What is a chemical change?

Question

Caleb Adams · Accepted Answer

A chemical change is any change that results in the formation of new chemical substances with new properties.

For example, hydrogen reacts with oxygen to form water. This is a chemical change.

2H₂ + O₂ → H₂O

Hydrogen and oxygen are both colourless gases, but water is a liquid at ordinary temperatures.

EXAMPLES

Which of the following are chemical changes? (a) Sugar dissolves in warm water. (b) A nail rusts. (c) A glass breaks. (d) A piece of paper burns. (e) Iron and sulfur form a shiny nonmagnetic grey substance on heating.

Solutions:

(a) Not a chemical change. The sugar and water are still present.
(b) A chemical change. The reddish-brown rust is different from the iron.
(c) Not a chemical change. The glass is just in smaller pieces.
(d) A chemical change. The paper disappears. All that remains is a small amount of ash.
(e) A chemical change. Sulfur is yellow, and iron is magnetic. The product is neither yellow nor magnetic.

Here is video of a lab with a number of examples of both chemical and physical changes.

video from: Noel Pauller

Cooper Adams · Answer

undefined Chemical changes, such as combustion, rusting, fermentation, and digestion, are processes in which one or more substances go through a chemical reaction that produces new substances with different chemical compositions and properties compared to the original substances. Typically, this type of change involves the breaking and forming of chemical bonds between atoms.

Axel Alvarado · Answer

undefined A chemical change, also known as a chemical reaction, refers to the process in which one or more substances (reactants) are transformed into one or more different substances (products). During a chemical change, chemical bonds are broken and new bonds are formed, resulting in the creation of entirely new substances with different chemical properties than the original reactants. This transformation involves the rearrangement of atoms and molecules at the molecular level. Unlike physical changes, which only alter the physical state or appearance of a substance without changing its chemical composition, chemical changes involve the alteration of chemical composition and the formation of new substances with distinct chemical properties. Examples of chemical changes include combustion, oxidation, decomposition, and synthesis reactions.