Entropy

Entropy is a measure of disorder or randomness in a system.

• solid = lower entropy

• gas = higher entropy

Exothermic reaction gives out energy, while endothermic reactions absorbs energy

• Exothermic reaction happens when things go from high energy to lower energy

In contrast, endothermic reactions require an input of energy, leading to a decrease in entropy as the system absorbs energy and becomes more ordered.

An increase in no. of moles = a decrease in entropy.

• ΔG: The "final answer." If it's:

  • Negative (< 0), the reaction happens by itself (spontaneous).

  • Positive (> 0), the reaction doesn’t happen by itself (non-spontaneous).

• ΔH: The "heat energy" (enthalpy).

  • If negative (< 0), heat is released (like a fire—exothermic).

  • If positive (> 0), heat is absorbed (like boiling water—endothermic).

• ΔS: The "messiness factor" (entropy).

  • If positive (> 0), things get messier (more disorder, like ice melting into water).

  • If negative (< 0), things get more organised (less disorder, like water freezing into ice).

If the ΔS_system^ꝋ is positive:

• Both the first and second terms will be negative.

If the ΔS_system^ꝋ is negative:

• The first term is negative and the second term is positive