Descriptions of Chemical Changes (Reactions)
1. Colorless hydrogen gas was mixed with colorless oxygen gas. Spark was introduced into the
system. Rapid exothermic reaction occurred. Water vapor was produced.
2. Elemental sulfur (S8) with yellow color was burned in the air. The oxygen in the air reacted with
sulfur element to form sulfur trioxide.
3. Upon heating, solid mercury(II) oxide decomposes into liquid mercury metal and releases
oxygen gas in the process.
4. Hydrochloric acid (HCl) aqueous solution was added to zinc metal. Gas bubbles formed.
Subsequent analysis on the gas produced indicated that it was hydrogen gas. In addition,
aqueous solution containing zinc chloride was also produced.
5. When a small piece of shining sodium metal was added to water containing phenolphthalein pH
indicator, gas bubbles formed and the sodium metal piece quickly became smaller and
disappeared. Solution quickly turned pink in color. The gas released was subsequently analyzed
to be hydrogen gas. And the other product was sodium hydroxide which turned the
phenolphthalein indicator pink.
6. Photosynthesis process is used by all the plant species to produce sugar (C6H12O6). Plants use
carbon dioxide and water to produce sugar (C6H12O6) and oxygen gas simultaneously.
7. Aqueous solution of iron(III) sulfate was mixed with potassium hydroxide solution. White
precipitate was observed to form immediately upon mixing. The white precipitate was
subsequently analyzed to be iron(III) hydroxide, and aqueous solution of potassium sulfate was
produced simultaneously.
8. Solid aluminum reacts violently with solid iron(II) oxide to form aluminum oxide and elemental
iron.
9. Phosphorus element (P4) reacts with oxygen gas in air to form diphosphorus pentaoxide
compound.
10. When dilute hydrochloric acid was added to solid sodium carbonate powder, gas bubble
formed. The gas produced was later analyzed to be carbon dioxide. Meanwhile, aqueous
sodium chloride solution and pure water were produced.
11. When concentrated sulfuric acid (H2SO4) was slowly added to hydrogen iodide, dihydrogen
sulfide gas, purple iodine solid and water were produced.
12. Iron rusts when exposed to the outside elements. Chemical change associated with the rusting
is that elemental iron reacts with oxygen gas to form reddish iron(III) oxide.
13. Very few chemical reactions involve noble gases. Here’s one: xeon gas is mixed with fluorine
gas, the reaction is initiated by an electrical spark. Xeon hexafluoride is the sole product.
14. Propane (C3H8) is the common fuel used in outdoor barbeque. Combustion is the chemical
change propane undergoes to release large amount of heat. The other reactant is oxygen gas,
and products are carbon dioxide gas and water vapor.
15. Solid potassium chlorate is thermally unstable. Under heating, it decomposes into potassium
powder and releases oxygen gas.
16. Hydrogen peroxide solution decomposes spontaneously into liquid water and oxygen gas upon
addition of trace amount of iron catalyst.
17. Hydrofluoric acid (HF) dissolves solid silicon dioxide to form silicon tetrafluoride gas and pure
water.