Question

which of the following is a synthesis reaction? *
fe + cucl₂ → fecl₂ + cu
nh₄no₃ → n₂o + 2h₂o
so₂ + h₂o → h₂so₃
koh + hno₃ → kno₃ + h₂o
which of the following reactions below is a double replacement reaction? *
2kclo₃ → 2kcl + 3o₂
c₅h₁₂ + 8o₂ → 5co₂ + 6h₂o
4fe + 3o₂ → 2fe₂o₃
pb(no₃)₂ + 2ki → pbi₂ + 2kno₃

Explanation:

First Question (Synthesis Reaction)

Step1: Recall synthesis reaction

A synthesis reaction is when two or more substances combine to form a single product (A + B → AB).

Step2: Analyze each option

• Option 1: \( \text{Fe} + \text{CuCl}_2

ightarrow \text{FeCl}_2 + \text{Cu} \) – Single replacement (one element replaces another).

• Option 2: \( \text{NH}_4\text{NO}_3

ightarrow \text{N}_2\text{O} + 2\text{H}_2\text{O} \) – Decomposition (one compound breaks into multiple products).

• Option 3: \( \text{SO}_2 + \text{H}_2\text{O}

ightarrow \text{H}_2\text{SO}_3 \) – Two reactants (\( \text{SO}_2 \) and \( \text{H}_2\text{O} \)) combine to form one product (\( \text{H}_2\text{SO}_3 \)), fits synthesis.

• Option 4: \( \text{KOH} + \text{HNO}_3

ightarrow \text{KNO}_3 + \text{H}_2\text{O} \) – Double replacement (acid - base neutralization, ions swap).

Step1: Recall double replacement

Double replacement is when two compounds exchange ions: \( \text{AB} + \text{CD}
ightarrow \text{AD} + \text{CB} \).

Step2: Analyze each option

• Option 1: \( 2\text{KClO}_3

ightarrow 2\text{KCl} + 3\text{O}_2 \) – Decomposition (one compound breaks down).

• Option 2: \( \text{C}_5\text{H}_{12} + 8\text{O}_2

ightarrow 5\text{CO}_2 + 6\text{H}_2\text{O} \) – Combustion (organic + \( \text{O}_2 \) → \( \text{CO}_2 + \text{H}_2\text{O} \)).

• Option 3: \( 4\text{Fe} + 3\text{O}_2

ightarrow 2\text{Fe}_2\text{O}_3 \) – Synthesis (multiple reactants form one product).

• Option 4: \( \text{Pb(NO}_3\text{)}_2 + 2\text{KI}

ightarrow \text{PbI}_2 + 2\text{KNO}_3 \) – \( \text{Pb}^{2+} \) swaps with \( \text{K}^+ \), \( \text{NO}_3^- \) swaps with \( \text{I}^- \), fits double replacement.

Answer:

\( \boldsymbol{\text{SO}_2 + \text{H}_2\text{O}
ightarrow \text{H}_2\text{SO}_3} \) (the option with this reaction)

Second Question (Double Replacement Reaction)