State of Matter | Grade 6 | Unit 2 - Concept 1 - Lesson 2 | Science

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In This Lesson:
Thermal energy:
Kinetic energy is the energy that molecules and atoms of a substance has due to their motion.
Thermal energy of a substance relates to kinetic energy of its molecules and atoms, where:
Thermal energy of a substance is the total sum of kinetic energy of its molecules and atoms.
Example:
The molecules of solids are not moving as fast as molecules of liquids, so solids have less thermal energy than liquids.
Thermal energy (heat) transfers from one substance to another if they have different temperatures, where:
Heat flows from a hotter substance to a colder substance.
Example:
If you hold ice cubes in your hand that has more thermal energy than the ice cubes, so the ice cubes will melt because heat flows from your hand (hotter substance) to the ice cubes (colder substance).
When a substance is heated:
Thermal energy is transferred to the molecules of the substance.
Then, the molecules gain thermal energy and move faster, and this causes
• The total kinetic energy of the molecules increases.
• The temperature of substance increases.
The following table shows the changes from solid state to liquid state and the opposite change from liquid state to solid state at certain temperatures.
 
The following table shows the change from liquid state into gas state and the
opposite change from gas state to liquid state at certain temperatures.
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