Importance of prediction of thermodynamic properties

 PREDICTION OF THERMODYNAMIC PROPERTIES

       

 What are thermodynamic properties ?

            A quantity which is either an attribute of an entire system or is a function of position which is continuous and does not vary rapidly over microscopic distances, except possibly for abrupt changes at boundaries between phases of the system; examples are temperature, pressure, volume, concentration, surface tension, and viscosity. Also known as macroscopic property.

There are two main types of thermodynamic properties :-

Laws of Thermodynamics

1. Zeroth Law of Thermodynamic -

Suppose there are two systems A and B. An adiabatic wall separates the two. Each system A and B is in contact with a third system C, separated by a conducting wall as shown in fig 2.1a. The states of the systems will change and the systems A and B will eventually come to equilibrium with system C. After this, if the wall separating the Systems A and B is replaced by a conducting wall while the one separating the both of them from C is separated by an adiabatic wall (fig 2.1b), it is observed that there are no variations in the states of systems A and B. In other words they are in thermal equilibrium. This experiment is the basis of Zeroth Law of Thermodynamics. R. H. Fowler stated it as 'two systems in thermal equilibrium with a third system separately are in thermal equilibrium with each other.'

Figure 1: Zeroth law of thermodynamics

Importance of zeroth Law :

• Importance of zeroth law of thermodynamics .It tells about the state of thermal equilibrium of the system. 
• It defines the exchange of heat and also defines the temperature of the system.
• If we want to measure the accurate temperature, a reference body is required and a certain characteristic of that body which changes with temperature. 
• The change in that characteristic may be taken as an indication of a change of temperature. That selected characteristic is known as thermodynamic property.

2. First Law of Thermodynamic :

The first law of thermodynamics is a thermodynamic adaptation of the concept of conservation of energy, differentiating three types of energy transfer: heat, thermodynamic work, and energy associated with matter transfer, and linking these to an internal energy function of a body.

The law of conservation of energy asserts that the total energy of any isolated system (in which energy and matter cannot be transferred beyond the system border) is constant; energy can be changed from one form to another, but it cannot be created or destroyed.

Thus, the principle of conservation of energy then implies:

 𝚫Q = 𝚫U + 𝚫W

Figure 2 Energy conservation 

Importance of first law :

• It gives the relationship between heat and work.
• It is merely the law of conservation of energy generalized to include heat as a form of energy transfer.
• The energy of an isolated system remains constant.
• Heat and work are different forms of the same entity called energy.
• Heat and work are equivalent to each other.

3. Second Law of Thermodynamic :

The concept of entropy as a physical attribute of a thermodynamic system is established by the second law of thermodynamics. Despite following the necessity of energy conservation as specified in the first law of thermodynamics, entropy change predicts the direction of spontaneous processes and determines whether they are irreversible or impossible. The second law can be stated as follows: when isolated systems are left to spontaneous evolution, their entropy cannot fall because they always reach a state of thermodynamic equilibrium, where the entropy is highest at the given internal energy. The entropy of a system is constant if all operations are reversible. The irreversibility of natural processes is explained by a rise in entropy, which is commonly referred to as the arrow of time.

Importance of second law :

• Second law of thermodynamics is very important because it talks about entropy, ‘entropy dictates whether or not a process or a reaction is going to be spontaneous’.
• Any natural process happening around you is driven by entropy.

4. Third Law of Thermodynamic :

The third law of thermodynamics states as follows, regarding the properties of closed systems in thermodynamic equilibrium. The entropy of a system approaches a constant value as its temperature approaches absolute zero.

Importance of Third Law :

• It defines the sign of the entropy of any substance at temperatures above absolute zero as positive, and it provides a fixed reference point that allows us to measure the absolute entropy of any substance at any temperature.
• It helps to calculate the thermodynamic properties.
• It is helpful to measure the chemical affinity.
• It explains the behavior of the solids at very low temperature.
• It also helps to  analyze the chemical and phase equilibrium.

Thermodynamic properties 

1. Internal Energy :

The energy contained within a thermodynamic system is known as its internal energy. It's the amount of energy required to build or prepare a system in any given internal condition. It excludes the kinetic energy of the system's motion as a whole, as well as the potential energy of the system as a whole due to external force fields, which includes the energy of displacement of the system's surroundings. It keeps track of the system's energy gains and losses as a result of changes in its internal condition.

figure showing sign convection

The energy possessed by all of a system's constituents, notably atoms, ions, and molecules, is equal to the system's internal energy. The sum of the translational energy (Ut), vibrational energy (Uv), rotational energy (Ur), bond energy (Ub), electronic energy (Ue), and energy owing to molecular interactions is the total energy of all molecules in a system (Ui).

U = Ut + Uv + Ur+ Ub+ Ue+ Ui

Importance of internal energy :

• Internal energy is important for understanding phase changes, chemical reactions, nuclear reactions, and many other microscopic phenomena, as the possible energies between molecules and atoms are important. Both objects exhibit macroscopic and microscopic energy in vacuum.

2. Enthalpy

The sum of the system's internal energy and the product of its pressure and volume is the enthalpy of a thermodynamic system. It's a state function that's used in a variety of measurements in chemical, biological, and physical systems at constant pressure, which the large ambient atmosphere conveniently provides. The work required to establish the system's physical dimensions, i.e. to make room for it by displacing its surroundings, is expressed by the pressure–volume term. For solids and liquids under normal conditions, the pressure-volume term is very small, and for gases, it is fairly small. As a result, in chemical systems, enthalpy stands in for energy; bond, lattice, solvation, and other "energies" in chemistry are actually enthalpy differences. Enthalpy depends only on the final configuration of internal energy, pressure, and volume as a state function, not on the path taken to get there.

where U is internal energy and PV is the product of pressure and volume work done by system.

Importance of enthalpy :

• We can determine whether a reaction was endothermic (heat absorbed, positive change in enthalpy) or exothermic (heat released, negative change in enthalpy) by measuring the change in enthalpy (released heat, a negative change in enthalpy.)
• It's used to figure out how much heat a chemical reaction produces.
• In calorimetry, the change in enthalpy is used to measure heat flow.
• It is used to assess a throttling or Joule-Thomson expansion process.
• A compressor's minimum power is calculated using enthalpy.
• During a change in the state of matter, enthalpy changes.
• Enthalpy has numerous other applications in thermal engineering.

3. Gibbs Free Energy

Gibbs free energy, also known as Gibbs function, Gibbs energy, or free enthalpy, is a quantity used to measure the maximum amount of work done in a thermodynamic system when temperature and pressure remain constant. The symbol 'G' stands for Gibbs free energy. Its energy is typically measured in Joules or Kilojoules. The maximum amount of work that can be extracted from a closed system is defined as Gibbs free energy.

Josiah Willard Gibbs, an American scientist, discovered this property in 1876 while conducting experiments to predict the behavior of systems when they are combined or whether a process can occur simultaneously and spontaneously. "Available energy" was another name for Gibbs free energy. The Gibbs free energy (or Gibbs energy) is a thermodynamic potential that can be used to calculate the maximum reversible work that a thermodynamic system can perform at a constant temperature and pressure in thermodynamics.

Where delta H is change in enthalpy,

    and T is Temperature and S is entropy of the system

Importance of Gibbs free energy :

• ΔG°(standard) and ΔG_f° refer to single, specific chemical changes in which all components ( reactants and products ) are in their standard states.
• The physical meaning of ΔG is that it tells us how far the free energy of the system has changed from G° of the pure reactants.
• When ΔG reaches its minimum value, the composition of the system is at its equilibrium value.
• When $\Delta \text G$delta, start text, G, end text is negative, a process will proceed spontaneously and is referred to as exergonic.
• It tells the spontaneity of reaction  

4. Helmholtz free energy :

In thermodynamics, the Helmholtz free energy (or Helmholtz energy) is a thermodynamic potential that measures the useful work obtainable from a closed thermodynamic system at a constant temperature (isothermal). The change in the Helmholtz energy during a process is equal to the maximum amount of work that the system can perform in a thermodynamic process in which temperature is held constant. At constant temperature, the Helmholtz free energy is minimized at equilibrium.

where

F is the Helmholtz free energy  (SI: joules, CGS: ergs),

U is the internal energy of the system (SI: joules, CGS: ergs),

T is the absolute temperature (kelvins) of the surroundings, modelled as a heat bath,

S is the entropy of the system (SI: joules per kelvin, CGS: ergs per kelvin).

Importance :

• In explosives research Helmholtz free energy is often used, since explosive reactions by their nature induce pressure changes. It is also frequently used to define fundamental equations of state of pure substances.
• The Helmholtz free energy function for a pure substance (together with its partial derivatives) can be used to determine all other thermodynamic properties for the substance. 
• The second thermodynamic potential is the Helmholtz function, which is used to calculate work done in a closed system with constant temperature and volume. The other three thermodynamic potentials are internal energy, enthalpy, and Gibbs free energy.
• Many open systems exist in thermodynamics as the process of exchanging heat and work with respect to the environment, as opposed to closed systems. Biological systems that achieve an intrinsic reduction in entropy as they age are one of the most common examples.