Materials scienceLesson 2 of 3 in the course Metals and alloys

Reading Pure-Substance, Alloy, and Mixture Phase Diagrams

5 flashcards · 5 quiz questions · 5 match pairs · 5 fill-in sentences · English

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Summary

A pressure–temperature phase diagram shows which phase of a substance is stable under different conditions. It helps explain when a material melts, boils, freezes, or changes directly between solid and gas.

A phase diagram is a map of conditions, commonly temperature and pressure, at which phases are stable. For a simple substance, the main phases shown are solid, liquid, and gas. Each open region usually represents a single phase.

All flashcards

What is a phase diagram?
A map showing the conditions under which phases are stable and how they change with variables such as temperature, pressure, or composition.
What is a phase boundary?
A line separating phase regions; the neighboring phases can coexist in equilibrium along it.
What is the triple point?
The unique temperature and pressure at which three phases coexist in stable equilibrium.
What is the critical point?
The endpoint of the liquid–gas boundary, beyond which liquid and gas are indistinguishable.
Why does pressure lower the melting temperature of ice?
Ice is less dense than liquid water, so melting decreases volume; higher pressure therefore favors the liquid.

Quiz questions

  1. In a single-component pressure–specific-volume–temperature diagram, how are equilibrium states represented?Answer: As surfaces in three-dimensional state space.
  2. At fixed pressure, what does a horizontal tie line on a binary boiling-point diagram connect?Answer: The equilibrium liquid and vapor compositions.
  3. How is composition represented in a ternary phase diagram at fixed pressure?Answer: By points within an equilateral composition triangle.
  4. Why is mole fraction often preferred to molarity for describing binary-mixture composition?Answer: Mixture volume and density can vary with temperature and composition.
  5. What do iso-lines on a phase diagram represent?Answer: States that share the same value of an additional property.

Based on the Wikipedia article Phase diagram, licensed CC BY-SA 4.0. Adapted into a summary, flashcards and quizzes.

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