Question

1. choose the best answer. which of the following reactions shows that a catalyst has been added? \\(\ce{si + o_{2} -> sio_{2}}\\) \\(\ce{h_{2}o_{2} ->pt h_{2} + o_{2}}\\) \\(\ce{2li + o_{2} -> 2lio + energy}\\) \\(\ce{2ki ->\delta 2k + i_{2}}\\) 7) choose the best answer. which of the following reactions represents a decomposition reaction? \\(\ce{2h_{2}o_{2} -> 2h_{2}o + o_{2}}\\) \\(\ce{cao + co_{2} -> caco_{3}}\\) \\(\ce{2mg + o_{2} -> 2mgo}\\) \\(\ce{2h_{2}(g) + o_{2}(g) -> 2h_{2}o(g)}\\)

Explanation:

For question 6:

A catalyst is written above/below the reaction arrow, not as a reactant/product. $\text{Pt}$ (platinum) is shown above the arrow in the reaction of $\text{H}_2\text{O}_2$, meaning it acts as a catalyst. Other options have substances as reactants/products, not catalysts.

For question 7:

A decomposition reaction has one reactant breaking into multiple products. Only $2\text{H}_2\text{O}_2
ightarrow 2\text{H}_2\text{O} + \text{O}_2$ fits this (one reactant, two products). The others are combination reactions (two reactants forming one product).

Answer:

1. $\boldsymbol{\text{O } \text{H}_2\text{O}_2 \xrightarrow{\text{Pt}} \text{H}_2 + \text{O}_2}$
2. $\boldsymbol{\text{O } 2\text{H}_2\text{O}_2

ightarrow 2\text{H}_2\text{O} + \text{O}_2}$