Signs of Chemical Reactions From Lab Experiments

Chemical reactions involve the rearrangement of atoms within molecules to produce new compounds. As the atoms of a compound are rearranged in a chemical reaction, energy is released and absorbed as bonds are created and broken, resulting in a net change of energy.

Temperature Change

One form of the energy released or absorbed in a chemical reaction is heat. Exothermic reactions release heat energy (raise temperature) whereas endothermic reactions absorb heat (lower temperature).

Light

Light is another form of energy. Some energy released in a chemical reaction may take the form of light.

Gas Bubbles

The appearance of gas bubbles may indicate a chemical change when a product of the reaction is released as a gas. Note, though, that gas bubbles also form at the boiling point of a substance, which is not a chemical change.

Precipitate

In solutions, a reaction may result in the appearance of a precipitate, an insoluble material that appears in a liquid. Freezing a liquid into a solid, though, is not a chemical reaction.

Color Change

Many reactions will produce a color change in the reactants. This color change indicates the occurrence of a chemical reaction.

Other Changes in Physical and Chemical Properties

A change in any property that characterizes a substance may indicate a chemical reaction. These properties include density, reactivity, melting point, boiling point, smell, and taste.

References

• Balancing Chemical Chemistry
• Signs of a Reaction
• Chemical Changes