Question

25 multiple choice 1 point
which reaction is an example of a single replacement reaction?
○ na₂s + hcl → nacl + h₂s
○ 2na + fecl₂ → 2nacl + fe
○ al₂o₃ → al + o₂
○ c(s) + o₂(g) → co₂
clear my selection
26 multiple choice 1 point
what is the general formula for a decomposition reaction?
○ a + bx → b + ax
○ a + b → ab
○ cd → c + d
○ organic compound + o₂ → co₂ + h₂o
clear my selection

Explanation:

Question 25

Step1: Recall single replacement reaction

A single replacement reaction follows the pattern \( A + BX
ightarrow AX + B \), where a more reactive element replaces a less reactive element in a compound.

Step2: Analyze each option

• Option 1: \( \ce{Na_{2}S + HCl

ightarrow NaCl + H_{2}S} \) is a double replacement (metathesis) reaction (ions exchange: \( \ce{Na^+} \) with \( \ce{H^+} \), \( \ce{S^{2-}} \) with \( \ce{Cl^-} \)).

• Option 2: \( \ce{2Na + FeCl_{2}

ightarrow 2NaCl + Fe} \) follows \( A + BX
ightarrow AX + B \) (Na replaces Fe in \( \ce{FeCl_{2}} \)), so it's single replacement.

• Option 3: \( \ce{Al_{2}O_{3}

ightarrow Al + O_{2}} \) is a decomposition reaction (compound breaks into simpler substances).

• Option 4: \( \ce{C(s) + O_{2}(g)

ightarrow CO_{2}} \) is a combination (synthesis) reaction (elements combine to form a compound).

• Recall reaction types:
• Single replacement: \( A + BX

ightarrow B + AX \) (matches first option, but it's single replacement, not decomposition).

• Combination (synthesis): \( A + B

ightarrow AB \) (second option, not decomposition).

• Decomposition: A compound breaks into two or more simpler substances, so \( CD

ightarrow C + D \) (third option).

• Combustion of organic compounds: \( \text{Organic compound} + \ce{O_{2}}

ightarrow \ce{CO_{2}} + \ce{H_{2}O} \) (fourth option, combustion, not decomposition).

Answer:

\( 2\ce{Na} + \ce{FeCl_{2}}
ightarrow 2\ce{NaCl} + \ce{Fe} \) (the second option)

Question 26