Question

which chemical equation represents a double replacement reaction?
2na + cl₂ → 2nacl
zn + 2hcl → zncl₂ + h₂
2kclo₃ → 2kcl + 3o₂
naoh + hcl → nacl + h₂o

Explanation:

Step1: Recall double replacement reaction

A double replacement reaction is a type of chemical reaction where two compounds exchange ions to form two new compounds. The general form is \(AB + CD
ightarrow AD + CB\).

Step2: Analyze each option

• Option 1: \(2\text{Na} + \text{Cl}_2

ightarrow 2\text{NaCl}\)
This is a combination (synthesis) reaction, where two substances combine to form one. So not double replacement.

• Option 2: \(\text{Zn} + 2\text{HCl}

ightarrow \text{ZnCl}_2 + \text{H}_2\)
This is a single replacement reaction, where one element replaces another in a compound. So not double replacement.

• Option 3: \(2\text{KClO}_3

ightarrow 2\text{KCl} + 3\text{O}_2\)
This is a decomposition reaction, where one compound breaks down into two or more substances. So not double replacement.

• Option 4: \(\text{NaOH} + \text{HCl}

ightarrow \text{NaCl} + \text{H}_2\text{O}\)
Here, \(\text{NaOH}\) (where \(A=\text{Na}^+\), \(B=\text{OH}^-\)) and \(\text{HCl}\) (where \(C=\text{H}^+\), \(D=\text{Cl}^-\)) exchange ions: \(\text{Na}^+\) pairs with \(\text{Cl}^-\) to form \(\text{NaCl}\), and \(\text{H}^+\) pairs with \(\text{OH}^-\) to form \(\text{H}_2\text{O}\). This follows the double replacement pattern \(AB + CD
ightarrow AD + CB\).

Answer:

\(\text{NaOH} + \text{HCl}
ightarrow \text{NaCl} + \text{H}_2\text{O}\) (the fourth option)