Question

1. choose the best answer.

which of the following reactions shows that a catalyst has been added?
si + o₂ ↔ sio₂
h₂o₂ →pd h₂ + o₂
2li + o₂ → 2lio + energy
2ki →δ 2k + i₂

1. choose the best answer.

which of the following reactions represents a decomposition reaction?
cao + co₂ → caco₃
2mg + o₂ → 2mgo
2h₂ (g) + o₂ (g) → 2h₂o (g)
2h₂o₂ → 2h₂o + o₂

Explanation:

Question 6

A catalyst is written above or below the arrow in a chemical equation. In the reaction $\ce{H_{2}O_{2} \xrightarrow{\text{Pd}} H_{2} + O_{2}}$, Pd (palladium) is the catalyst as it is written above the arrow, indicating it speeds up the reaction without being consumed. The other reactions either show a reversible reaction, energy release, or heat (Δ) as a condition, not a catalyst.

A decomposition reaction is when a single compound breaks down into two or more simpler substances. The reaction $\ce{2H_{2}O_{2}
ightarrow 2H_{2}O + O_{2}}$ shows hydrogen peroxide breaking down into water and oxygen. The other reactions are combination reactions (two or more substances combining into one).

Answer:

$\boldsymbol{\ce{H_{2}O_{2} \xrightarrow{\text{Pd}} H_{2} + O_{2}}}$ (the second option: $\ce{H_{2}O_{2} \xrightarrow{\text{Pd}} H_{2} + O_{2}}$)

Question 7