so let's look at this example calculate delta g we've got a new handy dandy equation we know how temperature affects it the spontaneity we know whether or not it's spontaneous or not now let's just calculate it so let's try example 17.3 consider the following a reaction for the decomposition of carbon tetrachloride gas all right so let's calculate Delta G at 25 degrees Celsius here's the enthalpy and here is the entropy all right so this is not too bad we're going to determine whether or not it is spontaneous so Delta G is Delta H minus T Delta s okay our enthalpy is right here plus 95.7 kilojoules minus temperature 25 degrees Celsius right 95 degrees Celsius I'll just write that right here plus 2 I should convert it to Calvin oh yes we probably should convert it to killin 298 times my Delta s Delta s is right here plus 142 point 2 joules per Kelvin rot Rho got changeit kilojoules right if my Delta H is in kilojoules and it's usually reported to kilojoules and my Delta s is only in joules and it is usually reported to in joules I got to make them match so I can add and subtract them right 0.14 - okay that is again usually the case because entropy changes are a lot smaller than it will be changes so Delta s is usually reported to in just joules antipas reported - in kilojoules because it's usually a lot larger so joules per Kelvin and if I want to convert that to kilojoules how many joules are in a kilojoule 1,000 started writing it before asset so I probably just tell you you knew that all right so that is going to be 0.14 - to kilojoules per Kelvin do you think I need the whole Bluetooth wireless earpiece or should have just text well you don't want that like this kind of setting plus you don't want to know people you're using the per diem pen you know they want you to know that you want people to think that you can spell very good well each spell well see yeah that's why I need the per diem pen spell goodly good I felt good see all right so what do we get for Delta G to the per diem pen what I already told me I'm sorry positive 53.3 what are my units kilojoules no the kelvin cancel so we're left with the kilojoules well it's at addition and subtraction so it's not so I got a fifty three point three then I got a 91 good three 53 53 so let's determine whether the reaction is spontaneous or not is it spontaneous or non-spontaneous non spontaneous which we really should have realized or predicted look at be if the reaction is not spontaneous here's more work come on TRO come on TRO he had he had us trapped alright so yes that it's not spontaneous now that we know it's non spontaneous determine at what temperature if any the reaction become spontaneous and here's where we can calculate what temperature it becomes spontaneous now well how are we going to do this well if it's positive it's non spontaneous if it's negative its spontaneous right so what happens in the middle it equals zero all right and that would be at equilibrium so that's like the tipping point whenever Delta G equals zero that's when it can turn spontaneous or non-spontaneous depending on increasing or decreasing the temperature so to solve for the temperature at which it becomes spontaneous you set Delta G equal to zero and solve for the temperature so Delta G equals zero we got zero equals Delta H minus T Delta s let's add T Delta s to both sides shall we good so T Delta s equals Delta H then what do I do divide both by Delta s okay so we got temperature equals Delta H over Delta s and then we can calculate we've already got our enthalpy and our entropy our enthalpy was a positive 95.7 kilojoules or Delta s and we are gonna have to one use the one we converted into kilojoules so it's plus point one four two two kilojoules and so we can take 95.7 / 0.14 to - 673 what are my units Kelvin kilojoules cancel out leaving me with Kelvin so this reaction becomes spontaneous