Classifying the reaction type
The phrase “reaction between a metal and a nonmetal synthesis or decomposition” points to a common pattern in general chemistry: a metal and a nonmetal combine to form a single ionic compound. That pattern is a synthesis (combination) reaction, not a decomposition reaction.
Key idea: Synthesis builds a more complex substance from simpler reactants. Decomposition breaks a compound into simpler substances. A metal + nonmetal reaction most often produces one product (an ionic solid), matching synthesis.
General patterns (synthesis vs decomposition)
| Reaction type | General form | Typical chemistry meaning |
|---|---|---|
| Synthesis (combination) | \(\mathrm{A + B \rightarrow AB}\) | Two (or more) reactants form one product. |
| Decomposition | \(\mathrm{AB \rightarrow A + B}\) | One compound breaks into simpler substances (often needing heat, electricity, or light). |
Writing the correct product formula for a metal + nonmetal reaction
A metal forms a cation and a nonmetal forms an anion. The ionic formula is found by balancing charges to make a neutral compound. Consider a concrete example (typical for introductory synthesis reactions):
Assume magnesium reacts with chlorine gas to form magnesium chloride. Magnesium commonly forms \(\mathrm{Mg^{2+}}\) and chlorine forms \(\mathrm{Cl^-}\), so the neutral ionic formula is \(\mathrm{MgCl_2}\).
Balancing a representative synthesis equation
Chlorine exists as a diatomic element \(\mathrm{Cl_2}\). Start with the unbalanced skeleton equation and then balance atoms:
\[ \mathrm{Mg + Cl_2 \rightarrow MgCl_2} \]
Atom count check confirms balance: one Mg on each side and two Cl on each side. Therefore, this metal + nonmetal reaction is a synthesis reaction and is already balanced.
How the corresponding decomposition would look (reverse process)
Decomposition is the reverse pattern, where the ionic compound breaks apart into simpler substances (often by electrolysis for ionic solids):
\[ \mathrm{MgCl_2 \rightarrow Mg + Cl_2} \]
This equation shows one compound producing simpler substances, matching decomposition.
Visualization: synthesis vs decomposition map for metal–nonmetal chemistry
Summary for the keyword case
For a reaction between a metal and a nonmetal, the expected classification is synthesis because two elements combine to form one ionic compound. Decomposition applies when that ionic compound breaks into simpler substances, often requiring an external energy source.