Entropy Ch19 V2

本站添加: 2026-05-16

[00:00:00]okay so we're gonna go over to second law of thermodynamics the second law of thermodynamics is the one that explains why when you put a hot and cold object the hot object gets colder the cold object gets hotter and not the other way around because if it went the other way around if your coffee that you put on the table got hotter and the table got colder as long as the energy transfer from the cold object to the hot object like if the cold object lost 20 kilojoules on the hot object gained 20 kilojoules as long as that was the same then the first law is obeyed there is nothing the first law that says that the hot object must lose heat Nicole one must absorb it it's the second love and it explains that it has to be probability so when you put a hot object in a cold object next to each other the chances of a molecule and a cold object moving slow and a molecule with a hot object moving fast the chances of that collision where the energies transfer from the hot object to the cold object because this is moving stored is moving faster state transfers energy from the hot to the cold will be higher than the other way around and that's why generally what happens is the hot object loses heat and the cold one gains it so the second law of thermodynamics says the entropy of the universe increases in a spontaneous process and remains unchanged in a equilibrium process so any process that is spontaneous has the higher chances of taking place that's why it happens just like every time you buy a lotto ticket you lose it's because the probability of losing is much higher than winning and so that's pretty much probability at work every time you call after you clean it gets messy after a month or your room same thing again has to do with entropy in a probability of it getting unorganized and Messi's much higher than its remaining organized so anyways that time you showed that Delta s universe is equal to Delta s system plus Delta s running against system is the part of the universe that were interested in surroundings is anything outside of that and so now let's go over and calculating entropy changes in a system like a chemical reaction so if you have a chemical reaction you want to calculate that change in entropy of that it's very similar to change in enthalpy so it would be the sum of the entropy of products minus the sum of entropy of reactants that hollow circle means under standard states standard states again is when you have both the reactants and products present if the reactants are aqueous or concentrations should be 1 molar if the products or reactants are aqueous if the products or reactants are gaseous their partial pressures should be one atmosphere and if they're solid or liquid they must be pure and generally temperature is 25 degrees Celsius now we can make some generalizations due to gas as having much higher entropy than solids and liquids if agree since gases have much much higher entropy and to calculate the change in entropy a reaction you take product minus reactant if the reaction produces more gaseous products than it consumes then the Delta s for that reaction will be positive because this value will be bigger than this so this minus that will be positive and that's similar to for example taking papers or files in your room or clothing on of the your dresser and basically on in the closet and basically spreading them out all over the room because gases have much higher eventually when you make gases you're increasing the entropy lots of the Delta s is positive if you produce less gas molecules then you consume the Delta s is names like taking all those papers putting in two files and organizing things so how do we put this knowledge to work well let's say that we have these three reactions and we want to arrange them in terms of increasing entropy change so if you look at the first reaction the doctor and changing the number of gaseous molecules would be 1 minus 2 so that would be negative 1 so in this case we are organizing things Delta s will be negative here it would be 4 minus 2 so it's plus 2 so in here we're on organizing things about this will be positive and here would be 2 minus 4 so would be minus 2 sake and organizing things so in terms of increasing entropy the one that has the highest entropy would be reaction number 2 then it would be 1 if we're doing relative and then the third one so this would be increasing Delta s so you know you get questions like that word you need to figure out we're not doing any calculations motored all tests for the reactions positive or negative which reaction has a bigger positive Delta s than nature less negative innovation that's nice of it and then to actually calculated out let's say for this reaction calcium carbonate decomposing into calcium oxide and carbon dioxide it's not an equilibrium so I'm writing it this way and so in here again we take products minus reactants so one mole of calcium oxide it's entropy 39.8 because it's solid so it's entropy slow carbon dioxide is a gas it's actually is much higher so I take the coefficients I have one mole of this one mole of this so remember everything in chemistry is purple so if I have one more multiplied by one if there was a five here that I would multiply this by 5 and then for prop so these are products - we have the reaction is calcium carbonate 2.8 where do I get these values these are all from a table that you will be giving your exams and quizzes from so those are the standard entropy values for those substances and then you can look up in a table just like the enthalpy values then you look up in the table so then this value comes out as one sixty point five it's positive and we could tell it was positive because we're producing one roll of gas it's one minus zero so it's plus one so naturally should be positive entities 160.50 killing why is it joules per Kelvin you're gonna learn in the next video we're gonna go over how you can calculate that changing entropy of the surrounding as a result of what happens in this system but we'll do that in the next video