ENTROPY
1.1 Defining entropy
The entropy (S) of a given system is the number of possible arrangements of the particles and their
energy in a given system (how disordered a system is)
All elements have positive standard molar entropy values
When a system becomes more disordered, its entropy will increase more stable
Factors affecting entropy values
The order of entropy for the different states of matter: gas > liquid > solid.
Simpler substances with fewer atoms have lower entropy values than complex substances with
more atoms
Harder substances have lower entropy than softer substances of the same type
Thermal decomposition of calcium carbonate (CaCO3)
o The CO2 gas molecule is more disordered than the solid reactant (CaCO3), as it is constantly
moving around increase in entropy of the system
o CaCO3(s) → CaO(s) + CO2(g)
The formation of ammonia in the Haber process
o There are four gas molecules (1 nitrogen and 3 hydrogen molecules) in the reactants
o There are two gas molecules (2 ammonia molecules) in the products
o A decrease in entropy – the products are less stable than the reactants
o N2(g) + 3H2(g) ⇋ 2NH3(g)
1.2 Calculating entropy
The equation of standard entropy change of a system is: ΔSsystemꝋ = ΣSproductsꝋ - ΣSreactantsꝋ
1.1 Defining entropy
The entropy (S) of a given system is the number of possible arrangements of the particles and their
energy in a given system (how disordered a system is)
All elements have positive standard molar entropy values
When a system becomes more disordered, its entropy will increase more stable
Factors affecting entropy values
The order of entropy for the different states of matter: gas > liquid > solid.
Simpler substances with fewer atoms have lower entropy values than complex substances with
more atoms
Harder substances have lower entropy than softer substances of the same type
Thermal decomposition of calcium carbonate (CaCO3)
o The CO2 gas molecule is more disordered than the solid reactant (CaCO3), as it is constantly
moving around increase in entropy of the system
o CaCO3(s) → CaO(s) + CO2(g)
The formation of ammonia in the Haber process
o There are four gas molecules (1 nitrogen and 3 hydrogen molecules) in the reactants
o There are two gas molecules (2 ammonia molecules) in the products
o A decrease in entropy – the products are less stable than the reactants
o N2(g) + 3H2(g) ⇋ 2NH3(g)
1.2 Calculating entropy
The equation of standard entropy change of a system is: ΔSsystemꝋ = ΣSproductsꝋ - ΣSreactantsꝋ
