Scope, Sequence, and Coordination

A Framework for High School Science Education

Based on the National Science Education Standards


Heat Energy Released or Absorbed in Chemical Reactions

Energy Transformations in Chemical Reactions
Chemical reactions may release or consume energy. Some reactions such as the burning of fossil fuels release large amounts of energy by losing heat and by emitting light. Light can initiate many chemical reactions such as photosynthesis and the evolution of urban smog.


Further Description:

Chemical reactions either release or absorb energy. This is frequently evident by a change of temperature or the evolution of light. Temperature changes can be measured in the laboratory and also predicted by calculation using knowledge of specific heats and heats of reaction.

Characteristic energy changes result from reorganization of atoms in chemical reactions. Different structural arrangements of the same atoms vary in energy content. Such energy changes can be computed using thermodynamic tables.


Concepts Needed:

Grade 9

Temperature, specific heat

Grade 10

Endothermic, exothermic

Grade 11

Molecular structure, standard state, heat of reaction, entropy, enthalpy

Grade 12

Heat of formation, free energy


Empirical Laws or Observed Relationships:

Endothermic and exothermic reactions


Theories or Models:

Gibbs free energy, first and second laws of thermodynamics


Page 66 in

Micro-Unit Description:

Heat Energy Released or Absorbed in Chemical Reactions
Students should measure the heat released or absorbed during chemical reactions in relation to the masses of the substances involved.


National Science Teachers Association
1840 Wilson Boulevard
Arlington VA 22201-3000
703.243.7100
www.nsta.org