Chemical Thermodynamics - SS2 Chemistry Past Questions and Answers - page 1

The laws of thermodynamics are fundamental principles that govern the behaviour and transformations of energy in physical and chemical systems. The three laws of thermodynamics are as follows:

1.    First Law of Thermodynamics (Law of Energy Conservation): The first law states that energy cannot be created or destroyed in an isolated system. It can only change form or be transferred from one system to another. This law is also known as the law of energy conservation. Mathematically, it can be expressed as ΔU = Q - W, where ΔU is the change in internal energy of the system, Q is the heat added to the system, and W is the work done on the system.

Example: When a gas is compressed in a cylinder, work is done on the gas by the surroundings, and the internal energy of the gas increases. If heat is added to the system, the internal energy further increases, and if work is done by the system, the internal energy decreases.

2.    Second Law of Thermodynamics (Law of Entropy): The second law of thermodynamics states that the entropy (a measure of the disorder or randomness) of an isolated system always increases or remains constant in a spontaneous process. This law implies that natural processes tend to move towards a state of greater disorder. It also introduces the concept of entropy as a measure of the system's energy dispersal or the number of microstates associated with a given macrostate.

Example: Heat spontaneously flows from a hot object to a cold object, resulting in an increase in the overall entropy of the system. A cup of hot coffee left in a room eventually cools down as heat is transferred to the surroundings.