Classify the sentences based on the chemical reactions they describe.

Synthesis Decomposition Replacement

When a clam shell $\left( CaCO _3\right)$ is heated, carbon dioxide $\left( CO _2\right)$ is given off and a white powder, calcium oxide (CaO), forms. Nitrogen pentoxide $\left( N _2 O _5\right)$ is an unstable gas that changes to nitrogen dioxide $\left( NO _2\right)$ and oxygen $\left( O _2\right)$ at room temperature. Sodium (Na) reacts with chlorine (Cl) to give sodium chloride (NaCl).

Zinc (Zn) metal reacts with copper sulfate $\left( Cu _2 SO _4\right)$ to give zinc sulfate $\left( ZnSO _4\right)$ and copper (Cu). A strip of magnesium (Mg) burns brightly in oxygen $\left( O _2\right)$ to form a white powder, magnesium oxide (MgO). On heating iron ore $\left( Fe _2 O _3\right)$ with carbon (C), we get iron (Fe) and carbon dioxide $\left( CO _2\right)$.

Question

03-11-2026
Chemistry

Answered

Classify the sentences based on the chemical reactions they describe.

Synthesis Decomposition Replacement

When a clam shell $\left( CaCO _3\right)$ is heated, carbon dioxide $\left( CO _2\right)$ is given off and a white powder, calcium oxide (CaO), forms. Nitrogen pentoxide $\left( N _2 O _5\right)$ is an unstable gas that changes to nitrogen dioxide $\left( NO _2\right)$ and oxygen $\left( O _2\right)$ at room temperature. Sodium (Na) reacts with chlorine (Cl) to give sodium chloride (NaCl).

Zinc (Zn) metal reacts with copper sulfate $\left( Cu _2 SO _4\right)$ to give zinc sulfate $\left( ZnSO _4\right)$ and copper (Cu). A strip of magnesium (Mg) burns brightly in oxygen $\left( O _2\right)$ to form a white powder, magnesium oxide (MgO). On heating iron ore $\left( Fe _2 O _3\right)$ with carbon (C), we get iron (Fe) and carbon dioxide $\left( CO _2\right)$.

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GinnyAnswer GinnyAnswer · Answer 1 · 2026-11-03T18:58:31-05:00

Synthesis reactions involve multiple reactants combining into one product, such as the formation of NaCl or MgO.
Decomposition reactions involve one reactant breaking down into multiple products, as seen when heating $CaCO_3$ or when $N_2O_5$ breaks down.
Replacement reactions involve elements trading places, illustrated by the reaction of Zn with $Cu_2SO_4$ or the reduction of iron ore ($Fe_2O_3$) with carbon.
The final classification correctly sorts each of the six sentences into its appropriate category based on chemical reaction definitions.

Explanation

Analysis and Classification of Chemical Reactions

To classify the given chemical reactions, we must analyze the number of reactants and products for each reaction and observe the nature of the chemical change described.

Definitions:

Synthesis: Two or more reactants combine to form a single product ($A + B \rightarrow AB$).
Decomposition: A single reactant breaks down into two or more simpler products ($AB \rightarrow A + B$).
Replacement: One or more elements in a compound are replaced by other elements ($AB + C \rightarrow AC + B$ or $AB + CD \rightarrow AD + CB$).

Let's evaluate each sentence:

"When a clam shell ($CaCO_3$) is heated, carbon dioxide ($CO_2$) is given off and a white powder, calcium oxide (CaO), forms."

Reactant: $CaCO_3$ (1)
Products: $CO_2$, $CaO$ (2)
Classification: Decomposition.

"Nitrogen pentoxide ($N_2O_5$) is an unstable gas that changes to nitrogen dioxide ($NO_2$) and oxygen ($O_2$) at room temperature."

Reactant: $N_2O_5$ (1)
Products: $NO_2$, $O_2$ (2)
Classification: Decomposition.

"Sodium (Na) reacts with chlorine (Cl) to give sodium chloride (NaCl)."

Reactants: Na, Cl (2)
Product: NaCl (1)
Classification: Synthesis.

"Zinc (Zn) metal reacts with copper sulfate ($Cu_2SO_4$) to give zinc sulfate ($ZnSO_4$)."

Reactants: Zn, $Cu_2SO_4$ (2)
Products: $ZnSO_4$, Cu (2)
Classification: Replacement.

"A strip of magnesium (Mg) burns brightly in oxygen ($O_2$) to form a white powder, magnesium oxide (MgO)."

Reactants: Mg, $O_2$ (2)
Product: MgO (1)
Classification: Synthesis.

"On heating iron ore ($Fe_2O_3$) with carbon (C), we get iron (Fe) and carbon dioxide ($CO_2$)."

Reactants: $Fe_2O_3$, C (2)
Products: Fe, $CO_2$ (2)
Classification: Replacement.

Organizing the Results

We can now organize our findings into the required classification table based on the analysis performed in the previous step.

Synthesis:
Sodium (Na) reacts with chlorine (Cl) to give sodium chloride (NaCl).
A strip of magnesium (Mg) burns brightly in oxygen ($O_2$) to form a white powder, magnesium oxide (MgO).

Decomposition:
When a clam shell ($CaCO_3$) is heated, carbon dioxide ($CO_2$) is given off and a white powder, calcium oxide (CaO), forms.
Nitrogen pentoxide ($N_2O_5$) is an unstable gas that changes to nitrogen dioxide ($NO_2$) and oxygen ($O_2$) at room temperature.

Replacement:
Zinc (Zn) metal reacts with copper sulfate ($Cu_2SO_4$) to give zinc sulfate ($ZnSO_4$).
On heating iron ore ($Fe_2O_3$) with carbon (C), we get iron (Fe) and carbon dioxide ($CO_2$).

Examples

Chemical reactions are all around us! For instance, when we bake, the decomposition of baking powder releases carbon dioxide, making our cakes rise. Conversely, the synthesis of water in fuel cells provides clean energy, and single replacement reactions are crucial in electroplating metals to prevent corrosion or to improve their appearance. Understanding these categories allows us to predict how substances will behave and interact in both industrial and everyday contexts.

Synthesis	Decomposition	Replacement

When a clam shell $\left( CaCO _3\right)$ is heated, carbon dioxide $\left( CO _2\right)$ is given off and a white powder, calcium oxide (CaO), forms.	Nitrogen pentoxide $\left( N _2 O _5\right)$ is an unstable gas that changes to nitrogen dioxide $\left( NO _2\right)$ and oxygen $\left( O _2\right)$ at room temperature.	Sodium (Na) reacts with chlorine (Cl) to give sodium chloride (NaCl).
Zinc (Zn) metal reacts with copper sulfate $\left( Cu _2 SO _4\right)$ to give zinc sulfate $\left( ZnSO _4\right)$ and copper (Cu).	A strip of magnesium (Mg) burns brightly in oxygen $\left( O _2\right)$ to form a white powder, magnesium oxide (MgO).	On heating iron ore $\left( Fe _2 O _3\right)$ with carbon (C), we get iron (Fe) and carbon dioxide $\left( CO _2\right)$.