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# Standard change in free energy and the equilibrium constant

The relationship between standard Gibbs free energy change and the equilibrium constant K. Calculating K when you know the standard free energy of reaction.

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• I'm confused by the word "equilibrium". From the previous video it was said that at (delta)G = 0, the reaction is in equilibrium, But in this video, eventhought it question is asking for equilibrium constance, (delta)G = -33 kJ.
Well this is what I understand,
The "equilibrium" indicated by (delta)G = 0 is the equilibrium of spontaneity. It means by the energy and entropy of that environment, the reaction rate will be constant both forward and backward.
The "equilibrium" indicated by equilibrium constant K however, is the equilibrium of the concentration. It determines whether the reaction goes forward or backward depending on the qoutient (concentration of the products and reactants)
For instance,
ex1. the reaction has (delta)G = 0, the reaction still goes forward, if Q<K.
ex2. if Q < Kp (the reaction favours products) but (delta)G > 0, the reaction still doesn't occurs, since the reaction is not spontaneous. (unless, energy is added into the system)
ex3 if Q> Kp (the reaction favours reactants, but (delta)g<0 , the reaction occurs (spontaneous), but there are more reactants than products,

Am i understanding it right? please correct me if i'm wrong. • Equilibrium means that there is no observed change in the concentrations of reactants or products. Think about it as when the reaction has completed, even though it isn't exactly like that. For Example, for the equation:
N2(g) + 3H2(g) --> 2NH3(g)
at Equilibrium, the Reaction might not stop occurring, but the concentrations of N2, H2, and NH3 stay relatively the same.
The K value tells how much the concentrations of products and reactants there are.
If K >1, there are more Products than Reactants in Equilibrium.
If K=1, there are the same amount of Products as Reactants in Equilibrium.
If K <1, there are more Reactants than Products in Equilibrium.
Q is basically what the value of the the ratio of Products to Reactants before Equilibrium is established. so if
Q<K, the Reaction shifts to the Right,
Q>K, the Reaction shifts to the Left,
Q=K, the Reaction is at Equilibrium.
Delta G comes into Play when figuring out if the Reaction is Spontaneous.
when delta G>0, the Reaction is non- Spontaneous, but if
delta G <0, the reaction is spontaneous.
When K<1, the reaction favors the Reactants, so the Reaction is not Spontaneous, making delta G >0. but when K >1, the Reaction favors the Products, so it is Spontaneous, making delta G< 0.
delta G = -RTlnK
R=8.31 Joules/(mole*Kelvin)
Hope that clears up some of your confusion!
• Why the ΔG0 has different values if the temperature is always T=298 K ? • What is Standard change in free energy? • I thought dG0 was a constant for the reaction at 25C. To then find the new equilibrium at a new temperature you take e^(-dg0/(RT))... Why does dg0 change in the different examples for the same reaction? • Is ΔG only applicable to reversible chemical reactions? • converting from kj to J don't you just divide by 1000 because for every 1 Joule there is 1000 KiloJoules? 106.5kj x (1/1000)= 0.1065. As I see in the video you just made 106.5kj into 106.5x10^3 Joules. I am just confused because when I cancel out units I should be dividing by 1000 not multiplying.
(1 vote) • The best thing to do is use dimensional analysis rather than trying to remember when to mulitply and when to divide. With dimensional analysis, you multiply by the conversion factors in such a way as to take what you started with and get the units to cancel until you get what you wanted. Thus, to convert kJ to J you do the following:

1 kJ × (1000 J / 1 kJ) = 1000 J
Notice that the `kJ` cancel out and you're left with `J` as you units.
You can use dimensional analysis for many of the processes in Chemistry.
• I’m a bit confused about Kp and Kc, how can they be equal since isn’t the formula the Kp is Kp=Kc(RT)^delta N(N is the coefficient of the elements) and N is clearly not 0 here • Hi, how can I link equilibrium to the effectiveness of hot and cold packs? • Interesting question! The central idea here is that systems will always tend toward equilibrium. So if there is a difference in temperature between two entities that are in contact, heat will flow from the hotter entity to the colder one; this decreases the temperature of the former and increases that of the latter until both are at the same temperature. For instance, if you are cold and apply a hot pack to your skin, some heat from the hot pack will flow to your skin, and thus you will get warmer and the hot pack colder. Of course, this process will only occur until your skin and the hot pack are at the same temperature and then there will be an equilibrium, which means not net change in temperature between the two systems. Heat will still flow between the hot pack and your skin, but now at the same rate in both directions, so there is no overall change at equilibrium.

The inverse of the above process occurs with the cold pack, expect in this case your body is the heat donor and the cold pack the acceptor. :)
(1 vote)
• So when delta G = 0, what does that tell us about the free energies of the reactants and products? They have the same magnitude but opposite charges? If so, how's the reaction still going in both directions? Is the reaction spontaneous in both directions?  