Second Law of Thermodynamics

The application of First Law of Thermodynamics process led to the establishment of a new property named internal energy (U), the application of the second law to a process leads to the establishment of another new property names as entropy (S).

Entropy is defined as follows

Δ

S

=

Q

T

rev

For a reversible thermodynamic process between two states, from state 1 to state 2 in an open system, the change in entropy is given by

It is found by applying Clausius inequality that for for an irreversible process from state 1 to state 2, the change in entropy is given by

First Law of Thermodynamics

The First Law of Thermodynamics states that energy is neither created nor destroyed, thus the total energy of the universe is a constant. However, energy can certainly be transferred from one form to another form.

The 1st Law of thermodynamics is mathematically stated as follows:

§dQ = §dW

During a thermodynamic cycle, a cyclic process the systems undergoes, the cyclic integral of heat added is equal to integral of work done. the first law equation can also be written in the form,

§(dQ – dW) = 0

Equation dU = dQ - dW is corollary for first law of thermodynamics. It shows that there exists a property internal energy (U) of the system, such that a change in its value is equal to the difference in heat entering and work leaving the system.

Sign convention for heat and work in  first law of thermodynamics is represented in picture below.

Another property named enthalpy (H) can also be defined now as a combination of properties U, p and V.

H = U + pV

For a reversible process, since dW = pdV, the first law of thermodynamics can also be written as

dQ = dU + pdV

Temperature conversion from one scale to another scale

A temperature scale is established by assigning numerical values to certain reproducible states. It is customary to use the fixed points ice point and steam point.

Ice point is the equilibrium temperature of ice with air-saturated water at a pressure of 101.325 kPa which assigned a value of 0 degree centigrade.

Steam point is the equilibrium temperature of pure water with its own vapor at 101.325 kPa which is assigned a value of 100 deg C.

The temperature scale with the above fixed points is called Celsius scale.

Relationship between different temperature scales

Where,

LPF = Lower Fixed Point,

UPF = Upper Fixed Point.

F = Fahrenhiet scale,

C = Centigrade scale,
K = Kelvin scale

R = Reaumer’s scale,

ρ = Our defined scale,

Below I have given the program for converting temperature from one scale to another scale. Write the value of any one scale and then press 'Calculate' then you will get corresponding values in the remaining scales.

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Temperature Scale Converter

Fahrenheit Scale(F): 
Celsius Scale (C): 
Reaumer Scale (R): 
Kelvin Scale (K): 

    

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Gas Laws

Gas Laws explain the behavior of an ideal gas in terms of Temperature, Pressure, Volume. The following are some of the important gas laws are

• Boyle’s Law
• Charles Law
• Gay-Lussac’s Law
• Avogadro’s law
• Universal Gas Law

Boyle’s Law:

Boyle’s law states that the volume of a given mass of gas (V) is inversely proportional to its absolute pressure (P), provided the temperature of the gas (T) remains constant.
Boyle’s law formula

Charles Law:

According to Charles law, the volume of a given mass of gas (V) is directly proportional to its absolute temperature (T), when its pressure remains constant.
Charles law formula

Gay-Lussac’s Law:

Gay-Lussac's Law is also know as Amontons’ law. It states that if the volume of a given mass of a gas (V) is kept constant, then the pressure of the gas (P) is directly proportional to its absolute temperature (T).
Gay-Lussac's Law Formula

Avogadro’s Law:

Avogadro's law states that equal volumes of different perfect gases, at the same temperature (T) and pressure (P), contain equal number of molecules (n).
Avogadro’s law equation

Universal Gas Law:

Combined Gas law is derived from the three gas laws Boyles law, Charles law and Gay-Lussacs law.

Universal Gas Law Formula