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Heating Curves

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Heating Curves

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Lesson Focus

Heating Curves


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You will investigate the relationship between the phases of matter and temperature.

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Now You Know

After completing this tutorial, you will be able to complete the following:

  • Explain that the amount of a substance does not affect its boiling point.
  • Explain that at a constant heating rate, the greater the quantity of one substance, the longer it takes to reach its boiling point.
  • Describe salt water as having a higher boiling point than pure water.
  • Explain that the greater the heating rate the faster a substance will reach its boiling point.
  • Interpret a graph of a heating curve for a substance and identify the boiling point of the substance.

Everything You'll Have Covered

Heating curves show the process of phase change. Heating curves represent the relationship between heating rate and temperature. The heat that flows into the material is a combination of an increase of internal energy and work.

Heat added to a system can have one of two effects on a substance: (1) it can increase the temperature of the substance, or (2) it can cause a phase change. It cannot have both effects at the same time. Temperature does not change during a phase transition.

The heating curve consists of a series of diagonal lines and plateaus. The diagonal lines represent changes in temperature, and the plateaus represent phase changes. When heat is added to a solid below its melting point, the temperature begins to rise. Rising temperature means that the average kinetic energy of the particles is increasing. If the solid is heated at its melting point, the heating curve shows that the temperature remains a constant flat, horizontal line until the solid has completely melted. This is because the melting process requires energy. After the entire solid has melted, heating the liquid raises its temperature until the boiling point is reached. As the temperature increases, a linear, sloped line will correspond to the heating curve. Heat added to the liquid at its boiling point is absorbed as the liquid boils at a constant temperature. After all the liquid has been vaporized, and the system is entirely gaseous, the addition of more heat raises the temperature of the gas in the enclosed system.

Tutorial Details

Approximate Time 20 Minutes
Pre-requisite Concepts Learners should be familiar with phases of matter.
Course Chemistry
Type of Tutorial Experiment
Key Vocabulary 3D, boiling, concentration