Gibbs Free Energy Nonstand Conditions Ch 19 V6

本站添加: 2026-05-12

[00:00:00]hello in this video you are going to look at Gibbs free energy for reactions that are not under standard states so we learn how to calculate that Gibbs free energy under standard states it was just Delta H standard minus T Delta s standard and that was when the concentration of reactants and products if they were there both reactants is our 1 molar products one will register aqueous if there were gaseous both reactants and products should be there their partial pressure should be one atmosphere there were solids or liquids they should be pure now what if the conditions are not standard because standard condition is just very thin slice one slice of time where you have those concentrations as soon as the reaction starts going those concentrations change but even before you may have different concentrations then how do you calculate Delta G remember it's the Delta G that tells you that a reaction spontaneous or not under displacement conditions not Delta G standard Delta G standard only tells you whether the reaction is spontaneous or not under standard conditions when the concentrations are 1 or the partial pressures of 1 atm but what if conditions were like that well in that case you calculate Delta G by taking out the G savage so you have to calculate Delta G standard to get the Delta G so you first calculate Delta G standard and then to it you add RT natural log of Q Q is the reaction quotient and if you have gaseous items then use their partial pressures in atm if you have a quiesce items then you use their concentrations molarity and T's temperature in Kelvin and R is that ideal gas constant 8.314 expressed in terms of joules so that's how you do it so we always wanted to calculate Delta G but in order to do that first day of calculate Delta G standard so then we can figure out Delta G and then from that figured out better reactions spontaneous or not so let's look at this example Delta G standard for this reaction we've counted in previous videos it came up to be a hundred thirty kilojoules per mole that means under standard conditions which means when we have pure calcium oxide pure calcium carbonate solids and partial pressure of co2 is one atmosphere above that and temperatures 25 degrees Celsius under those conditions the Delta G for this reaction we should call Delta G Stander's plus 130 kilojoule per one so that means that this reaction is not spontaneous and so in order to make it spontaneous you have to actually under those conditions put in a hundred kilojoules meaning one 100 kilojoules of work energy to form a work to get it to become spontaneous so now we want to figure out what is the Delta G if the partial pressure of co2 is lower than one atmosphere just like 1 times 10 to power minus PI minus y and the temperature is 25 degree Celsius well to calculate that it can be used a formula and I plug in the numbers and of course you're gonna convert this into kilojoules don't forget because this is in kilojoules so then the Delta G will be a little less positive it's 101 so that means that it's still non spontaneous under these conditions but not as much as before so under these conditions if you wanted to make it spontaneous we would have to put it only a hundred and 1.5 kilojoules per mole of work minimum to get it to become spontaneous right man hundred thirty whispers now what if we wanted to figure out what the Delta G is under these conditions which I don't know so for Part B now let's see if decrease the partial pressure of co2 and increase the temperature the reaction becomes spontaneous so now I am decreasing the partial pressure of co2 to 1 times 10 to the power minus 20 atm so you have very little co2 move there and the temperature increase to 100 degrees awesome so now I plug in the numbers that I saw and now we see that this term now becomes more negative than this is positive so overall the Delta G will be negative so these conditions the reaction is actually spontaneous so whether a reaction is spontaneous or not greatly depends on the condition of course so keep that in mind generally as a reaction proceeds and reactants get converted into products if initially the reaction is spontaneous as the reaction proceeds it becomes less and less spontaneous why because Q gets bigger and bigger and a skew gets bigger and bigger this term gets more and more positive so even if the Delta G standard initially is negative as this gets more positive it will become bigger than that and become 0 so in this case for example the reaction or these conditions is continuous but as it precedes creates more and more co2 so this partial pressure goes up so as that goes up this term becomes bigger meaning it will be less and less negative and then what happens is the reaction and reaches equal to it becomes