# How do I know if a double displacement reaction occurs?

Apr 7, 2017
1. Two compounds with positive and negative ions.
2. A difference in electro negativity or reactivity between the anions or cations.
3. One of the new compounds in the product must be somewhat insoluble so that it comes out of solution.

#### Explanation:

1. For a double replacement to take place there must be two positive and two negative ions.

$\left({A}^{+} {X}^{-}\right) + \left({B}^{+} {Y}^{-}\right) = = \left({A}^{+} {Y}^{-}\right) + \left({B}^{+} {X}^{-}\right)$

1. A must be able to replace B. This will only happen if A is more reactive that B.

2. $\left({A}^{+} {Y}^{-}\right)$must be insoluble so it forms a solid and comes out of solution.

May 12, 2017

You must make either (a) a precipitate or (b) a gas or (c) a nonelectrolyte.

#### Explanation:

A double displacement reaction is a chemical reaction in which two compounds react, and the positive ions (cations) switch partners with the negative ions (anions) to form two new products.

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(From Study.com)

(a) Formation of a precipitate

$\text{AgNO"_3"(aq)" + "NaCl(aq)" → underbrace("AgCl(s)")_color(red)("curdy white precipitate") + "NaNO"_3"(aq)}$

(b) Formation of a gas

"Na"_2"S(aq)" + "2HCl(aq)" → "2NaCl(aq)" + underbrace("H"_2"S(g)")_color(red)("gas with rotten egg smell")

(c) Formation of a nonelectrolyte

"NaOH(aq) + HCl(aq)" → "NaCl(aq)" + underbrace("H"_2"O(l)")_color(red)("a weak electrolyte")

"HCl(aq) + NaC"_2"H"_3"O"_2"(aq)" → "NaCl(aq)" + underbrace("HC"_2"H"_3"O"_2"(aq)")_color(red)("a weak electrolyte")