Writing Balanced Chemical Equations (2):
13. Zinc metal reacts with hydrochloric acid to produce dissolved zinc chloride
and gaseous hydrogen.
Zn(s) + 2 HCl(aq)  ZnCl2(aq) + H2(g)
15. Pure hydrogen gas burns in atmospheric oxygen to produce water vapor.
2 H2(g) + O2(g)  2 H2O(g)
17. Silver metal dissolves in concentrated nitric acid, producing brown NO2
gas, water, and dissolved silver nitrate.
Ag(s) + 2 HNO3(aq)  NO2(g) + H2O(g) + AgNO3(aq)
19. Elemental boron is produced by heating solid diboron trioxide with
magnesium metal. Also produced in the reaction is solid magnesium oxide.
B2O3(s) + 3 Mg(s)  2 B(s) + 3 MgO(s)
21. Phosphorus trichloride, a highly toxic fuming liquid, is used in the
manufacture of certain pesticides. It is synthesized by direct combination of
white phosphorus gas (P4) and chlorine gas.
P4(g) + 6 Cl2(g)  4 PCl3(l)
23. Nitrous oxide gas (systematic name: dinitrogen monoxide) is used in
dentistry as an anesthetic. Nitrous oxide (and water vapor as a by-product) can be
produced in small quantities in the laboratory by careful heating of ammonium
nitrate.
2 NH4NO3(s)  N2O(g) + 2 H2O(g)
25. Acetylene gas (C2H2) is often used is used for welding because it burns in
oxygen with an intensely hot flame. The products of the combustion are carbon
dioxide gas and water vapor.
2 C2H2(g) + 5 O2(g)  4 CO2(g) + 2 H2O(g)
27. Barium can be produced in the solid elemental state by the reaction of solid
barium oxide with aluminum metal at high temperatures. Solid aluminum oxide
is a by-product.
3 BaO(s) + 2 Al(s)  3 Ba(s) + Al2O3(s)
29. Carbon tetrachloride is a liquid solvent widely used for many years in the
dry cleaning industry until its harmful properties became well known. It is
prepared by reacting natural gas (methane, CH4) and chlorine gas in the presence
of ultraviolet light. Hydrogen chloride gas is a by-product.
CH4(g) + 2 Cl2(g)  CCl4(l) + 2 H2(g)