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Physical Chemistry


Physical chemistry can be described as a set of  quantitative approach to the study of chemical problems. The principles of physical chemistry can be applied to the study of any chemical system.

Physical Chemistry is the application of physical principles and measurements to understand the properties of matter.
Physical Chemistry is the study of fundamental physical changes that control the properties and behavior of chemical reactions. In short, the science that uses theories and practices from physics to study chemical systems is called Physical Chemistry.

What is Physical Chemistry?

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Physical chemistry involves both the study of physics and chemistry. Physics has been defined as the study of the properties of matter that are shared by all substances. On the other hand, Chemistry involves the study of properties of individual substances. Physical Chemistry includes study of the physical properties of many different types of substances and on different scales. Physical Chemistry involves theories, measurements, and techniques in physics to understand and explain chemical substances.

Example: The thermodynamic analysis of macroscopic chemical phenomena

Physical chemistry is the study of atomic, subatomic, macroscopic and particulate phenomena applying the principles, practices and concepts of physics such as energy, force, motion, thermodynamics, quantum chemistry, statistical mechanics and dynamics, equilibrium in chemical systems in terms of laws and concepts of physics for the development of new technologies for the environment, energy and medicine.
Physical chemistry is the branch of chemistry that deals with the physical structure of chemical compounds, the way they react with other matter and the bonds that hold their atoms together.

Behavior of Gases and Liquids

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The simplest state of matter is a gas, a form of matter that fills any container it occupies. Solids, liquids and gases are all made up of atoms, molecules and ions, but the behaviors of these particles differ in the three phases.

Liquids and solids are often referred to as condensed phases because the particles are very close together. Gas can dissolve in liquids one example is a soft drink, which has carbon dioxide gas dissolved in water.

Similarly is the ocean where the solubility of oxygen is essential to fish and other animal life and solubility of carbon dioxide is important for algae and other plant life.

Solid Substances and their Mixtures

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In chemistry a solution is actually a type of mixture. Salt water is a “Homogeneous mixture alternatively sand in water is a “Heterogeneous mixture”. Solids can be hard like a rock, soft like fur, big like an asteroid, or small like grains of sand.
Solids hold their shape and they don't flow like a liquid. Solids can hold their shape because their molecules are tightly packed together. Dissolution of a solid substance is one of the heterogeneous processes occurring on the boundary between two phases. Solids can have pure elements or a variety of compounds inside they can be made of anything. When you have a solid with more than one type of compound, it is called a mixture. Concrete is a good example of a man-made solid mixture.

The Fundamentals of Chemical Thermodynamics

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Thermodynamics is concerned with the equations and variables of state, energy exchanged at physio-chemical processes and chemical equilibrium. Thermodynamics, systems are classified according to their ability to exchange matter and/or energy with their environment. Chemical thermodynamics is the study of the interrelation of heat and work with chemical reactions or with physical changes of state within the limits of the laws of thermodynamics. It is the study of the role of energy in a chemical change and in determining the behavior of materials. 
We can apply the laws on physical and chemical process and can determine the energy change through 1st, 2nd or zeroth laws of thermodynamics:

The Zeroth Law of Thermodynamics: states that if two systems are in thermodynamic equilibrium with a third system, the two original systems are in thermal equilibrium with each other.

First law of Thermodynamics:
 also known as the Law of Conservation of energy states that, energy can never be created or destroyed; it can only be transferred as heat or work or from one form to another. Energy can take variety of forms, for example kinetic energy, thermal energy or chemical energy. These different forms of energy can transform one to another however the sum total of all types of energy must remain constant.

Enthalpy: Sum of all kinds of energy such as kinetic, vibrational, rotational energy of molecules, energy of chemical bonds, etc. being present in a thermodynamic system or absorbed by a chemical reaction at constant pressure. We use the symbol 'ΔH' to indicate enthalpy.

Second law of Thermodynamics: there is an inherent direction in which any system not at equilibrium moves. When a spontaneous event in our universe occurs, the total entropy of the universe increases. Example – falling of an object, rusting of shiny nail in humid air.

Entropy: a thermodynamic quantity representing the amount of energy in a system that is no longer available for doing mechanical work. The dispersal of energy and matter is described by the thermodynamic state function entropy. We use the symbol 'ΔS' to indicate entropy. The greater the dispersal of energy or matter in a system, the higher is its entropy.

Third Law of Thermodynamics:  states that the entropy of a system approaches a constant value as the temperature approaches zero.

Phase Equilibrium and Chemical Equilibrium

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Phase Equilibrium: is the equality where C is the number of components and P is the number of phases in thermodynamic equilibrium with each other. Phase equilibrium occurs when two different thermodynamic phases of an element are in equilibrium with each other.

The precise temperature point when an element changes its phase from to a solid, liquid, or gas, there is a balance between the two phases and they are in equilibrium. Any change in Temperature and Pressure causes an increase in energy from Equilibrium thus forcing a move to another ‘state.’

Example: Take some boiling water and pour it into a glass container, and close it tight. As the water cools, condensation takes place, and water vapor will condense on the sides of the container.

Chemical Equilibrium: is the state in which both reactants and products are present in concentrations which have no further tendency to change with time. Chemical equilibrium may also be called a "steady state reaction." In chemical equilibrium, substances form and break down at the same rate, and the number of molecules of each substance becomes certain and constant.