Measure of disorder in a system is called

• A. Enthalpy
• B. Internal energy
• C. Temperature
• D. Entropy

Answer: (D)

Disorder or randomness of the molecular arrangement is quantified by entropy. Entropy counts the number of ways a system’s molecules can be arranged (microstates) without changing its overall state; more possible arrangements mean higher entropy. In statistical terms, S is proportional to the logarithm of the number of microstates, S = k ln W. Enthalpy and internal energy describe energy content, while temperature describes average kinetic energy; neither is a direct measure of how mixed or disordered the system is. For instance, melting a crystalline solid into a liquid increases disorder and, thus, entropy, and mixing gases also raises entropy. Hence the measure of disorder is entropy.