The reaction A21g2 + B21g2 ∆ 2 AB1g2 has an equilib- rium constant Kc = 9. The following figure represents a reaction mixture that contains A2 molecules (red), B2 mol- ecules (blue), and AB molecules. What statement about the mixture is true? (LO 15.5)

(a) The mixture is at equilibrium, and there will be no net shift in reaction direction. (b) The reaction will shift toward the reactants to reach equilibrium. (c) The reaction will shift toward the products to reach equilibrium. (d) More information is needed to answer this question.

Video transcript

Hi everyone. This problem reads consider the following reaction with an equilibrium constant of 0.25. The diagram below shows a mixture of the molecules L two, M two and L M determined the correct statement about the mixture. Okay, so we have four statements here and let's take a look. These statements have to do with the reaction shifting. Okay, so because we're dealing with statements that are discussing the shifting, we need to compare Q and K. So depending on if Q is greater than or less than K, our reaction will shift to obtain equilibrium by reaching the equilibrium constant K. So if Q is equal to K, let's go ahead and write this down. If Q is equal to K. This means the reaction is at equilibrium. If Q is less than K. This means the reaction is going to shift in the forward direction to establish equilibrium and if Q is greater than K. This means the reaction is going to shift in the reverse direction to establish equilibrium. Alright, so now what we need to do is we need to we know what the value of K is. Because it was given in the problem, the equilibrium constant K Is equal to 0.25. So what that means then is we need to calculate the cute value. Alright, so to do that, Q is going to equal the concentration of products over the concentration of reactant. So we need to look at our equation. Okay, so looking at our equation, our products are L two and M two. So it's going to be the concentration of L two times the concentration of M two over the concentration of reactant and the reactant is L. M. Okay. And we have to look at the coefficient in front of it because that becomes an exponent. So now that becomes L M squared. Okay, so looking at the picture, we're going to plug in what we see for the values. Okay, so for Q we see that L and M. There are five each. Okay, so we're going to get five times five and for L. M there are four and we're going to square that. Okay, so what that means is the value for Q when we saw for this is 1.56 and we see that Q compared to K. Q is bigger and based off of what we wrote when Q is larger than K. The reaction is going to shift in the reverse direction to establish equilibrium. So let's take a look at our statements Okay, statement A The reaction shifts in the four direction to produce more products until equilibrium is established. This is incorrect because we just said the reaction is going to shift in the reverse direction, statement be the reaction shifts in the reverse direction to produce more reactant until equilibrium is established. This is correct. Okay. And let's take a look at see the reaction mixture is at equilibrium. No, it would only be at equilibrium if Q is equal to K and in this case it is not Andy not enough information is given is incorrect. So our correct answer here is B. And that is it for this problem. I hope this was helpful.