# Entropy and feasibility of reactions

## Entropy and feasibility of reactions

## Understanding Entropy

**Entropy (S)**is a measure of the**disorder**or randomness of a system.- In any system, there is a natural tendency for the entropy to increase.
- The unit for entropy is
**joules per mole per kelvin (J mol⁻¹ K⁻¹)**.

## Entropy and Physical States

**Gases**have the highest entropy because their particles can move freely and randomly.**Solids**have the lowest entropy as their particles are fixed in place.**Liquids**have an intermediate entropy value as their particles have some freedom of movement.- The entropy of a system usually
**increases during a chemical reaction**. This is due to the conversion of reactants into products, often forming gaseous products from solid or liquid reactants.

## Calculating Entropy Change

- The
**total entropy change**for a reaction (∆Stotal) can be calculated by adding the entropy change of the environment (∆Ssurroundings) and the entropy change of the system (∆Ssystem). - ∆Ssystem can be calculated using the equation: ∆Ssystem = ΣSproducts - ΣSreactants
- ∆Ssurroundings can be calculated from the enthalpy change of the reaction (∆H) and the temperature in kelvin (T), using the equation: ∆Ssurroundings = -∆H / T

## Entropy and the Feasibility of Reactions

- A reaction is feasible if the total entropy change for a reaction (∆Stotal) is positive, which implies the
**overall disorder of the universe increases**due to the reaction. - If ∆G (Gibbs free energy) of a reaction is negative, the reaction is spontaneous and feasible under constant temperature and pressure. ∆G can be calculated from the equation: ∆G = ∆H - T∆Ssystem
- However, a positive ∆Stotal does not guarantee a reaction will occur. Other factors such as
**kinetic barriers**(e.g., activation energy) may prevent a feasible reaction from occurring.

## Examples of Entropy Changes in Reactions

- For
**endothermic reactions**, the heat absorbed from the surroundings increases the entropy of the system, contributing to a positive ∆Stotal. **Dissolving a solid**in a solvent usually results in an increase in entropy due to increased disorder.**Chemical reactions**that produce more moles of gas result in an increase in entropy.