Modification of Richard's rule and correlation between entropy of fusion and allotropic behaviour

Abstract

Richard's rule states that the entropy of fusion is a constant for metals and nearly equal to 2.2 cal K^—1 mol^—1. However, this rule is not found to be universally applicable. It is shown here that if the changes in entropy at all the transformation temperatures are added, the result is approximately a constant with a value of ∼ 2.2 cal K⁻¹ mol⁻¹. This parameter has been termed the cumulative entropy of fusion. Its approximately constant value suggests that there is a simple relationship between the entropy of fusion and the phase transition, which is very widely. followed among metallic elements.