For example, look at the first process you've listed. Is the salt used up? If you want to say "yes", take a look at the road or sidewalk after the water dries up. Is the snow used up? Is water a new chemical substance? If you want to say "yes", ask yourself if water and snow have different chemical formulas.
For example, 2 Na + Cl2 = 2 NaCl is a redox reaction, because the sodium's oxidation number changes from 0 to +1, and the chlorine's oxidation number changes from 0 to -1. All combustion reactions and all formation reactions (in which compounds form from elements) are redox reactions. But there are other possibilities, too.
Hint: Alka Seltzer tablets contain sodium bicarbonate and citric acid. When dropped into water, sodium citrate, carbon dioxide, and water are formed. Look up the chemical formulas for each of these substances, assign oxidation numbers, and decide whether this is a redox reaction or not.
Author: Fred Senese firstname.lastname@example.org
Copyright © 1997-2010 by Fred Senese
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Last Revised 08/17/15.URL: http://antoine.frostburg.edu/chem/senese/101/reactions/faq/print-recognizing-redox-reactions.shtml