what are examples of chemical changes?

Answer 1

A chemical change is one that changes the molecular structure. Freezing water is not a chemical change because it is still water just in a different state. Burning a piece of wood is a chemical change because you have broken down the particles at a molecular state. A good way to determine if its chemical or physical change, is to figure out how hard it would be to change the substance back to its previous state. Ice let it melt. Ashes dont turn back into wood, even after the fire cools down. There are other ways to cause a chemical change, electricity, introduction of an acidic or basic agent and chemical reaction.

Answer 2

Chemical reactions, also called chemical changes, are not limited to happening in a chemistry lab. Here are some examples of chemical reactions with the corresponding chemical equations:

A silver spoon tarnishes. The silver reacts with sulfur in the air to make silver sulfide, the black material we call tarnish.
2 Ag + S Ag2S

An iron bar rusts. The iron reacts with oxygen in the air to make rust.
4 Fe + 3 O2 2 Fe2O3

Methane burns. Methane combines with oxygen in the air to make carbon dioxide and water vapor.
CH4 + 2 O2 CO2 + 2 H2O

An antacid (calcium hydroxide) neutralizes stomach acid (hydrochloric acid).
Ca(OH)2 + 2 HCl CaCl2 + 2 H2O

Glucose (simple sugar) ferments to ethyl alcohol and carbon dioxide. The sugar in grapes or from grain ferments with yeast to make the alcohol and carbon dioxide. The carbon dioxide is the gas that bubbles out of beer or champaign.
C6H12O6 (glucose) 2 C2H5OH (ethyl alcohol) + 2 CO2

Alcohol plus oxygen becomes vinegar and a molecule of water. As in the fermentation of glucose, this is a more complex reaction than it appears here because it is a biochemical reaction.
C2H5OH + O2 HC2H3O2 + H2O

As a general rule, biochemical happenings make poor examples of basic chemical reactions because the actual reaction is carried on within living things and under enzyme control.

Answer 3

Fermentation of sugars into alcohol

Burning of carbonaceous substances like charcoal, coal, oil etc. in air or oxygen to produce carbon dioxide.

Production of iron from iron ore (iron oxide) by reducing with coke.