Question

question 1
select all the combustion reactions.
□ fe + o₂ --> co₂ + h₂o
□ c₃h₈ + 5 o₂ --> 3co₂ + 4h₂o
□ 25 o₂ + 2c₈h₁₈ --> 18h₂o + 16co₂
□ ca(oh)₂ + 2hcl --> cacl₂ + h₂o
□ 2c₈h₁₈ + 25 o₂ --> 16co₂ + 18h₂o

Explanation:

Step1: Recall Combustion Reaction Definition

A combustion reaction is a reaction where a substance (usually a hydrocarbon) reacts with oxygen (\(O_2\)) to produce carbon dioxide (\(CO_2\)) and water (\(H_2O\)), often with heat and light.

Step2: Analyze Each Reaction

• **Reaction 1: \(Fe + O_2

ightarrow CO_2 + H_2O\)**
Reactant is iron (\(Fe\)), not a hydrocarbon. Products have \(CO_2\) and \(H_2O\), but reactant is incorrect for combustion. Not a combustion reaction.

• **Reaction 2: \(C_3H_8 + 5O_2

ightarrow 3CO_2 + 4H_2O\)**
Reactant \(C_3H_8\) (propane, a hydrocarbon) reacts with \(O_2\) to form \(CO_2\) and \(H_2O\). Matches combustion definition.

• **Reaction 3: \(25O_2 + 2C_8H_{18}

ightarrow 18H_2O + 16CO_2\)**
Reactant \(C_8H_{18}\) (octane, a hydrocarbon) reacts with \(O_2\) to form \(CO_2\) and \(H_2O\). Matches combustion definition (note: equation is balanced as \(2C_8H_{18} + 25O_2
ightarrow 16CO_2 + 18H_2O\), order of reactants/products doesn’t matter).

• **Reaction 4: \(Ca(OH)_2 + 2HCl

ightarrow CaCl_2 + H_2O\)**
Acid-base neutralization (hydroxide + acid → salt + water). No \(O_2\) or hydrocarbon. Not combustion.

• **Reaction 5: \(2C_8H_{18} + 25O_2

ightarrow 16CO_2 + 18H_2O\)**
Hydrocarbon (\(C_8H_{18}\)) reacts with \(O_2\) to form \(CO_2\) and \(H_2O\). Balanced and matches combustion definition.

Answer:

• \( \boldsymbol{C_3H_8 + 5 O_2

ightarrow 3CO_2 + 4H_2O} \)

• \( \boldsymbol{25 O_2 + 2C_8H_{18}

ightarrow 18H_2O + 16CO_2} \) (or \(2C_8H_{18} + 25 O_2
ightarrow 16CO_2 + 18H_2O\))

• \( \boldsymbol{2C_8H_{18} + 25 O_2

ightarrow 16CO_2 + 18H_2O} \)