 ## Biochemistry

Learn the toughest concepts covered in Biochemistry with step-by-step video tutorials and practice problems by world-class tutors

1. Introduction to Biochemistry

# Gibbs Free Energy

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## Gibbs Free Energy Equation 1m
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and this lesson, we're gonna cover Mawr Details about Gibbs free energy. Now, before we get to the other forms of the Gibbs Free Energy equations, let's first recall the standard Gibbs Free Energy equation and that relates the changes in free energy to the changes in entropy, temperature and the changes in entropy and recall that Gibbs Free Energy is the energy that's available to perform. Work and work is done in a reaction when the concentrations of that reaction or system change, and so recall that at equilibrium the concentrations of reactant and products do not change their constant. And so there's no work done at equilibrium, and the Delta G is going to be equal to zero at equilibrium. So this goes to show that the concentrations within a system influence the direction of a reaction. And so we're going to talk about in our next video, the reaction direction. So I'll see you guys in that video
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## Reaction Direction 5m
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So in our previous video, we talked about how the concentrations of a reaction impact the direction of that reaction. And so what's interesting to note is that cellular reactions are almost never at equilibrium, and this is due to several different factors, such as the conditions of the reactions changing and products being siphoned away into different reactions and reactant being constantly added. And so when a reaction is not at equilibrium, we need to make the appropriate adjustments. And one of those adjustments is to replace the equilibrium constant with the reaction quotient, which can be symbolized by the letter Q and notice that the reaction quotient expression is the same as the expression of the equilibrium constant. So it's the concentrations of products over the concentrations of react. It's and so the difference between the reaction potion and the equilibrium constant is that the equilibrium constant is specifically at equilibrium, whereas the reaction quotient is not at equilibrium. And so recall from your previous chemistry courses that last shot liaise principles so lush. Ali's principles state that when an equilibrium is disturbed, or when a reaction is not at equilibrium, such as cellular reactions, the reaction direction is going to proceed towards a direction to restore equilibrium so it will proceed to restore equilibrium. And so, in our example below, we're going to consider the reaction and then we're also going to complete the chart. And so in this reaction we have carbon monoxide gas interacting with hydrogen gas to produce methanol. And so again, recall that the reaction quotient expression is the concentration of products over the concentration of reactant. And so we only have one product here and that's methanol. So up here we can put methanol ch 30 h. Now, for the reactant, we have to react INTs the carbon monoxide which we can put over here. And we also have the hydrogen gas or H two. And again the coefficients, which is the two here, are expressed as, uh, exponents. And so we can go ahead and put this to Azan exponents here. And what you'll notice is that the reaction quotient expression is pretty much exactly the same as the equilibrium, constant expression. And the only difference is that the equilibrium, constants expression specifically has the concentrations of these substances at equilibrium, whereas the reaction question again is not at equilibrium. And so over here in this chart, where we're going to do is compare the reaction question with the equilibrium constant. Because if we know the equilibrium constant and we also know the concentrations of the substances at any particular moment in the reaction, we can predict the direction of that reaction. And so that's what we're going to do here. And so when the reaction quotient is smaller than the equilibrium constant, what that means is that the products are gonna be very small in their amounts, and the reactant are gonna be very large in their amounts. And so we'll have a whole bunch of reactant that's going to react and produce more product. So the reaction's gonna proceed in a forward direction. And so when the reaction question is smaller than the equilibrium constant, the reaction proceeds as written from left to right in a forward direction. Now, when the reaction question is larger than the equilibrium constant. What that means is that there there's a whole bunch of product and on Lee a little bit of reacting. And so we have a whole bunch of the product, and that's goingto go backwards and, uh, react to produce mawr of the reactant. And so when the reaction question is larger than the equilibrium constant, the reaction proceeds from right toe left in a reverse direction or a backwards direction. And, of course, when the reaction quote quotient is equal to the equilibrium constant, that means that we are at equilibrium and again at equilibrium. The rate of the Ford reaction is equal to the rate of the reverse reaction. So here we can put two arrows here showing that at equilibrium, the reaction rates are the same, going in both directions. And so what we're gonna see is what you're able to see is that, uh, the reactant and the concentrations of the reacting, some products, the concentrations impact the direction, and that is very, very apparent here. And so what's really important to note is that the concentrations are a part of the conditions of the reaction. And so in our next video, we're going to talk about how standard conditions impact the Gibbs Free Energy equation. And so I'll see you guys in that video
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## Gibbs Free Energy (Standard Conditions) 3m
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So from our previous video, we know that we can predict the direction of a reaction just by having the equilibrium, constant and the concentrations of reaction components. And so the concentrations are part of the conditions and scientists use standard conditions to allow them to compare different reactions under the same conditions. Since the conditions have a big impact on the reaction and this little symbol here, eyes used to represent standard conditions now recall from your previous chemistry courses that the equilibrium constant can be used to calculate the change in free energy under standard conditions. And so I recall that the little symbol here Delta, which is this triangle here, represents change. G represents the free energy. And again, this little symbol here not represents standard conditions. So this is the change in free energy under standard conditions. Now the Delta G without the not symbol represents the actual change in free energy under any conditions. And we'll talk about that one in our next video. So recall that standard conditions includes, uh, having a temperature at 25 degrees Celsius, which is equivalent to 298 kelvin. It also includes having a gas constant or are here, which is equal to 8.315 jewels per mole times, Kelvin. And so the gas constant, uh, magnitude. Here. The value of this number can actually change depending on the units. And so you might be familiar with a number 1.98 times 10 to the negative three. And this is when the units are in Q locales per mole times Calvin. And so it's good to be able to recognize that the gas constant can change depending on the units. And so the pressure, the atmospheric pressure under standard conditions is one atmosphere and the concentrations of reactant and products. The initial concentrations are one Moeller, and so you can see over here on the left that the Gibbs Free Energy understand Erred conditions is specifically shown as the following equation where the change in free energy under standard conditions is equal to negative are or negative gas constant times the temperature and units of Kelvin uh, times the natural log of the equilibrium constant understand erred conditions. And so we'll be able to apply this equation and some of our practice problems. Now, in our next video, we're going to talk about the Gibbs Free Energy under physiological conditions, which vary from standard conditions. So I'll see you guys in that video.
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## Gibbs Free Energy (Physiological Conditions) 8m
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Problem

Consider a reaction where Keq=1.6 but Q = 3.19. What direction will the reaction proceed?

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Problem

At equilibrium, the reaction A ⇌ B + C has the following reactant concentrations: [A] = 3 mM, [B] = 4 mM, and [C] = 10 mM. What is the standard free energy change for the reaction & is it endergonic or exergonic?

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Problem

ΔG˚=141.7 kJ for the following reaction. Calculate ΔG: T=10˚C, [SO 3] = 25mM, [SO2] = 50mM, & [O2] = 75 mM.

2 SO3(g) ⇌ 2 SO2(g) + O2(g) 