Heat Changes Associated with Physical Changes; Heating Curves

Substances change state through six different processes. Each of these processes occurs at different temperatures. Some of the phase changes occur during the heating of the substance. Other processes occur during the cooling of the substance. The six processes are melting, freezing, vaporization, condensation, sublimation, and deposition.

Heating Curves

The heating process can begin with a solid and lead to a gas. As more heat is added to the substance, the substance will change phases. In this interactivity, click NEXT to learn about the different phase changes that exist as solid water turns into a gas, and how these changes can be viewed on a heating curve.

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Cooling Curves

The cooling process is the exact opposite on the heating process. With this example of water, the cooling process begins with steam. The steam will cool and become a liquid, and then a solid. Just like the heating curve, the cooling curve has phase changes at 100°C and O°C. In this activity, click NEXT to learn about the different phase changes that exist as water vapor turns into a solid, and how these changes can be viewed on a cooling curve.

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Sublimation and Deposition

Sublimation occurs when particles change directly from solid phase into a gas without first changing into a liquid. Carbon dioxide is a common example of a compound that sublimates at atmospheric pressure. You may have even seen this process take place. Frozen carbon dioxide is better known as dry ice. Dry ice, which sublimes at -78 °C, is used to prepare freeze-dried foods for long-term storage.

Deposition is the process that is exactly opposite of sublimation. Deposition occurs when a gas changes phases directly into a solid without first changing into a liquid. One common example of deposition is snow. Snow forms in clouds when gaseous water vapor turns into a snow flake without becoming a liquid first.

 

Phase Changes and Heating Curves Review

Review your knowledge of phase changes and heating curves in this non-graded activity. Answer each of the questions by following the instructions on each provided. Then, click SUBMIT to check your response. Click on the activity thumbnail, and then click NEXT to get started.