What is a double-replacement reaction in chemistry?

1 Answer
Apr 25, 2017

Answer:

See explanation

Explanation:

Double replacement (sometimes referred to as double displacement) reactions are when parts of ionic compounds are switched to form two new ionic compounds.

Heres an image:
enter image source here

The way I think of it, since we're dealing with ionic compounds, is that when I write out a reaction I begin like this.

#color(green) (A^+)color(red)(B^-) + color(purple)(C^+)color(red)(D^-)->?+?#

We swap the anions so that #A# is now with #D# and #C# is now with #B# Visually,

#color(green) (A^+)color(red)(B^-) + color(purple)(C^+)color(red)(D^-)->color(green) (A^+)color(red)(D^-)+ color(purple)(C^+)color(red)(B^-)#

Heres an real example:

Say you have Sodium Cyanide and you react it with Hydrogen Bromide:

#color(green)(Na)color(red)(CN)_(aq) + color(purple)(H)color(red)(Br)_(aq)->?+?#

Well we have to remember what are the charges of cation and anion. Since this is an easy example, they all have a charge of +1 for the cations and -1 for the anions but we can just write #+ or -#

#color(green)(Na^+)color(red)(CN^-)_(aq) + color(purple)(H^+)color(red)(Br^-)_(aq)->?+?#

Next we can just switch the anions to get

#color(green)(Na^+)color(red)(CN^-)_(aq) + color(purple)(H^+)color(red)(Br^-)_(aq)->color(green)(Na^+)color(red)(Br^-)_(aq)+color(purple)(H^+)color(red)(CN^-)_(g)#

(This forms Hydrogen cyanide gas by the way)

I'm not the best at explaining chemistry so if this was confusing I apologize and recommend checking out Tyler DeWitt's video on "Types of Chemical Reactions" as well as the his videos.