is if Delta H is negative and Delta s is positive okay they can both be positive they're gonna both be negative those are two scenarios one it could be positive one can be negative and they can switch so there's really only four scenarios okay if this happens okay let's think about our equation again here's our equation Delta G equals Delta H minus T Delta s so if Delta G is Delta H and Delta H is negative - minus T temperature and Delta s is positive - a positive okay you can make up some numbers to prove this to yourself but if you subtract a positive value from a negative number it will always be negative okay so like negative ten minus positive five negative 15 negative 100 - negative - positive 600 negative 700 okay it's always going to be negative Delta G is negative at all temps because of the temperature because we're doing it in Kelvin or using your we're going to do the calculation in Kelvin that will never change the sign okay so if it's negative at all temps what does that mean is it spontaneous or non-spontaneous it's negative spontaneous yep so Delta G is spontaneous at Delta G sponte the reaction is spontaneous at all temperatures and if you think about it both of these were the two scenarios were the reaction tend to be spontaneous if we're exothermic that means we're going downhill in terms of potential energy tend to be spontaneous if our Delta s is positive that means we're becoming more disordered which is most likely happen so both of those happening cause the reaction to be spontaneous at all temperatures on the other side of the spectrum you could have a reaction or physical process where Delta H was positive and Delta s is negative well will that do for our calculation now we got Delta G equals a positive number and we're gonna subtract a negative number which will turn it into a positive so we're taking a neg positive number subtracting a negative number which turns it positive so guess what you're going to get a positive number no matter what you do you can put any numbers in here have at it test it out this is going to happen Delta G is positive at all temps so what does a positive Delta G mean non-spontaneous and so this reaction or chemical process or physical process is non spontaneous at all temperatures then again if you think about this conceptually the two variables that's being an entropy this should make sense so I've changed now to sweet Delta H is positive what do we call that type of reaction endothermic so of course that means you have to put in energy for that to go or they know you don't have it's going uphill in potential energy so the surrounding is transferring energy to this system the reaction Delta s is negative what's that mean Delta s is negative what's that mean it's becoming order it's becoming less disordered or becoming ordered and we know that takes energy to do that nature doesn't tend to order things it tends the disorder them and so both of those are the cases where it tend to be non spontaneous and when they're combined there gonna be someone on spontaneous at all temperatures okay so those are the two ones that are sort of invariant of temperature the next two are going to be temperature dependent there'll be a temperature at which they become spontaneous or non-spontaneous the first of those that we could talk about is let's say they're both positive to Delta H is Z that were positive so it's endothermic not good for spontaneity and Delta s is also positive so that's becoming more disorder so that's good for spontaneity endothermic bad for spontaneity increasing entries good so which ones out well it's gonna be temperature dependent so its thing about this Delta G equals a positive minus T a negative positive I mean so it really depends which is going to be bigger all right and so there's going to be two scenarios at a low temperature and high temperature so let's just play around with some numbers all right so let's say at low temperatures let's say T equals zero point five Kelvin so that's low that's cold all right give crabber jackets okay let's just make up some numbers all right so let's say our Delta H is 10 kilojoules and our Delta s is 2 kilojoules per Kelvin all right just making up numbers so what's gonna happen at the low temperature Delta G is going to equal 10 minus 0.5 Kelvin times 2 kilojoules per Kelvin that equals 1 10 minus 1 is 9 kilojoules that's positive right so what's that mean non-spontaneous now let's think about at high temperatures say tamp equals I don't know 20 Kelvin that's still pretty cool grab your jacket a scarf and prepare to die that's really cool but anyways it's it's gonna work out for this example again I'm just making up numbers so we're gonna keep our Delta H and Delta s the same so Delta G's can equal 10 kilojoules minus 0.5 times oh wait no let's screw this up let's make it a little bit warmer 40 kelvins I've got to make it work so I can make a point at the end so if it doesn't make the point that I want to make it it's not gonna be a good example all right so times 40 uh no wait all right no no no they did you do oh that was okay let's go back to 20 start over it's gonna look good in the video it's gonna look like I know what I'm doing okay so a 20 Kelvin so get 20 Kelvin times 2 kilojoules per Kelvin so 10 minus 20 times 2 that's 40 10 minus 40 is negative 30 kilojoules what's that mean if Delta G is negative spontaneous so at high temperatures this reaction would be spontaneous yes sir sandir States 25 degrees Celsius 1 molar concentrations one atmosphere partial pressures so and now the real the real point I'm making here not with the actual numbers is that for this system where the enthalpy is positive and the Delta s is positive there's going to be a temperature at which this reaction or physical process become spontaneous all right and for this one it's going to be at low temperatures it's not spontaneous at higher temperatures it is spontaneous all right a good example of that is something really simple water boiling or water melting it could be either one but I already said water boiling I'm going with it all right at what temperature does water boil 100 degrees Celsius 373 Kelvin below that temperature it's not spontaneous above that temperature it spontaneous okay and that is a good example because well of course that's a good example I came up with it no but that's exactly the scenario here it's blowing so what do you have to do to it to boil water you got to put on your stove or on the hot plate in the lab right so you have to put energy into it it's an endothermic process but the water is going from the liquid phase of the gas phase what's happening to entropy it's increasing Delta s is positive you have to put so all endothermic means is that the energy is transferring from the system surroundings to the system that's what you do when you boil water at atmospheric pressure 25 degrees Celsius okay all right so there's gonna be one more possibility both 1 negative 8 is negative Delta is positive Delta H is positive Delta Delta s is negative they're both positive and of course both negative ok so the last one is if Delta H is negative good for spontaneity coming downhill in terms of potential energy and Delta s is also negative meaning becoming less disorder more order not good for spontaneity all right so this isn't going to be another one or its temperature dependent all right so again we're gonna have at low temperatures so let's say T equals one Kelvin all right we're cooking now want Kelvin all right we got to make up some Delta H is so it's a Delta H is negative 20 kilojoules and Delta s is negative 5 kilojoules per Kelvin okay so at low temperatures Delta G equals a negative 20 Delta H kilojoules minus T Delta s so temperature one Kelvin a negative five kilojoules per Kelvin that equals negative 20 minus a negative five so it'll be plus 5 so negative 15 kilojoules so what's that mean spontaneous that's the low temp all right so let's see what happens at a higher temp let's say temperature equals so we got to be higher than one Kevin let's say 100 Kelvin whoo sizzling no still really really cold but it's higher for this example I wouldn't want to go into that place whatever so it's minus a negative 173 Celsius so Kelvin minus 4 from Celsius to Kelvin you add 273 subtracted from Kelvin so negative 173 Celsius as being American I have no idea how cold that it's by nose cold it's funny when I like try to like pretend I know Celsius and like say what temperature it is outside it's always like really it's like I don't know 40 degrees Celsius outside it's like 120 Fahrenheit ish I don't know I try so what so the room temporal sink I mean I can get a better guess at that so you know it's 25 degrees Celsius is about 72 Fahrenheit so it's like 80 degrees maybe like 27 28 outside all right see I can fake it fake it till you make it or in my life okay so at higher temperature what's gonna be our Delta G I bet you're gonna ya bet you could predict this so it's still negative 20 kilojoules - now we're at a hundred Kelvin T times Delta s so a hundred Kelvin times a negative five kilojoules per Kelvin so that's negative twenty minus a negative five hundred so plus 500 so what's that plus 480 kilojoules what's that mean non spontaneous we can it's good oh yeah for this yeah we'll do an example I'm glad yeah I'll talk to you later it's not spontaneous at high temperatures okay again I'm just making them numbers to prove the the math behind this and so for a system where the enthalpies negative exothermic and entropy is negative meaning becoming more disordered again it's temperature dependent but this time the process will be spontaneous at a lower temperature and non spontaneous at a higher temperature basically the antal P has to make up for the decreasing entropy the system is becoming more ordered so the enthalpy has to disorder the surroundings enough to make Delta s positive so we can follow the second law of thermodynamics and of course we know that the change in entropy is going to make a bigger difference at a lower temperature we saw that previously alright so what's an example that another simple example would be water freezing and I know I definitely know how to spell freezing and that's not it so what's water freezing what's the physical process what's going on liquid to solid [Music] so we're becoming more ordered we're going from liquid water molecules randomly around the sample to now they're in fixed positions in a crystal and so archery is definitely decreasing but it's also accessor m'q and so below what temperatures water freezes at zero degree Celsius so below zero degree Celsius 273 Kelvin it's spontaneous above zero degrees Celsius 20 273 Kelvin it's non spontaneous