📚 Learning Guide
States of Matter
hard

When considering the transition of a substance from a liquid to a gas at its boiling point, which factors most significantly influence the molecular motion and energy of the substance as it approaches its critical point?

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Choose the Best Answer

A

Increased temperature and decreased pressure lead to enhanced molecular translation and reduced intermolecular forces.

B

Decreased temperature and increased pressure result in strong molecular vibrations but limit translational motion.

C

Constant temperature and pressure maintain the same level of molecular rotation without affecting the state.

D

Increased molecular mass and potential energy contribute to a slower transition between states.

Understanding the Answer

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Answer

At the boiling point, the temperature is high enough that the kinetic energy of molecules equals the energy needed to overcome intermolecular forces, so the liquid begins to vaporize. As the substance approaches its critical point, the pressure needed to keep it liquid rises while the temperature stays nearly constant, so molecules move more rapidly and the distinction between liquid and gas blurs. The main factors that drive this change are the increasing temperature, the decreasing strength of intermolecular attractions, and the rise in pressure that squeezes molecules closer together. Because the kinetic energy grows, molecules escape more easily, and the latent heat of vaporization diminishes until the two phases merge. For example, when water is heated near 374 °C and 22.

Detailed Explanation

When the temperature rises, each molecule gets more kinetic energy, so it moves faster and more often. Other options are incorrect because Cooling the liquid actually reduces energy, so molecules vibrate less, not more; Keeping temperature and pressure fixed does not stop a liquid from turning into gas.

Key Concepts

Molecular Motion
Critical Point
Changes of State
Topic

States of Matter

Difficulty

hard level question

Cognitive Level

understand

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