• The?entropy (S)?of a given system is the number of possible arrangements of the particles and their energy in a given system
  • In other words, it is a measure of how?disordered?or?chaotic?a system is
• When a system becomes?more disordered, its entropy will?increase
• An increase in entropy means that the system becomes?energetically more stable
• For example, during the thermal decomposition of calcium carbonate (CaCO₃) the entropy of the system increases:

CaCO₃(s) → CaO(s) + CO₂(g)

• • In this decomposition reaction, a gas molecule (CO₂) is formed
  • The CO₂?gas molecule is more disordered than the solid reactant (CaCO₃), as it is constantly moving around
  • As a result, the system has become more?disordered?and there is an?increase?in?entropy

• Another typical example of a system that becomes more disordered is when a solid melts
  • For example, melting ice to form liquid water:

H₂O(s) → H₂O(l)

• • The water molecules in ice are in fixed positions and can only vibrate about those positions
  • In the liquid state, the particles are still quite close together but are arranged more randomly, in that they can move around each other
  • Water molecules in the liquid state are therefore more?disordered
  • Thus, for a given substance, the?entropy?increases?when its solid form melts into a liquid
• In both examples, the system with the?higher?entropy?will be?energetically favourable?(as the energy of the system is more spread out when it is in a disordered state)

Melting a solid will cause the particles to become more disordered resulting in a higher entropy state