For the freezing of water, represented by the equation H2O(l) → H2O(s), what are the signs of ΔH (enthalpy change) and ΔS (entropy change)?

• A. ΔH is positive, ΔS is negative
• B. ΔH is negative, ΔS is negative
• C. ΔH is negative, ΔS is positive
• D. ΔH is positive, ΔS is positive

Answer: (B)

Verified step by step guidance

1. Understand the physical process: freezing of water is the phase change from liquid (H2O(l)) to solid (H2O(s)).
2. Recall that freezing is an exothermic process because energy is released when water molecules form a solid lattice, so the enthalpy change (\$\Delta H\$) is negative.
3. Consider the entropy change (\$\Delta S\$): entropy measures disorder, and since a solid is more ordered than a liquid, the entropy decreases during freezing, so \$\Delta S\$ is negative.
4. Summarize the signs: for freezing, \$\Delta H < 0\$ (negative) and \$\Delta S < 0\$ (negative).
5. Use this understanding to select the correct answer choice that matches these signs.