Question

Which reaction is an example of a synthesis reaction?
Responses

Cl2 + 2NaBr→ Br2 + 2NaCl 
uppercase C lowercase l subscript 2 end subscript plus 2 uppercase N lowercase a uppercase B lowercase r rightwards arrow uppercase B lowercase r subscript 2 end subscript plus 2 uppercase N lowercase a uppercase C lowercase l

2Na + 2H2O→2NaOH + H2
2 uppercase N lowercase a plus 2 uppercase H subscript 2 end subscript uppercase O rightwards arrow 2 uppercase N lowercase a uppercase O H plus uppercase H subscript 2 end subscript

2H2+O2→2H2O
2 uppercase H subscript 2 end subscript plus uppercase O subscript 2 end subscript rightwards arrow 2 uppercase H subscript 2 end subscript uppercase O

C7H16+11O2→7CO2+8H2O

Answer 1

The synthesis reaction is:
2H2 + O2 → 2H2O

Reason: a synthesis (combination) reaction has two or more reactants forming a single product. The others are not synthesis:
- Cl2 + 2NaBr → Br2 + 2NaCl is a single-displacement (halogen swap),
- 2Na + 2H2O → 2NaOH + H2 is a single-displacement (metal displacing hydrogen),
- C7H16 + 11O2 → 7CO2 + 8H2O is combustion.