Question #b986f

1 Answer
Jan 20, 2014

Double replacements are not reversible because a pair of the ions is removed from the solution.

BY FORMING A PRECIPITATE

AgNO₃ + KCl → AgCl + KNO₃

The ionic equation is

Ag⁺(aq) + NO₃⁻(aq) + K⁺(aq) + Cl⁻(aq) → AgCl(s) + K⁺(aq) + NO₃⁻(aq)

Since silver chloride is insoluble in water, the Ag⁺ and Cl⁻ ions take each other out of the solution and become unavailable for the reverse reaction.

BY FORMING A GAS

Na₂S + 2HCl → H₂S + 2NaCl

The ionic equation is:

2Na⁺(aq) + S²⁻(aq) + 2H⁺(aq) + 2Cl⁻(aq) → H₂S(g) + 2Na⁺(aq) + 2Cl⁻(aq)

The H⁺ and S²⁻ ions form H₂S gas, which escapes into the atmosphere, so it cannot participate in the reverse reaction.

BY FORMING A NONELECTROLYTE

HCl(aq) + NaOH(aq) →HOH(l) + NaCl(aq) or

H⁺(aq) + Cl⁻(aq) + Na⁺(aq) + OH⁻(aq) → HOH(l) + Na⁺(aq) + Cl⁻(aq)

The H⁺ and the OH⁻ ions react to form water, which is a nonelectrolyte (does not form many ions). The H⁺ and the OH⁻ ions are removed from the solution.

Simple explanation, nice font are on this site: http://firstlightastro.com/DOWNLOADS/RXNS_Ch9_DD.pdf