. So first we can talk about reactant and products. So we're gonna say here, if you are adding react ints or removing products, that means that our reaction is going to shift to the right, which means the four directions. So we'd be shifting this way. That's because if you're adding reactant so you need to get rid of the excess reactant you've just added. And the only way to do that is to move in the four direction to get rid of it in the opposite way. If you remove any products, you need to remake the products that you've just lost, how would you do that again? You would move in the four direction or to the right to replenish and remake those products. So for shifting to the right, that means that wherever we're moving will be increasing in amount. So here we expect our products to be increasing to make up for what we lost or we'd and we'd expect here are reactions to be decreasing just in case we added react ints. So just remember adding reactant or removing products, we shift to the right now. If we do the opposite we should expect the opposite result. So if I remove my reactant I need to remake the reactions I've just lost. How would I do that? My reaction would have to move in the reverse direction or to the left to remake the reactant I've just lost. If I add additional products, how do I get rid of those additional products that I've added? Again, I'd move in the reverse direction to get rid of them. So again under this situation we're gonna shift to the left or the reverse direction again, wherever we're heading will be increasing an amount. So hear my reactions will be increasing in amount as a result and my products would be decreasing an amount. So remember adding or removing products will have some type of effect in terms of my reaction. Remember these two principles whether you're adding or removing reactions or products determines which direction will shift. So come back, click on the next video and see what happens when we adjust the pressure or volume
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Le Chatelier's Principle
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Now here we're going to adjust the pressure and volume and see what changes it has on the chemical reaction. So here we're gonna say if we're decreasing pressure, that's the same thing is increasing volume because they're inversely proportional, they're basically opposites of one another. So for decreasing pressure or increasing volume, the re actual shift to the side with more moles of gas. So if we take a look here, we can see that we have two moles of gas, one mole of solid. So overall, here we have two moles of gas, and on this side we have three moles of gas, one mole of solid. So overall we have three moles of gas. So again, if we're decreasing pressure or increasing volume, we're gonna shift to the side with more moles of gas. So in this example we shift in the forward direction, remember wherever we're shifting will be increasing in amount. So we expect our products to be increasing and if the product side is increasing, that means that my reacting side is decreasing. Then if we do the opposite here we're increasing the pressure, which means that we're decreasing the volume. So the reaction would shift to the side with less moles of gas. Again, we still have two moles of gas overall here, three moles of gas here, we're going to shift to the side with less moles of gas. So the side that has two moles of gas in this example, wherever we're shifting will be increasing an amount and if that's increasing amount, that means the other side is decreasing an amount. So remember if we're affecting pressure and volume, we're gonna look and see what sides have either more moles of gas or less moles of gas. If both sides have an equal number of gas molecules, then no shift will occur, because again, we're always looking to see do we shift to the side with more moles or less moles of gas? And if both sides are equal, there's no direction we can shift. Not that we've seen this one will move on to the effects of temperature in terms of shifting a chemical reaction. So click onto the next video and see how temperature plays a role in the chandeliers principle.
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Le Chatelier's Principle
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now whenever we're dealing with temperature and how it affects the rattlers principle we first have to determine is our reaction, eggs are thermic or endo thermic. So in X. A thermic reaction has a negative delta H. Or envelop here, heat would be a product because in an exotic thermic process we release heat. So heat will be a product if delta H. Is positive. That means we're dealing with an indo thermic process. So that means heat will be reactant in an endo thermic process. We absorb heat. So heat will be a reactant. Now if we're increasing the temperature, if you're increasing the temperature the reaction will shift away from heat. Yeah and again you need to determine if it's an XR thermic or endo thermic process. So you can see what side heat is on. In this example we're looking at an endo thermic process because heat is a reactant, we're increasing temperature. So we're gonna shift away from heat. So we move to the right side because that will be away from the heat source wherever we're shifting to will be increasing amount. And then and then this side would have to be decreasing an amount. So again you can't determine which way reaction will shift until you first figure out is an endo thermic or exhaust thermic. Now here for decreasing the temperature reaction will shift towards heat. So heat here is still on the reacting side. So this is still an endo thermic process. So here we would shift this way towards my heat. So that would mean that this year would be increasing and this side here would have to be decreasing. So whether temperature is increasing or decreasing is not enough information you first have to determine. Is it eggs a thermic or endo thermic? Place the heat on the appropriate side, whether it's reactant for endo thermic or whether it's a product for exa thermic. Once you determine the side the heat is on, then you can look and see okay, what effect will increasing or decreasing the temperature have in terms of shifting this chemical reaction based on the chandeliers principle. So a few factors down. We'll go on to inert gasses in the next video. So click on the next video and see what happens when we're dealing with inert gasses, chandeliers principle.
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concept
Le Chatelier's Principle
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So now when we talk about the addition of an inert gas, we're really referring to a noble gas being added to our mixture. And remember our noble gasses are just the elements from Group eight A on the periodic table. Now, here we're gonna say if you're adding a noble gas under constant volume, we're gonna say there will be no shift in the equilibrium position. So our reaction will not shift in the four direction or the reverse direction. So we'd say here that this would result in no change. And also here, no change If you added under constant pressure though, when we added under constant pressure, the reaction will shift to side with more moles of gas. So here adding it under constant pressure here we have two moles of gasses which we figured out earlier Here we have three moles of gasses. So we'd shift aside with more modes of gasses, so we shift that way wherever we're shifting that be increasing and over here this would be decreasing. Now when they're talking about the addition of inert gas by default, they're usually talking about adding it under constant volume. So you would expect no shift in the equilibrium position. If they want to be more specific, they would have to tell you under constant pressure so that you would know to do it under the second situation. But for the most part, when they say the addition of a nerve gas or noble gas, that means that no change in the equilibrium position will occur. Now, finally, we look at liquids, solids and catalysts. So we're gonna say here, they're addition, there will be no shift in the equilibrium position. That's because when it comes to liquids and solids, they're not included in terms of equilibrium. Remember any time we do an equilibrium expression, we always make sure to ignore solids and liquids. That's because they don't influence equilibrium amounts within our calculations. And then a catalyst, a catalyst only helps to speed up the chemical reaction by lowering the activation energy rates, deals with chemical kinetics. But when we're talking about shifting that's covering chemical thermodynamics, those are two separate ideas. So catalyst only affects rate, It doesn't affect position. So the addition of any of these three we're gonna say will cause no change. So the addition or removal of them causes no change. Mhm. So these are all the factors that we can manipulate in order to cause our chemical reaction to shift in the four direction for the production of additional products or in the reverse direction for the production of additional reactant. So keep in mind each one of these changes and the different guidelines that are associated with each
Under equilibrium conditions, the addition or removal of a liquid, solid or catalyst will cause no shift in the reaction's position.
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example
Le Chatelier's Principle
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So here it says the following data was collected for the following reaction at Equilibrium. Hayward told that 55°C, our equilibrium constant K is 4.7 times 10 to the -7. And at 100°C, K now becomes 1.9 times 10 to the negative. To where asked which of the following statements is true. Alright, so remember, the only real factor that can affect my equilibrium constant is temperature. Here we see that our temperature is increasing. So temperature is increasing. Now we have rules in terms of the Chancellor's principle that discuss what happens when we affect temperature. And according to the Chancellor's principle, it says that when we increase temperature, we're gonna shift away from heat. Okay, so that's what the increasing temperature is telling us. Now, we have to figure out what side is heat on. How can we determine which side heat is on? We can determine that by figuring out which way does my chemical reaction shift. If we take a look at 55 degrees Celsius, your equilibrium constant is 4.7 times 10 to the negative seven. When we increase the temperature it actually increases. Now it's 1.9 times 10 to the negative two. So we're gonna say here, if you're increasing your equilibrium constant. K. That gives us a clear indication of what of which direction our reaction is shifting. So think about it. K equals products. Overreacting. The only way for K to increase is from my product amount to go up to increase and my reacting amount to decrease. So when K is increasing, that means products are increasing and react ints. Mhm are decreasing. Okay, so think about it. How can that happen in terms of shifting in a chemical reaction? Well, if my products are increasing, that must mean my reaction is shifting towards them. So we must be heading in the four directions so that my products are increasing and so that this side here is decreasing. So looking at K if it's increasing or decreasing gives me the direction involved. We figured out that we're heading in the forward direction, going back to temperature, we would be shifting away from heat. So for shifting in the four direction, that must mean that heat is a reactant, it's on the reacting side. So we normally shift away from it with the increase in temperature. So if heat is a reactant, that must be my reaction is endo thermic a positive delta H value here. So A. Is out. The entropy change for DELTA H is equal to zero. So if DELTA H is equal to zero, that means that we're thermal neutral. If we're thermal neutral, that would mean that increasing the temperature or decreasing the temperature would cause no change in my equilibrium constant. So K would stay the same exact value. If we were indeed thermal neutral. Since K is changing when I change temperature, we know that DELTA H cannot be equal to zero. And then finally we did have enough information. We figured out that the reaction is endo thermic. So again, the two things that we look at is we look at the change in temperature to determine um what we're following in terms of the Chancellor's principle and then we look at K. Is it increasing or decreasing? This helps us to determine which direction my chemical reaction will shift. Then apply Chancellor's principle with temperature to determine what side the heat is on now that we've seen this. Um We'll go on to example two in terms of the settlers principle. Um Go ahead and try to see if you can get the answer. If you get stuck. Don't worry. Just come back to the next video and see how I approach example too.
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example
Le Chatelier's Principle
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mhm. In which of these gas phase equilibrium is the yield of products increased by increasing the total pressure on the reaction mixture. Alright, so here they're saying that we're increasing the pressure. Remember increasing the pressure the same thing as decreasing volume. So we're gonna shift to the side with less moles of gas. We want to increase the amount of products made, so we want to shift towards the products. So, if we take a look here in the first one, we have two moles of gas is as reactant and we have two moles of gasses as products, because both sides have the same number of moles increasing or decreasing the pressure will cause no shift because we can't go to the side with more or less moles of gas. Next this one has 3 moles of gas. This side only has two moles of gas. So we shifted the side with less moles of gas since the pressure is increasing, so we would shift towards the product side. So the product would be increasing. So this is an answer. Next. We have two moles of gas here for react ints and we have three total moles of gas here as products. We shift this way towards the side with less moles of gas. So in this case reactant would actually be increasing not products here we have one mole of gas and here we have two moles of gas. So, like an option, C would shift to the side with less moles of gas, so reacting would be increasing again. Then here we have two moles of gas here we have three moles of gas. So again we shifted the side with more more or less moles of gas, so we'll be shifting towards the reacting side so the reactions again would be increasing. So the only option here where the products are being increased because we're shifting towards them is option being. Remember, increasing the total pressure is the same thing as decreasing the total volume. We would shift to the side with less moles of gas.
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Problem
The reaction 2 NaHCO3 (s) ⇌ Na2CO3 (s) + H2O (g) + CO2 (g) is endothermic. What would you do in order to maximize the yield of Na2CO3 (s)?
A
Lower the temperature and increase the volume of the container.
B
Raise the temperature and add CO2(g) and H2O(g).
C
Lower the temperature and decrease the volume of the container.
D
Add CO2(g) and H2O(g) and increase the volume of the container.
E
Increase the volume of the container and raise the temperature.
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