By Tasneem Ahmed

INTRODUCTION

Chemistry

• A Branch of science which deals with the structure, properties constituents and change which takes place is known as chemistry.

• Origin of chemistry -: Chemes means black in colour. Egyptian called black earth as “chemo ” and an early age the study of chemical science was known as chemistry.

• Antoine Lavoisier (1743, 1794) is known as the father of Modern Chemistry

NOTHING IS LOST, NOTHING IS CREATED, EVERYTHING IS TRANSFORMED

What Is Physical Chemistry?

If we look around us, chemical reactions are taking place everywhere.

When we strike a match to light our grills, a a chemical reaction occurs.
If we mix milk with baking powder in our favourite recipe, a reaction happens.
Why do some reactions create heat?
How is it that certain reactions proceed fast while others move very slow?
All these questions and more can be solved within the field of physical chemistry.
The term "physical chemistry" was coined by Mikhail Lomonosov in 1752, according to him

PHYSICAL CHEMISTRY

• The term "physical chemistry" was coined by Mikhail Lomonosov in 1752

• Physical Chemistry is the branch of chemistry dealing with the principles and methodologies of both chemistry and physics and is the study of how chemical structure impacts the physical properties of a substance. Physical chemistry gives us information that how light behaves like a particle in the form of Quantum. it also tells us that what sort of order of reaction a molecule possesses?

• it shows how ripening of fruits takes place and what phenomenon is going on and how photons are get converted into mass. how energy is produced from different resources and can be used for the benefits of humankind.

• Physical Chemistry includes the study of the physical properties of many different types of substances and on different scales (levels of physical detail).

• That is, it includes the study of the following scales of chemical properties of materials:

Macroscopic:
Macroscopic properties of substances describe how relatively massive quantities of the substance behave as a group,

• Example; melting points and boiling points, thermal conductivity, specific heat capacity

Microscopic:
Microscopic properties of substances concern details of their physical properties observable only using the magnification provided by microscopes

• Example; the shapes and structures of crystals

Major Branches of Chemistry

Ø Physical Chemistry

Ø Analytical Chemistry

Ø Biochemistry Chemistry

Ø Organic Chemistry

Ø Inorganic chemistry

SUB-BRANCHES OF PHYSICAL CHEMISTRY INCLUDE

Ø Electrochemistry (the study of the interaction of atoms, molecules, ions, and electric current)

Ø Photochemistry (the study of the chemical effects of light; photochemical reactions)

Ø Surface chemistry (the study of chemical reactions at interfaces)

Ø Chemical Kinetics (the study of rates of chemical reactions)

Ø Thermodynamics/Thermochemistry (the study of how heat relates to chemical change)

Ø Quantum Mechanics/Quantum Chemistry (the study of quantum mechanics and how it relates to chemical phenomena)

Ø Spectroscopy (the study of spectra of light or radiation)

Thermodynamics/Thermochemistry

The word ‘thermodynamics’ comes from the two Greek words

Ø ‘dynamic’ comes from the Greek word dunamikos, which means movement

Ø thermo means energy or temperature i.e. ‘thermometer,’

“The branch of science that deals with energy levels and the transfer of energy between systems and between different states of matter”

Thermodynamics is the scientific study of work, heat, and the related properties of chemical and mechanical systems.

Thermodynamic System

An an important concept in thermodynamics is the thermodynamic system. A thermodynamic system is one that interacts and exchanges energy with the area around it (transformation of energy). A system could be as simple as a block of metal or as complex as a compartment fire. Outside the system are its surroundings. The system and its surroundings comprise the universe.

Universe

Systems:

Ø A region of the universe that we direct our attention to

Ø part of the world has a special interest

Ø quantity of matter

Surroundings:

Ø Everything outside a system is called surroundings

Ø where we make us observation

Ø Everything other than the system

Boundary:

Ø The boundary or wall separates a system from its surroundings.

Ø imaginary or a physical thing that separate system and surrounding

ENERGY TRANSFER IS STUDIED IN THREE TYPES OF SYSTEMS:

Open systems

Open systems can exchange both matter and energy with an outside system. They are portions of larger systems and in intimate contact with the larger system. Your body is an open system.

Closed systems

Closed systems exchange energy but not matter with an outside system. Though they are typically portions of larger systems, they are not in complete contact. The Earth is essentially a closed system; it obtains lots of energy from the Sun but the exchange of matter with the outside is almost zero.

Isolated systems

Isolated systems can exchange neither energy nor matter with an outside system. While they may be portions of larger systems, they do not communicate with the outside in any way. The physical universe is an isolated system; a closed thermos bottle is essentially an isolated system (though its insulation is not perfect).

Heat can be transferred between open systems and between closed systems, but not between

isolated systems.

LAWS OF THERMODYNAMIC

The Zeroth Law

If two thermodynamic systems are each in thermal equilibrium with a third, then they are in thermal equilibrium with each other.

Two systems that are each found to be in thermal equilibrium with a third system will be found to be in thermal equilibrium with each other.

• The Zeroth law is so named as it came after the other 3. Laws 1, 2, and 3 had been around for a while before the importance of this law had been fully understood. It turned out that this law was so important and fundamental that it had to go before the other 3, and instead of renaming the already well known 3 laws they called the new one the Zeroth law and stuck it at the front of the list.

• it gives you information about mass/energy.

• I assume the water bucket in which you put a cup of tea … so if the water is in thermal equilibrium with tea. And tea is in thermal equilibrium with surrounding then you have to say water is in equilibrium with surrounding. That is what zeroth law is

• If A=B and C=B, then A=C. This may seem so obvious that is do not need stating but without this law, we could not define temperature and we couldn’t build thermometers.

First law of thermodynamics

• Energy can neither be created nor destroyed. It can only change forms. In any process, the total energy of the universe stays the same. For a thermodynamic cycle, the net heat supplied to the system equals the network done by the system.

• The first law of thermodynamics states that energy is conserved; it can neither be created nor destroyed, just changed from one for to another,

• “The total amount of energy in an isolated system is conserved.”

• it is simply saying that energy is conserved. You neither create energy nor destroy energy.

• The energy in a system can be converted to heat or work or other things, but you always have the same total that you started with.

• As an analogy, think of energy as indestructible blocks. If you have 30 blocks, then whatever you do to or with the blocks you will always have 30 of them at the end. You cannot destroy them, only move them around or divide them up, but there will always be 30. Sometimes you may lose one or more, but they still must be taken account of because Energy is Conserved.

Second law of thermodynamics

The entropy of an isolated system not in equilibrium will tend to increase over time, approaching a maximum value at equilibrium

There is no such device which develops 100% work. Nothing is in the world which convert energy one form to another form with no such losses. There must be some losses. And that is why no one is 100% efficient.

Entropy and enthalpy

Both entropy and enthalpy are thermodynamically properties of a system.
Entropy is a measure of disorder or randomness of a system. An ordered system has low entropy. A disordered system has high entropy.

Enthalpy is defined as the sum of internal energy of a system and the product of the pressure and volume of the system. The change in enthalpy is the sum of the change in the internal energy and the work is done.
Enthalpy and entropy are different quantities. Enthalpy has the units of heat, joules. Entropy has the units of heat divided by temperature, joules per kelvin.

Third Law of Thermodynamics

As temperature approaches absolute zero, the entropy of a system approaches a constant minimum.

• This is the most famous (among scientists at least) and important laws of all science. It states;

“The the entropy of the universe tends to a maximum.”

• In other words, Entropy either stays the same or gets bigger, the entropy of the universe can never go down. There is no such device which has zero entropy. The third law provides an absolute reference point for measuring entropy, saying that

“As the temperature of a system approaches absolute zero (−273.15°C, 0 K), then the value of the entropy approaches a minimum.”

• The value of the entropy is usually 0 at 0K, however there are some cases where there is still a small amount of residual entropy in the system.