hello everybody my name is Iman welcome back to my YouTube channel today we're covering chapter three for MCAT physics and this chapter is going to be about thermodynamics now thermodynamics is the study of the flow of the energy in the universe as that flow is related to work heat entropy and different forms of energy now we're going to explore thermodynamics by covering the following four objectives we're going to start with the zero with law of thermodynamics and here we're going to discuss temperature in detail and learn to convert between three units of temperature Celsius Fahrenheit and Kelvin and this is going to be followed by a discussion on thermal expansion now the second objective we're going to move into discussing systems here we're going to learn about open closed and isolated systems in addition to the difference between State and path functions third we'll cover the first law of thermodynamics here we're going to talk about heat we're going to talk about heat transfer we're going to talk about heat transformation we will also cover different thermodynamic processes like isothermal isobaric isochoric and adiabatic last but not least we're going to cover the second law of Thermodynamics and here we're really just going to have an in-depth conversation about entropy all right now the hope is to be able to understand the laws of thermodynamics and we're not going to cover that third law in detail there's not much to it but we'll Define it as we talk about temperature since it makes sense all right and by the end of the chapter you'll be able to understand and be able to express and Define all of these laws of thermodynamics with that we're going to get started with our first objective and that is defining and understanding the zero with law of thermodynamics now the zero with law of thermodynamics is the principle that if two systems are each in thermal equilibrium with a third system then they are in thermal equilibrium with each other so what we're saying is if block a is in thermal equilibrium with Block B and Block B is in thermal equilibrium with Block C so a is in thermocular room with B B is in theorem of equilibrium with C then we can directly say that c and a are also in thermal equilibrium all right the zero with law of thermodynamics is the principle that if two systems are in thermal equilibrium with a third system then they are in thermal equilibrium with each other and this law establishes the concept of temperature and is a fundamental principle of thermodynamics now in other words I suppose the zeroth law of thermodynamics is based on a very simple observation all right so that one one object is in thermal equilibrium with another all right say these blocks or say a cup of warm tea and okay yeah say a cup of warm tea all right and a metal stirring stick all right are in thermal equilibrium with each other all right and the second object is in thermal equilibrium with a third object say your hand holding that cup all right then the first and third objects are also in equilibrium so your metal rod and your cup of tea are in equilibrium your hand and your and the cup are in thermal equilibrium then by the zeroth law your hand and that metal stick are also in thermal equilibrium as such when brought into thermal contact no heat will flow between these objects because they're already in thermal equilibrium note that thermal contact does not necessarily imply physical contact as objects can be in thermal contact across space so even though your hand is holding the cup and not the stirring metal stirring stick they are still in thermal equilibrium now this this third law of thermodynamics which we're not going to have a whole objective on but I'm going to Define here this third law of thermodynamic it establishes the concept of temperature and an understanding of temperature is going to be really important to navigate thermodynamics um this third law of thermodynamics says that entropy of a pure crystal is zero as the temperature of approaches absolute zero all right so that's the only definition and thing we need to know about the third law of thermodynamics but it ties in this concept of temperature and this formulation of the zero with law actually right that states that no net heat flows between objects and thermal equilibrium all right and the um following thing that heat flows between two objects not in thermal equilibrium actually arose from studies of temperature so at any given time all substances they have a particular temperature in everyday language we use the term temperature to describe qualitatively how hot or cold something is but in thermodynamics when we talk about temperature it has a more precise meaning at the molecular level temperature is proportional to the average kinetic energy of the particles that are going to make up that substance at the macroscopic level it is the difference in temperature between two objects that are going to determine the direction of heat flow all right so when possible he is going to move spontaneously from materials that have high temperature to materials that are going to have low temperature all right that is what's going to happen all right spontaneously all right now heat itself heat itself refers to the transfer of thermal energy from a hotter object with higher temperature AKA higher energy all right to a colder object with lower energy AKA lower temperature all right now if no net heat flows between two objects in thermal equilibrium then we can see that their temperatures are equal and therefore they are in thermal equilibria now since the 18th century scales have been developed to quantify the temperature of matter with thermometers some of these systems are still in common use like the fahrenheit system or the Celsius system and even the Kelvin system all right Fahrenheit and Celsius are actually the the oldest systems the oldest skills um still in common use and they are relatively convenient because they're actually based on the phase changes for water so in the Celsius scale all right in the Celsius scale 0 degrees Celsius zero degrees Celsius is defined as the freezing point of water all right so in the in in Celsius zero degrees is the freezing point also in zero degree F also in Celsius 100 degrees Celsius is the boiling point of water all right and so in the Celsius scale 0 and 100 Define the freezing and boiling points of water respectively now in the Fahrenheit scale all right these phase changes these phase change temperatures are defined as 32 32 degrees Fahrenheit that's the freezing point for water in the Fahrenheit scale and the boiling point of water in the Fahrenheit scale is 20 212 Fahrenheit all right now in the Kelvin scale all right this Kelvin scale it's most commonly used for scientific measurement it's actually one of the seven SI base units that we talked about in the first chapter it defines as the zero reference point it defines it as the absolute zero so the theoretical temperature at which there is no thermal energy that's going to be your absolute zero so it defines as the zero reference point absolute zero that's the theoretical temperature at which there is no thermal energy and it sets the freezing point of water then at 273 Kelvin so we can see here that 273 Kelvin is the freezing point and 373 degrees Kelvin is the free is the boiling point of water all right now again here the third law of thermodynamics it states that the entropy of a perfectly organized Crystal at that absolute zero in the Kelvin scale is zero all right it's entropy of a perfectly organized Crystal at Absolute Zero is just zero note that there's there's just no entropy for a perfectly organized Crystal at Absolute Zero all right so that's the Celsius Fahrenheit in Kelvin they're the most commonly used temperatures all right they're the most commonly used systems for temperature now while we won't cover while we won't cover the third law of thermodynamics past this definition all right there's one important thing to note about Kelvin what you'll know is that there are no negative temperatures on the Kelvin scale because it starts at absolute zero all right and although the Kelvin and Celsius scales have two different zero reference points the size of their units is the same that is to say that one chain that a change of one degree Celsius equals a change of one unit Kelvin it's going to be important also for us to know how to enter convert between these units all right and so we see these formulas here that I've written on these notes for under each category that's going to help us convert between different units all right so Celsius how do we get celsius if we have Fahrenheit we can use the following expression here five over nine all right parentheses Fahrenheit minus 32 degrees that will get a Celsius for Fahrenheit if we want to get Fahrenheit that's going to be equal to 9 over 5 Celsius plus 32. all right now if you just remember one of these pick one or the other that's easier to memorize you can get the other very easily by shifting things around for example if you memorize this Fahrenheit equation Fahrenheit equals 9 over 5 Celsius Plus 32. all right and you're trying to get the equation for Celsius easy all you have to do is move things around we can move minus 32 to the other side all right so then we have Fahrenheit minus 32 is equal to 9 over 5 Celsius and then we want to multiply both sides by 5 over 9. all right and then what we get is that Celsius is equal to 5419 Fahrenheit minus 32. see how by memorizing just one we can easily move things around to solve for for Celsius even though we started with a fahrenheit definition all right it's very easy to shift things around to redefine your variables all right and kelvin's really easy Kelvin is just Celsius Plus 273. all right now with that being said we're only going to really learn this if we do a practice problem all right so let's move over here and do a practice problem really quickly okay this says if a meteorologist says that the temperature will reach a high of 86 Fahrenheit today what is that number in Celsius and what is that number in Kelvin all right so we have the temperature in fahrenheit we want to figure out what the temperature is in Celsius and the equation for Celsius is five over nine Fahrenheit minus 32. all right so we want to go ahead and plug things in here all right so let's go ahead and do that all right five over nine Fahrenheit is 86 minus 32. all right and now we're gonna calculate this using our calculator all right 86 minus 32 that's going to be 54 and so that's 5 over 9. over 54. all right now this is going to be make this uh calculation very easy because 9 and 54 are both divisible by 9. so we can divide 9 by 9 that's 1 and 54 by 9 that's 6 and all we're doing now right now is five times six and so this is 30 degrees Celsius all right 86 Fahrenheit is equal to 30 degrees Celsius now if we're trying to find Kelvin kelvin's really easy it's just Celsius plus 273 and that gives us 303 Kelvin fantastic all right so to summarize what we've talked about is the zero with law which states that if two thermodynamic systems are in equilibrium with a third then the two are in equilibrium with each other all right in short temperatures the physical property of matter related to the average kinetic energy of particles and we have discussed the Fahrenheit Celsius and Kelvin systems for temperature and now we have learned how to interconvert between them with all this information we're going to move on to discussing thermal expansion all right thermal expansion it has long been noted that some physical properties of matter change when the matter gets harder or colder length volume solubility and even the conductivity of matter it changes as a function of temperature this relationship between temperature and a physical property of some matter was used to develop the temperature scales which we're familiar with actually alright so this Fahrenheit Celsius Kelvin scales they were extracted from observing this relationship between temperature and a physical property of matter now while we don't need to cover the way that thermometers and temperature scales are developed we can cover the important takeaways all right Daniel Fahrenheit he developed the temperature scale that bears His Name by placing a thermometer all right he placed the thermometer into some filled volume with Mercury all right into a bath of ice water and ammonium chloride and in this case the height of a column of mercury can be correlated to certain temperature marks such as the phase change for water and once the scale has been set in reference to the decided upon temperature marks then then the thermometer can be used to take the temperature of any matter in accordance with the zero with law now because that property of thermal expansion was integral into the development of thermometers let's actually take a little more let's take a closer look at this phenomenon all right a change in the temperature of most solids is going to result in a change in their length and so Rising temperatures they cause an increase in length and falling temperatures cause a decrease in length the amount of length change is going to be proportional to the original length of a solid and the increase in temperature accordingly to this equation that's written right here all right this equation says that the change in length Delta L is equal to the coefficient of linear expansion multiplied all right by the original length and the change in temperature all right and so this expression is going to help us calculate the change in length all right as we vary temperature all right this coefficient of linear expansion is a constant that carry characterizes how a specific material's length changes as the temperature changes all right this usually has a unit of inverse Kelvin although sometimes it can be coded as inverse Celsius all right the difference this difference is inconsequential because the unit size for the Kelvin and Celsius scales at the same all right the the scale the same all right now in addition to that liquids also experience thermal expansion but the only meaningful parameter of expansion is volumetric expansion or volume expansion the formula for volumetric thermal expansion is applicable to both liquids and solids and we can see the formula here change in volume is equal to the coefficient of volumetric expansion multiplied by the original volume times the change in temperature again here the coefficient of volumetric expansion is a constant that characterizes how a specific material's volume changes as temperature changes all right let's do a practice problem all right to try to put what we just learned about these two thermal expansions and volume expansion formulas into effect all right this practice problem it states that a metal rod all right a metal rod of length two meters it has a coefficient of linear expansion of 10 to the minus 6 inverse Kelvin it's going to be cooled from one thousand eighty degrees Celsius to 80 degrees Celsius what is the final length of the rod okay perfect by using the information given in this one problem we can go ahead all right and say that we can use this formula right change in length is equal to the coefficient of linear expansion times the original length times change in temperature all right we have all these values Alpha is 10 to the minus 6 Kelvin original length is 2 meters and we're changing change in temperature final minus initial that's how we do it 80 minus 1080 degrees Kelvin all right now they say Celsius here but again we said this difference between Kelvin Celsius inconsequential because the unit size for Kelvin and Celsius scales is the same all right they scale the same so we can do this all right now we plug this into a calculator what we're going to get is minus 2 times 10 to the minus 3 meters this negative sign represents a decrease in length all right so this metal rod is going to decrease from 2 meters all right the original length was 2 meters therefore the final length is going to be 2 meters minus 2 times 10 to the minus 3 meters all right and that's going to give 1.998 meters all right so that's the final length of the rod as the temperature is cooled from 1080 to 80. all right so that's how you want to approach this kind of problem all right let's do one more all right suppose that a thermometer with one milliliter of mercury is taken from a freezer with a temperature of minus 25 degrees Celsius and it's going to be placed into an oven of 225 degrees celsius if the coefficient of volumetric expansion of mercury is 1.8 times 10 to the Kelvin times 10 to the negative 4 inverse Kelvin by how much will the liquid expand so we're going to write our formula change in volume is equal to coefficient of volumetric expansion times original volume times change in temperature all right let's plug in the values that we know they've given us everything we need beta is 1.8 times 10 to the minus 6 Kelvin it's one the volume is one milliliter and we're going from a 225 2 minus 25 degrees Celsius all right we're going our volume our final temperature is going to be 225 degrees Celsius our initial temperatures was minus 25 degrees Celsius so we do for delta T minus final minus initial all right final minus initial plug this into a calculator and what we're going to get all right what we're going to get here is 0.045 milliliters all right so by how much will the liquid expand by 0.045 milliliters all right with that we finish our first objective all right we're going to continue in the next video the rest of the objectives for this chapter if you have any questions so far about the zero with law and about thermal expansion leave them down below other than that good luck happy studying and have a beautiful beautiful day future doctors