Consider the entropy change in the following chemical or physical processes:
1.2 Na(s) + Cl₂(g) → 2 NaCl(s)
2. N₂(g) + 3 H₂(g) → 2 NH3(g)
3. H₂O(s)→ H₂O(l)
4. C10H22(1)→ C10H22(S)
5.2 Mg(s) + O₂(g) → 2 MgO(s)
In which of these processes is entropy increased?
Recall that entropy measures the number of microstates in a substance, which is highest in gases, followed by liquids and solids. Hence, entropy increases if the products have more gaseous molecules than the reactants.
In reaction one, chlorine gas is converted into solid NaCl, so entropy decreaes.
In reaction two, four moles of gas are converted into two moles of gas, so entropy decreases.
In reaction three, ice is melted to form water, which has higher entropy. Thus, entropy increases.
In reaction four, a liquid is freezed into its solid phase, leading to a decrease in entropy.
In reaction five, oxygen gas is converted into solid MgO, so entropy decreases.
