7.002- Definations in Thermodynamics


System – The part of universe which we are studying about.

  1. Open : Mass and Energy can transfer between the System and the Surroundings
  2. Closed : Energy can transfer between the System and the Surroundings, but NOT MASS.
  3. Isolated : – Neither Mass nor Energy can transfer between the System and the Surroundings

Surrounding – rest of universe is surrounding (anything except system)

Boundary- The line that divide the system and surrounding.7-002-2

 Describing systems requires:

  • A few macroscopic properties: p, T, V, n, m…
  • Knowledge of System if it is Homogeneous or Heterogeneous
  • Knowledge of System if it is Equilibrium State
  • Knowledge of the number of components

Condition on applicability of Thermodynamics –

The laws of thermodynamics are always applicable but for practical problem but we are going to apply them only when the system are in equilibrium,  that is, the observation I have now should be the same 1 min, 1 hour,1 decade from now for the system i.e. results are time independent.

Now here it is important that we don’t confuse during a process, say I pulled or pushed a piston, and I’m doing a analysis of some factors so, The principle or equations we are going to discuss in this course, are not going to work if the effect of the action is not given enough time to come in equilibrium.In the same condition Say all the value are constant after five minute, and will not change until I don’t change something in or out of the system, This is the equilibrium state and our calculation will take and give these values only.

 There are two classes divided for the properties-

  • Extensive – the properties which are dependent on the quantity

Example – volume, mass, moles etc

  • Intensive – the properties which are independent of the quantity

Example – Temperature, Molecular weight etc

Now there is some terminology which makes an intensive property from extensive one like

Molar volume- like volume is extensive but molar volume is intensive because it is defined for a mole and don’t actually mind what quantity is present in solution.

Now the thing comes how to distinguish. Very simple, Cut it into half (system), if entity changes then the entity is extensive else intensive

Memory tip– most of times we remember the way to find be confuse with the term so just remember intensive by independent.

State Variable – Define the state of equilibrium

State variable are independent of path taken to achieve from state 1 to state 2.These properties are something that is going to be base of problem solving and much more interesting fact.For knowing everything there is for a system of a single component and single phase. We need number moles of component and any two variables from (P, V, and T).

 Notation of Equilibrium state

E.g ,     2    Cl2     (    g, 4bar, 4000C)

No. Of moles- Substance –phase -pressure– Temperature7-002-1

There are multiple paths for single state change Path 1, path 2, path 3. The properties at state 1 and The state function has a good thing like no matter we take State 2 will remain as it is in all possible paths reaching by any possible path we can take.

Different types of processes in thermodynamics

Adiabatic –No heat exchange between the system and surrounding at any time.

Isobaric – The pressure remain constant throughout the process

Isotherm- The temperature remains constant throughout the process

So, now that we know the language of thermodynamics, from next lecture onward, we will see the traditional problems, some practical situations and a lot of analysis of thermodynamic processes and there real life application in our very own scientific way.

Abhishek kumar jha

(Chemistry at Utkarshini)




Lecture notes –7-001-introduction-tothermodynamics in continuation to first

Video link – https://www.youtube.com/watch?v=pMfyg2nJfoo


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