Scope, Sequence, and Coordination

A Framework for High School Science Education

Based on the National Science Education Standards


Physical vs. Chemical Change

Mass and Number Conservation in Chemical Reactions
Chemical reactions occur all around us, for example in health care, cooking, cosmetics, and automobiles. Complex chemical reactions involving carbon-based molecules take place constantly in every cell in our bodies.


Further Description:

Chemical changes can be distinguished from physical changes on the macroscopic and microscopic levels. In a chemical change one or more substances with different characteristic properties are produced. At the macroscopic level a chemical change can often be recognized by transfer of energy, changes of state (such as formation of a solid or gas), and color changes. In both chemical and physical changes, conservation of mass and energy are observed.

Chemical reactions can be represented using word equations and symbols. The coefficients of balanced formula equations represent both molecules and collections of molecules (moles). Quantitative predictions about the amounts of reactants and products can be made from information about the balanced equation when additional information such as atomic mass is available. Qualitative predictions about chemical reactivity and representation of the reactions using equations for elements in Groups IA, IIA, and VIIA can be made based on the position of these elements in the periodic table.


Concepts Needed:

Grade 9

Physical change, chemical change/reaction, word equation, chemical symbol, changes of state, states of matter, solid, liquid, gas, color, chemical formula, element, compound, atom, molecule, reactants, products, solution

Grade 10

Balanced equation

Grade 11

Mole, molar mass

Grade 12

None suggested


Empirical Laws or Observed Relationships:

Periodic law


Theories or Models:

Conservation of mass and energy, conservation of atoms in chemical reactions


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Micro-Unit Description:

Physical vs. Chemical Change
Students should observe matter undergoing change and classify the change as chemical or physical from observation of the products and the energy absorbed or released. They should infer that mass is conserved when reactions producing a gas or a precipitate are observed.


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