Thermodynamics: Class 11 Chemistry NCERT Chapter 6

Key Features of NCERT Material for Class 11 Chemistry Chapter 6  – Thermodynamics

In the last chapter 5, you studied about states of matter. In this chapter: Thermodynamics, you will study about for what reason do you feel hotter when you rub your palms together in winter? This happens because scouring our palms produces heat. Additionally, in steam motors, we utilize the warmth of the steam for moving the cylinders, because of which the wheels of the train pivot. Be that as it may, what’s the whole procedure behind this? All things considered, this occurs because of ‘thermodynamics’. Let us concentrate more on it beneath. 

What does Thermodynamics mean? 

Let us just split the word thermodynamics into two words, thermo and elements. ‘Thermo’ represents heat while ‘elements’ are utilized regarding a mechanical movement, which includes ‘work.’ Accordingly, Thermodynamics is the part of material science that manages the connection between heat and different types of energy. 

Presently which amounts decide the condition of the system? They are pressure, volume, temperature, mass or piece, inner energy, and so forth. These amounts are alluded to as the state factors and estimated just when the system is at balance. The systems that we concentrate on thermodynamics comprise enormous quantities of iotas or atoms communicating in convoluted manners. Yet, in the event that these systems meet the correct balance, they can be portrayed with an exceptionally modest number of estimations or figures. 

Quick Revision notes 

  • Important Terms and Definitions 

System: Refers to the segment of the universe, which is under perception. 

Environmental factors: Everything else known to man with the exception of the system is called environmental factors. Think of the universe as, Universe = System + Surroundings. 

Open System: In a system, when there’s an exchange of energy and matter occurring with the environmental factors, at that point, it is called an open system. 

For Example, the Presence of reactants in an open measuring utensil is a case of an open system. Shut System: A system is supposed to be a shut system when there is no trade of matter,’ yet trade of energy is conceivable. 

For instance: The nearness of reactants in a shut vessel made of directing material. 

Isolated System: In a system, when no trade of energy or matter happens with the environmental factors, it is called an isolated system. 

For instance: The nearness of reactants in a thermos flask or substance in a protected shut vessel.

For Example, The reactants in a thermos flask, or substance in an insulated closed vessel is an example of the same.

Homogeneous System: A system is known as homogeneous when all the constituents present are in the same phase and are uniform all through the system. 

For Example, A-blend of two miscible liquids. 

Heterogeneous system: A blend is said to be heterogeneous when it consists of at least two phases, and the composition is not uniform. 

For Example, A blend of solid, which is not soluble in water.  

The state of the system: It refers to its macroscopic or mass properties which can be calculated by variables written below: 

volume (V), Pressure (P), temperature (T) and amount (n), and so forth. 

They are also known as state functions.

Isothermal process: When the operation is done at a constant temperature, it is said to be isothermal. For the isothermal process, dT = 0 Where dT is the adjustment in temperature.

Adiabatic process: It is a process wherein no transfer of heat among systems and surroundings takes place.

Isobaric process: When the process is done at constant pressure, it is said to be isobaric. for example dP = 0

Isochoric process: A process when it is carried out at constant volume, it is known as isochoric in nature. 

Cyclic process: If a system goes through a series of changes that lastly returns to its initial state, it is said to be a cyclic process.

Reversible Process: When during a process, a change is gotten such a way that the process could, at any second, be reversed by an infinitesimal change. The change is called reversible. 

  • Internal Energy: It is the total sum of the considerable number of forms of energy that a system can possess. 

In thermodynamics, it may change, if  

—- Matter enters or leaves the system

—-Matter enters or leaves the system

—- Heat passes into or out of the system 

Change in Internal Energy by Doing Work

Let us acquire the change in internal energy by accomplishing work. Let the initial state of the system be Temp. TA Internal energy = uA 

On doing some mechanical work, the new state is called state B and the Temp. TB. It is seen as 

TB > TA 

uB is the internal energy 

∴ uB – uA = Δu 

Change in Internal Energy through Transfer of Heat

It changes by transferring heat from the surroundings to the system without doing any work. 

Δu = q 

Where q is the heat absorbed by the system. It very well may be measured in terms of temperature distinction. 

q is +ve when the heat is transferred from the surrounding

s to the system. q is – ve when the heat is transferred from system to surroundings. At the point when the change of state is done both by accomplishing work and transfer of heat. 

Δu = q + w 

  • Work (Pressure-volume Work)

Let us consider a chamber with one mole of an ideal gas having a frictionless piston fitted in.

  • Work Done in Isothermal and Reversible Expansion of Ideal Gas

  • Isothermal and Free Expansion of an Ideal Gas

For isothermal expansion of an ideal gas into vacuum W = 0

  • Enthalpy (H)

It is characterized as an all-out heat substance of the system. It is equivalent to the sum of internal energy and pressure-volume work. 

Scientifically, H = U + PV

Change in enthalpy: At a constant pressure, Change in enthalpy is the heat developed by the system or absorbed.

ΔH = qp 

For exothermic reaction where System loses energy to Surroundings), 

ΔH and qp both are – Ve. 

For endothermic reaction where System absorbs energy from the Surroundings). 

ΔH and qp both are +Ve. 

Relation between ΔH and Δu.

  • Extensive property

An extensive property is a property whose worth depends on the amount or size of matter present in the system. 

For Example, Mass, volume, enthalpy, and so on are known as extensive property. 

  • Intensive property

Intensive properties don’t rely on the size of the matter or amount of the matter present in the system. For Example, temperature, density, pressure, and so forth are called intensive properties.

  • Heat capacity

The increase in temperature is relative to the heat transferred. 

q = coeff. x ΔT 

q = CΔT 

Where coefficient C is called the heat limit. 

C is straightforwardly corresponding to the amount of substance. 

Cm = C/n 

It is the heat limit concerning 1 mole of the substance. 

  • Molar heat capacity

It is characterized as the amount of heat required to raise the temperature of a substance by 1° (Kelvin or Celsius). 

  • Specific Heat Capacity

It is described as the heat needed to increase one unit mass’s temperature by 1° (Kelvin or Celsius). 

C x m x ΔT = q

where ΔT = rise in temperature and m = mass  

  • Relation Between Cv and Cvp for an Ideal Gas

heat limit at const volume = Cv 

 heat limit at const pressure = Cp 

qv, at constant volume = CvΔT = ΔU 

 qp, at constant pressure = Cp ΔT = ΔH 

For ideal gas of one mole 

 ΔU + Δ (PV) = ΔU + Δ (RT) =ΔH 

 ΔU + RΔT =ΔH 

On finding the values of ΔH and Δu, the condition is changed as 

Cp ΔT = CvΔT + RΔT 

or on the other hand R = Cp-Cv

  • Measurement of ΔH—Calorimetry ΔU and 

Determination of ΔU: ΔU is calculated in a special sort of calorimeter, called bomb calorimeter

Working with a calorimeter.The calorimeter comprises of a strong vessel called (bomb), which can take high pressure. It is surrounded by a water shower to ensure that no heat is lost to the surroundings. 

Technique: A realized mass of the combustible substance is singed in the pressure of unadulterated dioxygen in the steel bomb. Heat advanced during the reaction is transferred to the water, and its temperature is checked. 

  • Enthalpy Changes During Phase Transformation

Enthalpy of fusion:It is is the change in enthalpy or heat energy when one mole of a solid at its liquefying point is changed over into liquid state. 

Enthalpy of vaporization: It is characterized as the heat energy or change in enthalpy when one mole of a liquid at its direct boiling changes toward a gaseous state. 

Enthalpy of Sublimation:  Enthalpy of sublimation is characterized as the adjustment in the heat energy or change in enthalpy when one mole of solid straightforwardly changes into a gaseous state at a temperature beneath its dissolving point. 

  • Standard Enthalpy of Formation

Enthalpy of formation is characterized as the adjustment in enthalpy in the formation of 1 mole of a substance from its constituting elements under standard temperature conditions at 298K and 1 atm pressure. 

Enthalpy of Combustion:  Enthalpy of formation is characterized as the adjustment in enthalpy in the formation of 1 mole of a substance from its constituting elements under standard temperature conditions at 298K and 1 atm pressure. 

  • Thermochemical Equation

A reasonable chemical condition, along with the estimation of ΔrH and the physical state of reactants and products, is known as a thermochemical condition

Conventions regarding thermochemical equations

  1. The coefficients in a reasonable thermochemical condition allude to the number of moles of reactants and products associated with the reaction.   
  • Hess’s Law of Constant Heat Summation

The aggregate sum of heat advanced or absorbed in a reaction is the same as whether it takes place in one or several steps. 

  • Born-Haber Cycle

It is impractical to decide the Lattice enthalpy of an ionic compound by direct experiment. Thus, it very well may be determined by the following steps. The diagrams which show these steps are known as Born-Haber Cycle. 

  • Spontaneity

Spontaneous Process:    A process that can happen without anyone else or has a propensity to occur is called spontaneously. 

The spontaneous process need not be instantaneous. Its real speed can fluctuate from slow to very fast. 

A few examples of spontaneous process are:

(I) Common salt gets dissolved in water of its own. 

(ii) Carbon monoxide is oxidized to carbon dioxide of its own. 

  • Entropy (S)

Entropy is a measure of the level of randomness or disorder of a system. The entropy of a substance is least in the solid-state while it is most extreme in a gaseous state. 

The adjustment in entropy in a spontaneous process is expressed as ΔS.

  • Gibbs Energy and Spontaneity

Another thermodynamic capacity, the Gibbs energy or Gibbs work G, can be characterized as  H-TS=G 

 ΔH – TΔS=ΔG  

Gibbs energy change = enthalpy change – entropy changeΔG  * temperature gives a measure for spontaneity at constant temperature and pressure, (I) The process is spontaneous, If ΔG is negative (< 0) 

(ii) If ΔG is positive (> 0), the process is non-spontaneous, If ΔG is positive (> 0), 

  • Free Energy Change in Reversible Reaction 

Questions

Q.The temperature at the base of a high waterfall is higher than that at the top because 

  • without anyone else, the heat flows from higher to bring down the temperature. 
  • The distinction in tallness causes the distinction in pressure. 
  • Warm energy transforms into chemical energy. 
  • Mechanical energy transforms into warm energy. 

Answer: D 

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