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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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Heat is needed to make an iron bar malleable

Credit: Gemma Stiles
Source: http://www.flickr.com/photos/gemmastiles/6927436488/
License: CC BY-NC 3.0

“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.

Heat flows from a warm object to a cold object

Credit: CK-12 Foundation - Christopher Auyeung
License: CC BY-NC 3.0

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. [Figure2]

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.

Practice

Questions

Use the link below to answer the following questions:

http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/heat.html

  1. What is the correct term for the “heat” an object possesses?
  2. How do we increase the internal energy of an object?
  3. What is the internal energy a result of?

Review

Questions

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

Image Attributions

  1. [1]^ Credit: Gemma Stiles; Source: http://www.flickr.com/photos/gemmastiles/6927436488/; License: CC BY-NC 3.0
  2. [2]^ Credit: CK-12 Foundation - Christopher Auyeung; License: CC BY-NC 3.0

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Difficulty Level:

At Grade

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Date Created:

May 01, 2013

Last Modified:

Feb 27, 2015
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