Maharashtra Board Class 12 Chemistry Chapter 4 Chemical Thermodynamics PDF Download

4. Chemical Thermodynamics

4.1 Introduction

You know transformation of liquid water into vapour, solid ice into liquid water or burning of carbon forming carbon dioxide, \(\text{CO}_2\), are accompanied by a change in energy. In dry cell, the chemical energy is converted into electrical energy. On the other hand, in electroplating of metals electrical energy is converted into chemical energy. Thus it may be realized that the energy can be transformed from one form into another.

Can you recall?

1. How do you define energy?

2. What are the different forms of energy?

Do you know?

At the top of dam, water is stored in a reservoir. It has certain potential energy due to its height from ground level and its kinetic energy is negligible as it is not in motion. As the water starts to fall down through an outlet its potential energy decreases and kinetic energy increases due to the downward velocity. It means that potential energy of falling water is converted into kinetic energy.

Thermodynamics is concerned with the energy changes in physical and chemical transformations. Thermodynamics, however gives no information on the rates of physical or chemical processes or underlying mechanisms involved in these.

4.2 Terms used in thermodynamics

4.2.1 System and surrounding

Consider a gas enclosed in a cylinder equipped with a movable piston. Suppose we undertake study of change in volume of a gas and the amount of energy released or gained by a gas when the pressure is varied by putting certain mass on the piston. In this case, a gas under study is called the system.

A part of the universe under thermodynamic investigation is called the system. All other parts of the universe outside the system such as cylinder, room and others, are surroundings. The universe is made of system plus surroundings.

4.2.2 Types of system

Observe and discuss...

Observe the figure and discuss with reference to transaction of energy and matter.

Three types of systems are shown in the figure.

Teacher's Note

A system is like a small cup of tea in your hand. The cup is the system, and the room around it is the surroundings. Heat moves between them. In India, we use the example of a tiffin box to teach this. The food inside is the system, and everything outside is the surroundings.

Exam Trick

Remember the three types: Open system = cup without cover, Closed system = cup with cover, Isolated system = cup with cover and wrapped in cloth. Just think of a real Indian lunch box.

Points to Remember

Open system exchanges both energy and matter with surroundings.

Closed system exchanges only energy, not matter with surroundings.

Isolated system exchanges neither energy nor matter with surroundings.

System is what we study. Surroundings is everything else.

Together, system plus surroundings equals the universe.

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