Chemical+Reactions

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EXAMPLES OF CHEMICAL CHANGES

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 Ag 2 S

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

[|Methane] burns. Methane combines with oxygen in the air to make carbon dioxide and water vapor. CH 4 + 2 O 2 -> CO 2 + 2 H 2 O

An antacid (calcium hydroxide) neutralizes stomach acid (hydrochloric acid). Ca(OH) 2 + 2 HCl -> CaCl 2 + 2 H 2 O

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. C 6 H 12 O 6 ( glucose ) -> 2 C 2 H 5 OH ( ethyl alcohol ) + 2 CO 2

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. C 2 H 5 OH + O -> HC 2 H 3 O 2 + H 2 O

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.

EXAMPLES OF PHYSICAL CHANGES

Here are some examples of changes that are NOT chemical reactions. In each case, the original material or materials may be reclaimed by physical processes.

Water boils out of a kettle or condenses on a cold glass. An aluminum pot is put on a burner and gets hot. Dry ice goes from a solid to a gaseous form of carbon dioxide (// sublimation //). Gold melts or solidifies. Sand is mixed in with salt. A piece of chalk is ground to dust. Glass breaks. An iron rod gets magnetized. A lump of sugar dissolves in water.