Final answer:
A double displacement reaction occurs when the cations and anions from two compounds switch places to form new compounds. The reaction is balanced by ensuring that the number of atoms on both sides of the equation is the same.
Step-by-step explanation:
A double displacement reaction, also known as a double replacement reaction, occurs when the cations and anions from two compounds switch places to form new compounds. The reaction is balanced by ensuring that the number of atoms on both sides of the equation is the same.
For example, the balanced equation for the double displacement reaction between sodium cyanide (NaCN) and hydrobromic acid (HBr) is:
NaCN(aq) + HBr(aq) → HCN(g) + NaBr(aq)
In this reaction, the cations Na+ and H+ switch places to form the new compounds HCN and NaBr.