Question

which of the following is a combustion reaction?
\\( \mathrm{c}_3\mathrm{h}_8 + 5\mathrm{o}_2 \
ightarrow 3\mathrm{co}_2 + 4\mathrm{h}_2\mathrm{o} \\)
\\( \mathrm{(nh_4)_2co_3} + \mathrm{cacl_2} \
ightarrow 2\mathrm{nh_4cl} + \mathrm{caco_3} \\)
\\( \mathrm{fe} + 2\mathrm{hcl} \
ightarrow \mathrm{fecl_2} + \mathrm{h_2} \\)
\\( 2\mathrm{h_2o_2} \
ightarrow 2\mathrm{h_2o} + \mathrm{o_2} \\)
which is a correctly balanced chemical equation?
\\( 2\mathrm{cucl_2} + 3\mathrm{al} \
ightarrow 3\mathrm{alcl_3} + 2\mathrm{cu} \\)
\\( \mathrm{cucl_2} + 2\mathrm{al} \
ightarrow 2\mathrm{alcl_3} + \mathrm{cu} \\)
\\( 3\mathrm{cucl_2} + 2\mathrm{al} \
ightarrow 2\mathrm{alcl_3} + 3\mathrm{cu} \\)
\\( 2\mathrm{cucl_2} + \mathrm{al} \
ightarrow \mathrm{alcl_3} + 2\mathrm{cu} \\)

Explanation:

First Question (Combustion Reaction)

Step1: Recall Combustion Reaction Definition

A combustion reaction is a reaction where a substance reacts with oxygen (\(O_2\)) to produce carbon dioxide (\(CO_2\)) and water (\(H_2O\)) (for hydrocarbon combustion), releasing energy.

Step2: Analyze Each Option

• Option 1: \(C_3H_8 + 5O_2

ightarrow 3CO_2 + 4H_2O\)
Propane (\(C_3H_8\)) reacts with \(O_2\) to form \(CO_2\) and \(H_2O\) – fits combustion.

• Option 2: \((NH_4)_2CO_3 + CaCl_2

ightarrow 2NH_4Cl + CaCO_3\)
Double displacement (ions swap), no \(O_2\) involved – not combustion.

• Option 3: \(Fe + 2HCl

ightarrow FeCl_2 + H_2\)
Single displacement (metal displaces \(H\) from acid), no \(O_2\) – not combustion.

• Option 4: \(2H_2O_2

ightarrow 2H_2O + O_2\)
Decomposition (one compound breaks down), no \(O_2\) as reactant – not combustion.

Second Question (Balanced Chemical Equation)

Step1: Recall Balancing Rules

Atoms of each element must be equal on both sides (reactants and products).

Step2: Analyze Each Option

• Option 1: \(2CuCl_2 + 3Al

ightarrow 3AlCl_3 + 2Cu\)

• Cu: \(2\) (left) vs \(2\) (right) – good.
• Al: \(3\) (left) vs \(3\) (right) – good.
• Cl: \(2\times2 = 4\) (left) vs \(3\times3 = 9\) (right) – unbalanced.
• Option 2: \(CuCl_2 + 2Al

ightarrow 2AlCl_3 + Cu\)

• Cu: \(1\) (left) vs \(1\) (right) – good.
• Al: \(2\) (left) vs \(2\) (right) – good.
• Cl: \(2\) (left) vs \(2\times3 = 6\) (right) – unbalanced.
• Option 3: \(3CuCl_2 + 2Al

ightarrow 2AlCl_3 + 3Cu\)

• Cu: \(3\) (left) vs \(3\) (right) – good.
• Al: \(2\) (left) vs \(2\) (right) – good.
• Cl: \(3\times2 = 6\) (left) vs \(2\times3 = 6\) (right) – balanced.
• Option 4: \(2CuCl_2 + Al

ightarrow AlCl_3 + 2Cu\)

• Cu: \(2\) (left) vs \(2\) (right) – good.
• Al: \(1\) (left) vs \(1\) (right) – good.
• Cl: \(2\times2 = 4\) (left) vs \(3\) (right) – unbalanced.

Answer:

First Question: A. \(C_3H_8 + 5O_2
ightarrow 3CO_2 + 4H_2O\)
Second Question: C. \(3CuCl_2 + 2Al
ightarrow 2AlCl_3 + 3Cu\)