THERMOCHEMISTRY: Matter & Energy. Systems and Their Properties.

Added: 2026-05-11

[00:00:00]Hi guys. So, welcome back again. In today's video, I'm going to be teaching about thermmochemistry.

[00:00:20]chemistry and the basic concept about thermmochemistry is how the reactions how chemical reactions produce it, how reactions absorb it and how they evolve it during the reaction. Those are the basic thing that we are studying in the chemistry. So before we go into the chemistry, we need to know the meaning of matter and energy and the difference between matter and energy. Matter is there are tangible things around us.

[00:00:46]They occupy space like this is a matter the body is a matter I'm also a matter why energy is they intangible like you can't hold them you can't touch them but you can feel it like like love can be energy energy can also be in form of radiation it can be in form of heat which is the we are talking about in the chemistry so those are the two basic things about the chemistry the matter and energy. Another thing you need to know is the types of energy we have. We have the potential energy, we have the kinetic energy. Potential energy is the energy that is called the stored energy. When we put a let's say a ball on a table, the ability or the potential the ball has to fall down.

[00:01:40]That's the energy of like when it fall down. Let's say it falls down on a glass and it shatters the glass. Now it has the potential of falling down and shattering the gas. So that's the potential energy due to it position.

[00:01:53]While kinetic energy is just energy due to motion. So that's about that. You don't need to know much about potential energy and kindinetic energy when you're talking about the chemistry.

[00:02:03]But you also know the formula for energy which is half m² where m is your mass and v is your velocity and that of potential energy is mgh where m is your mass g is your accolation due to gravity and h is your height. So that's that about the energy and potential energy. So there are also basic concepts you need to know about thermmochemistry.

[00:02:33]You need to know what the meaning of a system surrounding the universe and boundary. So when I talk of a system, a system is just a system is just the the stuff we are studying like if you want to study this body, this body is our system. It is what we want to study. So if you are studying a particular reaction, the reaction we are studing is our system and the environment outside the reaction is our surrounding. So that's mean of surrounding and boundary.

[00:03:04]Boundary is just the it can be imaginary, it can be non- imaginary.

[00:03:08]It's just what separates the system from the surrounding. That's what boundary means. And our universe universe is an isolated system which means does an isolated system is a system that doesn't have interaction with the surroundings.

[00:03:22]So our universe like our planet universe our universe planet on planets the whole universe is an isolated system because we've not found what is outside our system what is outside our universe yet.

[00:03:34]So for now our universe is an isolated system.

[00:03:40]So another thing you need to know you talk about system about the law of conservation of energy. We all know the law of conservation of energy. You say energy cannot be destroyed. It cannot be created but it can be transferred from one place to another. It can be transferred from one form to another. So you can transfer potential energy but you can't create energy. Yeah. But why can create energy but you can't create energy? Energy cannot be created on a serious note. So that's the law of conservation.

[00:04:10]That's law of conservation of energy.

[00:04:12]And you should know that the you should note that the energy of our system the internal energy of our system the intern energy of our universe it is zero because intern energy is constant in our universe. Since it's an isolated system and it doesn't have any interaction now energy is not entering energy is not coming out because it's isolated is just in one place. So it is constant. So if intern energy is constant change in intern energy will be what? zero. Why?

[00:04:39]Because anything change I'm coming because anything change anything change is represented by delta delta. This stuff is called delta. So anything change means final minus initial. So if energy is constant so final energy is called initial energy. So final energy minus initial energy is what? Z. Let's say final energy is five. Initial energy is five. 5 - 5 is zero. So the change in energy of our universe is zero because the intern energy is constant system is what we are studying what we want to study our interest of study that's what we call system. So now let's talk about types of system we have a closed system we have the open system and have the isolated system but let me talk about the open system first. So when we talk about open system open in an open system matter can be exchanged and energy can also be exchanged. Let me explain what that mean is that let's say you have a container like this and this container there's a chemical reaction open this container and this container is opened you can see it's opened let's say we added hydrogen to clothing you know that that that reaction is very is very it's very loud it's it reacts very low very rapid so let's say we react H+ in An open system matter can be exchanged in a way that is bubbling the liquid cannot spill out. So when the liquid spills out when liquid spills out matter has been exchanged and energy can also be exchanged because it can release it as a form of energy and energy can be exchanged like that. So you can see that the liquid spilling out is matter. Water is matter and heat coming out is also energy. So matter energy can be exchanged in an open system.

[00:06:31]When we talk about when I talk about a closed system, let's say this is a closed system action going on in it. The same reaction going on in it. If you also have hydrogen and al rapid reaction but because it's a closed system, the liquid cannot come out. That's matter. So matter cannot be exchanged because even if this is the has a closed a closed part so it won't come out. So matter cannot be exchanged but heat is energy. So heat can be exchanged because when this when this container is hot and you touch it you are going to feel hot. That mean you've exchanged the heat you've interacted with heat and you've conducted the heat. So heat has already exchanged. So in a closed system matter cannot be exchanged but it can be exchanged. But now let's talk about an isolated system. Now an isolated system we want to stop matter both matter and energy from getting out. So what we do is we pass the system.

[00:07:49]So we've covered the system. We've covered the system but we also want we don't want energy to be exchanged like in thermal flask. We don't want energy to be exchanged. to prevent energy heat energy to be exchanged at all cost. So we pack the system. So in an isolated system both matter and energy cannot be exchanged.

[00:08:12]What we call homogeneous and heterogeneous system. Homogeneous system from the from the name homogeneous it means it has just one phase. It exist in one phase. So that system just have the system is in one phase. Maybe we have two liquid mix together to give one liquid. Let's see in the system all we have is just liquid or all we have is just solid or all we have is just gas only exist in one phase. So even if you have two liquids want to add two liquids the liquids must be missible and it must be able to mix together to give just one liquid. In homogeneous in homogeneous system it must exist in only one ph. But in heterogeneous system it exist in different phases and you can have both liquid and solid in that system just like mixing sand and water. That's an hogenous system because sand is solid and water is liquid. So mixing sand and water is heterogeneous system. So those are the difference between homogeneous system and system properties in you have two different kind of properties. You need to know about you need to know about intensive properties and extensive properties. You need to know the meaning and the types of property. Examples of intensive and extensive properties.

[00:09:34]Number one we have the intensive properties.

[00:09:42]properties.

[00:09:50]So what we mean by intensive properties?

[00:09:52]These properties don't depend on mass.

[00:09:55]So let's say we have let's say we have this marker now and the density of this marker is 2 kg per me cube. Let's say the density of this matter is 2 kg cube. When I divide this mark into two, when I divide this mark into two, if I look for the density of this half is also going to be 2.5 km kg per me cube and this one is also going to be 2.5 kg per me cube. Irrespective of how small or how big it is as far as the same marker, it's going to have the same density. And that's what that's what happens to our to water.

[00:10:33]The amount of water present in your cup is 1 kg per me cube. The one in the ocean is also have the same density. So maybe is a Pacific is in the Pacific Ocean or the one at the back of your house or the one in your cup, the one you are drinking, everything has the same density and that's what intensive property. So density is an intensive property because it doesn't depend on mass. No matter how big or small the object you're considering, it always has that property. I also call this intensive property qualitative properties and extensive is called quantitative because those one depends on mass. So example of intensive properties are density, refractive index, specific heat capacity, no boiling point, melting point and so on.

[00:11:22]So from a the definition of intensive properties you know that of extensive properties are as properties that depend on mass just like its capacity it capacity dep depends on mass like mass also depends on mass and so on like that. So you should know the difference between intensive and extensive property. You should also know that internal energy is extensive property not intensive property. Internal energy is extensive properties. Enthalpy entropy is also extensive properties.

[00:11:59]Let's talk about let's talk about processes thermodynamic process that we have. So there are some thermodynamics processes that we have that you should be familiar with.

[00:12:11]The first one I'm going to be explaining is the isothermal process.

[00:12:17]Isothermal process number one that's process is from the word from the word thermal you should know we talking about it can you see my hand from the word you know we talking about it and heat or temperature so this ISO here means constant so ISO means constant temperature so isothermal process are process with constant temperature so So that's the the the key point you should note about isothermal processes. They have constant temperature. So you can say dt is z.

[00:12:57]This d means change but dt or change in t or change in c dt or change in t is equal to z. This is not over d or change in t is z. So that's isothermal constant temperature. And when I say something the change will be zero. So the second you need to know is isobaric barometer to measure temperature to measure pressure. So iso that's constant pressure I'm just giving you the the key word you need to know to remember the meaning parameter measurement pressure so iso means constant so that's constant pressure so in isobaric processes we have constant pressure as change in pressure is zero we also have isocoric also call this isocoric or call it iso to volutric from volutric isoric or isoltric means volume. So constant from dv is z. So in an isocoric process dv is z. We also have adabatic process. So this adabatic process there process that does not involve the exchange of energy. So adabatic process if you consider adabatic system energy does not enter a system and energy does not leave. It's just like an isolated system. Yes. So adabatic process in adabatic process changing change in quantity quantity of heat or quantity of energy is zero. You should know that when I mean changing changing changing all this change in zero if they ask you what is the temperature you don't say the temperature is zero the temperature is constant like in isal is process the temperature is constant the change in temperature is zero isobaric pressure is constant change in pressure zero is volume is constant change in volume zabatic the quantity of energy energy is constant change in energy is zero So note that the fifth process you should also know about is the cyclic process. When we talk about cyclic process these are processes. All right.

[00:15:23]So when when a reaction starts from a particular place when it starts from a particular reaction start from a particular place it goes through different processes and comes back to that exact place is called a cyclic process.

[00:15:40]Yes. And you should also know that in a cyclic process change in internal is also zero. So in cyclic process in cyclic process in cyclic process the change in internal energy is also zero.

[00:16:00]In adabatic change energy is also zero.

[00:16:03]This energy point of quantity of energy.

[00:16:09]So what other thing you need to know what I what you need to know the meaning of part function and state function.

[00:16:18]So from the word part from the word part it means these stuffs they follow parts they follow a way they follow a part they follow a way. So pass function are functions that they are change depend on the path followed. They don't depend on the initial and final state. They depend on the part for and the only part function that we have is work. Why state function they independent of the part for but they just depend on the final state and the initial state. So when you have volume now pressure volume temperature they're state functions part functions work. So let's talk about pressure now let's say pressure is state function you can have change in pressure and change in pressure is change in pressure is P2 minus P1 that's change in pressure that's change in pressure change in volume 2 is final P1 initial. So that's how you say state function they depend on final and initial state volume V2 minus V1 as you can see this is also temperature T2 minus T1 they depend on the final and initial but if is work you can never say work work is W2US W1 it doesn't it doesn't work like that it doesn't depend on the final initial state you need to calculate the path followed. So let's say you have like this. It's just like in physics 103 what I now and stuff is like this this volume work. So you need to you need to like solve it as PD but you cannot just use this formula. I need to solve it using the information given on this graph. So when it's expanding that does expansion in pressure let's say the pressure here is 500 and the volume here is 200. So the work will just be area of the graph.

[00:18:34]So it depends on the part followed. So that's why work is a part function.

[00:18:42]So the other way to explain thermal energy is is by saying it is the amount of kinetic energy of a unit substance and temperature is the the measure of that the measure of the average kinetic energy. That's how to to explain it another way to explain another way. You should also know the the degree of movement the degree of freedom or degree of movement of the three faces of matter.

[00:19:13]Solid, solid, liquid and gas.

[00:19:20]These are the three faces of matter. You should know this.

[00:19:24]So solid they have the rotational rotational freedom can rotate and vibrational vibrational motion vibrational motion. So rotational and vibrational for liquid it has both it has translational translational rotational rotational and vibrational.

[00:19:55]So for for solid just rotational vibrational for liquid both translational rotational and vibrational. Why for gas? It also has translational, rotational and vibrational just that the degree of movement of gas is very high like is even the highest compared to both liquid and solid.

[00:20:17]So note that solid does not have translational motion and the particle does the particle does not translate just rotates and vibrates in a fixed position while liquid has or gas or gas in more degree and they translate higher they vibrate more and they rotate more.