# How does a double displacement reaction work? [closed]

When a double displacement reaction occurs with compound AB and CD, what determines that B and C are going to bond instead of A and C?

Double displacement reactions involve ionic compounds, i.e. salts formed from positive cations and negative anions. Consider the following setup, $$\ce{\color{blue}{A^{+}}\color{red}{B^{-}} + \color{blue}{C^{+}}\color{red}{D^{-}} -> \color{blue}{A^{+}}\color{red}{D^{-}} + \color{blue}{C^{+}}\color{red}{B^{-}}}$$ where the cations are indicated in blue and anions in red (and all charges are $$\pm 1$$ to reflect your question). All salts are comprised of cations and anions, hence $$\ce{\color{blue}{AC}}$$ wouldn't form since both are cations. $$\ce{\color{blue}{C}\color{red}{B}}$$ would form instead.