Entropy Change Calculator

Entropy is a thermodynamic quantity that measures the degree of disorder or the dispersal of energy within a system. The second law of thermodynamics states that the total entropy of an isolated system never decreases over time: natural processes tend toward greater disorder. This calculator covers two common ways to quantify entropy change. The first is the classical heat-transfer formula: deltaS equals Q divided by T, where Q is the heat added to the system in joules and T is the absolute temperature in kelvin at which the transfer occurs. This formula applies to reversible processes at constant temperature, such as melting or boiling at the equilibrium point. A positive deltaS means heat entered the system and disorder increased; a negative deltaS means heat left. The second mode applies to the isothermal expansion of an ideal gas, where the volume changes from V1 to V2 at constant temperature. The formula is deltaS equals n times R times the natural logarithm of V2 divided by V1, where n is the number of moles and R is the universal gas constant 8.314 J per mol per K. Expanding the gas (V2 greater than V1) increases entropy because the molecules have more space to occupy. Enter your values and choose the mode that fits your problem. Temperature must be in kelvin. This calculator is suited to students studying thermodynamics, chemistry and engineering, and is for educational use.

Temperature must be in kelvin (K). For Celsius, add 273.15. Results apply to reversible processes at constant temperature only.