Phase changes involve substances transforming between solid, liquid, and gas...
AP Chemistry15 views·Updated Jul 30, 2026·2 pagesUnderstanding Phase Changes in AP Chemistry 6.5
1
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Energy of Phase Changes and Phase Diagrams
When substances change phase, energy is either absorbed or released while the temperature remains constant. Endothermic phase changes (solid→liquid and liquid→gas) absorb energy, while exothermic phase changes (liquid→solid and gas→liquid) release energy. The energy absorbed in one direction equals the energy released in the reverse direction.
Phase diagrams show how substances exist at different temperatures and pressures. The triple point represents where a substance can exist simultaneously in all three phases. The critical point marks the highest combination of temperature and pressure at which a substance can exist between gas and liquid states.
Special phase transitions include sublimation (solid directly to gas) and deposition (gas directly to solid). These transitions bypass the liquid phase entirely and can be seen in everyday examples like dry ice.
Did you know? While most substances expand when melting, water is unique - it actually expands when freezing, which is why ice floats!
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of 2
Heating/Cooling Curves and State Changes
Heating curves show what happens as energy is added to a substance. During a phase change, the temperature stays flat while energy goes into breaking molecular bonds rather than increasing kinetic energy. This creates the characteristic "plateau" sections in heating curves.
When you add heat energy (endothermic process), substances move from solid→liquid→gas. The energy required for these transitions is called the heat of fusion (melting) and heat of vaporization. Removing heat energy (exothermic process) reverses the direction, moving from gas→liquid→solid.
A substance in the supercritical fluid region exists beyond the critical point where distinct liquid and gas phases no longer exist. This state has properties of both phases and is useful in industrial applications.
Remember this! During phase changes on a heating/cooling curve, temperature remains constant even though energy is being added or removed. All that energy goes into changing the arrangement of molecules, not increasing their speed.
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AP Chemistry15 views·Updated Jul 30, 2026·2 pagesUnderstanding Phase Changes in AP Chemistry 6.5
Phase changes involve substances transforming between solid, liquid, and gas states. These transformations follow predictable patterns that can be mapped on phase diagrams and visualized through heating and cooling curves.
1
of 2
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Energy of Phase Changes and Phase Diagrams
When substances change phase, energy is either absorbed or released while the temperature remains constant. Endothermic phase changes (solid→liquid and liquid→gas) absorb energy, while exothermic phase changes (liquid→solid and gas→liquid) release energy. The energy absorbed in one direction equals the energy released in the reverse direction.
Phase diagrams show how substances exist at different temperatures and pressures. The triple point represents where a substance can exist simultaneously in all three phases. The critical point marks the highest combination of temperature and pressure at which a substance can exist between gas and liquid states.
Special phase transitions include sublimation (solid directly to gas) and deposition (gas directly to solid). These transitions bypass the liquid phase entirely and can be seen in everyday examples like dry ice.
Did you know? While most substances expand when melting, water is unique - it actually expands when freezing, which is why ice floats!
2
of 2Sign up to see the content. It's free!
- Access to all documents
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Heating/Cooling Curves and State Changes
Heating curves show what happens as energy is added to a substance. During a phase change, the temperature stays flat while energy goes into breaking molecular bonds rather than increasing kinetic energy. This creates the characteristic "plateau" sections in heating curves.
When you add heat energy (endothermic process), substances move from solid→liquid→gas. The energy required for these transitions is called the heat of fusion (melting) and heat of vaporization. Removing heat energy (exothermic process) reverses the direction, moving from gas→liquid→solid.
A substance in the supercritical fluid region exists beyond the critical point where distinct liquid and gas phases no longer exist. This state has properties of both phases and is useful in industrial applications.
Remember this! During phase changes on a heating/cooling curve, temperature remains constant even though energy is being added or removed. All that energy goes into changing the arrangement of molecules, not increasing their speed.
We thought you’d never ask...
Our AI companion is specifically built for the needs of students. Based on the millions of content pieces we have on the platform we can provide truly meaningful and relevant answers to students. But its not only about answers, the companion is even more about guiding students through their daily learning challenges, with personalised study plans, quizzes or content pieces in the chat and 100% personalisation based on the students skills and developments.
You can download the app in the Google Play Store and in the Apple App Store.
That's right! Enjoy free access to study content, connect with fellow students, and get instant help – all at your fingertips.
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Practice converting between mass, moles, and number of particles using Avogadro's constant and the fundamental concept of the mole.
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Dipole dipole, hydrogen bonding, intermolecular forces versus Intramolecular bonds, dipole induced dipoles, London dispersion forces, ion dipole interactions, properties with intermolecular forces, comparing magnitude of IMFs
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Samantha KlichAndroid user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
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