Signs of a Chemical Change

A chemical change, also called a chemical reaction, involves combining two different substances together to form a new substance with different physical and chemical properties. In a chemical change the atoms of one substance are rearranged to form a new substance; matter, however, is never created or destroyed. There are five common signs to look for indicating that a chemical change is taking place.

Formation of a Precipitate

A precipitate is a solid formed during a chemical reaction between two liquids. The precipitate differs from both of the reactants and generally occurs when solutions containing ionic compounds are mixed. According to Harper College, a precipitate can be identified by examining solubility rules.

Color Change

A color change generally signals that a chemical change has taken place. An exception would be two substances combined together that do not react yet change color because of dilution. Rhode Island College cites the changing color of leaves and food that has spoiled as two examples of color changes in a chemical reaction.

Production of Gases

If the reaction between two liquids or a solid and a liquid gives off gases, it is likely that a chemical change has occurred. Small bubbles that form inside the liquid underneath the surface are enough to indicate a chemical reaction is taking place.

Temperature Change

When two substances are combined, any increase or decrease in temperature is a sign of a chemical change. If the temperature rises and gives off heat, the reaction is said to be exothermic. A drop in temperature indicates that the reaction is endothermic--or absorbing heat. The temperature may change very suddenly or occur over a long period of time.

Light or Sound

The presence of light or audible sound emitted during a reaction would imply that it is a chemical reaction. When a substance is altered, light and sound indicate quick changes in temperature. A fireworks display is a good example of the presence of light and sound during a chemical reaction.

References

• Chemical Changes
• Signs of a Reaction
• Physical and Chemical Changes