Intro to Chemical Equilibrium - Video Tutorials & Practice Problems
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Intro to Chemical Equilibrium
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Hey, everyone. So in this set of videos, we're gonna take a look at chemical equilibrium. Now what we're going to say first is that most chemical reactions never go to what we call completion. This means that not all the reactants are converted into products, Instead, we reach what's called a chemical equilibrium. Now we're gonna say chemical equilibrium is the dynamic process where the rate of the forward and reverse reactions are equal to one another. Now what kind of effect will this have? Well before we get to that, we're also going to say that a dynamic process is means that the reaction does not simply stop. That keeps going in both directions. So when we refer to chemical equilibrium we're going to say these reactions are reversible. And because they're reversible they're going to use double arrows. We're gonna have 1 arrow that moves forward, and we're gonna have another arrow that moves in the reverse direction. Now coming back to this idea of forward and reverse reactions being equal, if we take a look at this chemical reaction, we have 2 reactants here, one larger purple sphere and one smaller one. They combine together going in the forward direction. Together when they combine they become this more like pinkish type of compound. Now here since we're talking about the forward direction, we look at the rate of the forward direction. But since we're talking about chemical equilibrium, there's a chance of this react of this product that's been formed that some of it moves backwards and reforms our reactants. Here, we're going to say at equilibrium, the rate of the forward reaction equals the rate of the reverse. That means there is no net change in concentrations. So basically we are losing some reactants to make products, but then some of that product goes in the reverse direction to recreate our reactants. So there's no real change in the amount of products and reactants. For the amount that we're losing, we're gaining it right back. Now here if we took a look at this, this graph here, we're going to say that this purple line represents our reactants. Remember, we break down reactants to help us reassemble them into products. Because of this, we're going to see a gradual decreasing of our reactants up to this point of 15 seconds. And then this pinkish fuchsia color is our products that's being formed. Initially it starts off as 0 because at the beginning of a chemical reaction there is no product. We're going to start making product, and eventually it's going to hit this point here: 15 seconds. That 15 seconds represents where equilibrium has been established. And if we're at chemical equilibrium we have a reversible reaction. So they're moving forward and backwards, thereby there is no net change in our concentrations. Which is why we see for the most part the level of reactants and products kind of staying constant. Now if we wanted to think of this in real world aspects, we could think of a party. In the party, we have a combination of people who represent products and reactants. We can say that we have products and react to 1 of each, leaving the party to go outside, but as they leave we have another set of products and reactants entering the party. So nothing is really lost or gained. There's no net change in number of people. 2 left, but 2 came back in. Now here we're going to say that chemical equilibrium can be either homogeneous or heterogeneous. Now when we say homogeneous we're talking about homogeneous equilibrium. This is where reactants and products are present in the same state of matter. So basically all the compounds within the chemical reaction are gases, or all are aqueous, or all are liquids or solids. It's a one type of phase, they're all the same. In a heterogeneous equilibrium we have reactants of products that are in different phases. Maybe our balanced chemical reaction has a mixture of solids and gases present. That represent a heterogeneous equilibrium. So remember, when we reach chemical equilibrium, there is no net change in the amount of reactants and products. Whatever is lost is being regained because we are a reversible reaction.
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example
Intro to Chemical Equilibrium Example
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1m
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So describe what happens to a reaction when it reaches chemical equilibrium. Now here for A it says the reaction stops, Remember we said that in a dynamic process the reaction doesn't simply stop, so A could not be an answer. B. Reactants form products as fast as products form reactants. This is an answer. Because remember when we get to chemical equilibrium we have a reversible reaction. Meaning the rate of the reverse and the rate of the forward reaction are equal to one another. So the pace at which reactants or products are being formed is equal. This leads to no net change in the concentrations of either your reactants or your products. Here the collision frequencies of products and reactants are equal or identical. We never went into this detail, so we don't know for certain that this contributes in the same way that our rates would. Okay? And because of that, we can't say it's a viable answer. 4d, rate of forward and rate of reverse reactions are equal to 0. This would only happen if the reaction stopped. And again, since we're at equilibrium, it's a dynamic process so the reaction doesn't stop. They wouldn't be equal to 0, they'd be equal to one another. So out of all the choices given, only option B is the correct answer.
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Problem
Problem
Which of the following does not represent a heterogenous equilibrium?