7 posts • Page 1 of 1
In class, we went over a problem where we needed to calculate the temperature needed to make the reaction spontaneous. I understand that delta G needs to be negative for the reaction to be considered as such. We got 333K by setting the delta G to 0, but would that be the final answer? Or would the answer be anything higher than 333K, because then that would make delta G negative?
Setting T = 333K is not the final answer; it's the "boiling point." But it is necessary to find that value to come up with the final answer: T > 333K favors the forward reaction and makes delta G negative.
With the information that we had, we were forced to solve for G = 0, which gives us the boiling point at which the liquid will become a gas. However, since it must be a gas, anything greater than 333K will be correct for this equation. Any higher temperature will result in G having a negative value, and when G is negative, the reaction is spontaneous.
Setting delta G to 0 merely gives the boiling point, in this case T=333 K. At this temperature, both the gas and liquid phases exist; therefore, the forward reaction isn't favored until T>333 K, causing delta G to be negative. If finding the boiling point by setting delta G to 0 complicates the calculation, I suppose you can just create an inequality: 0 > delta H - T(delta S) so that you can go directly to final answer by solving for T.
Because we are solving for a single variable (T) and there are two unknowns (T and G), we set G=0 in order to find the boiling point at which the liquid and gas state can coexist. Once we find the T at which they coexist, we know that a T higher than the one we found will allow for only gases to exist, which tells us when the process is spontaneous (G will be less than zero, or negative, at that point)
Who is online
Users browsing this forum: No registered users and 2 guests