Table of Contents
A Guide to Enthalpy and Entropy
Enthalpy is a measure of the internal energy of a system, while entropy is a measure of the disorder of a system. The two concepts are related by the second law of thermodynamics, which states that entropy always increases over time.
Enthalpy is a measure of the energy that is available to do work in a system. It is calculated by adding up the energy of the system’s particles. Entropy is a measure of the disorder of a system. It is calculated by counting the number of different ways that the system’s particles can be arranged.
The second law of thermodynamics states that entropy always increases over time. This law is due to the fact that entropy is a measure of the disorder of a system, and disorder always increases over time.
What is Enthalpy?
The enthalpy of a system is the heat content of the system. The enthalpy of a system is the sum of the internal energy of the system and the product of the pressure and the volume of the system.
Change in Enthalpy
The change in enthalpy is a measure of the heat energy transferred in a chemical reaction. It is calculated by subtracting the enthalpy of the products from the enthalpy of the reactants. Enthalpy is a measure of the internal energy of a system and is determined by the temperature and pressure of the system.
Standard Enthalpy Change
Standard enthalpy change (enthalpy of formation) is the enthalpy change that accompanies the formation of one mole of a substance from its constituent elements in their standard states. This value is usually given in kilojoules per mole (kJ/mol) or in kilocalories per mole (kcal/mol). The standard enthalpy change for the formation of a gas is zero, because the enthalpy of a gas is determined only by its temperature and pressure.
Standard Enthalpy Change of Formation
The standard enthalpy change of formation (ΔH f °) is the enthalpy change that occurs when 1 mole of a substance is formed from its elements in their standard states.
ΔH f ° =enthalpy change when 1 mole of a substance is formed from its elements in their standard states
Standard Enthalpy Change of Combustion
Standard Enthalpy Change of Combustion is the enthalpy change that occurs when 1 mole of a substance is completely burned in oxygen.
What is Entropy?
The entropy of a system is a measure of its disorder. The higher the entropy of a system, the more disorder there is in it.
Absolute Entropy
The absolute entropy of a system is the entropy of the system in its most disordered state.
Entropy Characteristics
The entropy of a system is a measure of its disorder. The higher the entropy of a system, the more disorder there is.
The entropy of a system can be increased by adding energy to the system, by adding new particles to the system, or by increasing the temperature of the system.
The entropy of a system can be decreased by removing energy from the system, by removing particles from the system, or by decreasing the temperature of the system.
Calculation of Entropy
The entropy of a system is a measure of its disorder. It is calculated by taking the natural log of the number of microstates that are possible for the system.
S = ln(W)
Enthalpy and Entropy Relation
The enthalpy and entropy of a system are related by the equation:
\[H = S + PV\]
Where:
H is the enthalpy
S is the entropy
P is the pressure
V is the volume
