Physics II / Phase Transitions and Critical Phenomena
Practice question · Multiple choice

Chemical potential equivalence determines phase coexistence, whereas free energy derivatives classify the transition order. Why does equal chemical potential not preclude a discontinuous jump in volume?

Hints
  1. Which thermodynamic derivative of the chemical potential yields the specific volume?
  2. Does the equality of two functions at a point guarantee that their gradients match?
Show the answer

B. Volume depends on the slope of chemical potential with pressure

Why

Chemical potential continuity means μ1=μ2\mu_1 = \mu_2, but its first derivative (μ/P)T=v(\partial \mu / \partial P)_T = v can differ across phases. Mistaking equal potentials for equal densities ignores derivative jumps. In second-order transitions, even higher derivatives remain coupled to distinct response functions.

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