Phase Changes

Learn the models, terms, and applications of phase changes.

Lesson 2 of 32 parts Practice Flashcards

1/2

Melting, Boiling, and Latent Energy

Objective: Connect constant-temperature transitions to changed particle arrangements.

During a phase transition at a particular pressure, energy transfer can change the arrangement and interactions of particles while temperature remains approximately constant for a pure substance undergoing an equilibrium transition. For melting or vaporization, Q = mL under stated conditions, where L is specific latent energy in J/kg; condensation or freezing releases energy to surroundings. For 0.5 kg with L = 200,000 J/kg, a complete transition requires 100,000 J. Boiling occurs throughout a liquid at its boiling temperature for the given pressure, whereas evaporation can occur at the surface below that temperature. Pressure and composition affect transition temperatures. A heating curve must identify both sloped warming regions and flat transition regions.

Worked examples

Try itFor m = 0.5 kg and L = 200,000 J/kg, how much energy is needed for a full transition?Show answer

1. Identify the relevant concept in this section. 2. Q = mL = 0.5 × 200,000. 3. Answer: 100,000 J

Swipe sideways to move between sections

Melting, Boiling, and Latent Energy

Objective: Connect constant-temperature transitions to changed particle arrangements.

Worked examples

Try itFor m = 0.5 kg and L = 200,000 J/kg, how much energy is needed for a full transition?Show answer

1. Identify the relevant concept in this section. 2. Q = mL = 0.5 × 200,000. 3. Answer: 100,000 J

Applications and Worked Problems

Objective: Apply phase changes to calculations, evidence, and specified situations.

A heating curve relates added energy to temperature. Within one phase, q=mcΔT approximates heating with constant specific heat. During an ideal phase transition at fixed pressure, temperature remains approximately constant while energy changes interactions and arrangement; use q=mL with the specified latent heat. A whole process may require adding separate heating and transition energies. Pure-substance plateaus and equilibrium assumptions are idealizations; mixtures and experimental losses complicate real curves.

Formulas

$q=mcΔT$
$q=mL$

Worked examples

Try itA 10 g sample has specific heat 4.18 J/(g·°C). What heat raises its temperature by 5 °C without a phase change?Show answer

1. Use q=mcΔT. 2. 10×4.18×5=209 J.

Try itA 10 g material has latent heat 334 J/g. How much energy is needed for the stated phase change at constant temperature?Show answer

1. Use q=mL during this phase change. 2. 10×334=3340 J.

You finished the reading!

Lock it in with a few practice questions, then move on to the next lesson.

Practice Next lesson

Previous lessonParticle Behavior Next lessonGas Relationships