Heat

Thermochemistry

Learning Objectives

  • Define heat.
  • Define thermochemistry.

 

Examples

Heat is needed to make an iron bar malleable

“Under the spreading chestnut tree …”

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

Figure 17.3

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.

Key Takeaways

Summary

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

 

Exercises

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?

Glossary

  • heat: Energy that is transferred from one object or substance to another because of a difference in temperature between them.
  • thermochemistry: The study of energy changes that occur during chemical reactions and during changes of state.