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# 17.2: Heat

Difficulty Level: At Grade Created by: CK-12
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Practice Chemical Heat

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#### “Under the spreading chestnut tree ...” - The Village Blacksmith by Henry Wadsworth Longfellow. 1807-1882

Blacksmiths, like the one mentioned in Longfellow's poem, heat solid iron in order to shape it into a variety of different objects. Iron is a rigid, solid metal. At room temperature, it is extremely difficult to bend iron. However, when heated to a high enough temperature, iron can be easily worked. The heat energy in the forge is transferred to the metal, making the iron atoms vibrate more and move around more readily.

### Heat

Heat is energy that is transferred from one object or substance to another because of a difference in temperature between them. Heat always flows from an object at a higher temperature to an object a lower temperature (see Figure below). The flow of heat will continue until the two objects are at the same temperature.

Object A starts with a higher temperature than object B. No heat flows when the objects are isolated from each other. When brought into contact, heat flows from A to B until the temperatures of the two objects are the same.

Thermochemistry is the study of energy changes that occur during chemical reactions and during changes of state.  When chemical reactions occur, some chemical bonds are broken, while new chemical bonds form. As a result of the rearrangement of atoms, the total chemical potential energy of the system either increases or decreases.

### Summary

• Heat is transferred energy from a site of higher energy to a site of lower energy.

### Review

1. What is heat?
2. In which direction does heat flow?
3. What does thermochemistry involve?

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Date Created:
May 01, 2013