A synthesis reaction, also known as a direct combination reaction, is one in which two or more reactants combine to form a single product. Typically, it follows the general form:
[tex]\[ A + B \rightarrow AB \][/tex]
Let's analyze each option to determine if it fits this criteria:
A. [tex]\( 2 \text{Li} + \text{CaCl}_2 \rightarrow 2 \text{LiCl} + \text{Ca} \)[/tex]
- Here, two reactants are forming two products. This is a single replacement reaction, not a synthesis reaction.
B. [tex]\( \text{S} + \text{O}_2 \rightarrow \text{SO}_2 \)[/tex]
- In this equation, sulfur ([tex]\(\text{S}\)[/tex]) and oxygen ([tex]\(\text{O}_2\)[/tex]) combine to form sulfur dioxide ([tex]\(\text{SO}_2\)[/tex]), a single product. This fits the definition of a synthesis reaction where two reactants combine to form a single product.
C. [tex]\( \text{CH}_4 + 2 \text{O}_2 \rightarrow 2 \text{H}_2\text{O} + \text{CO}_2 \)[/tex]
- This equation shows methane ([tex]\(\text{CH}_4\)[/tex]) and oxygen ([tex]\(\text{O}_2\)[/tex]) reacting to form water ([tex]\(\text{H}_2\text{O}\)[/tex]) and carbon dioxide ([tex]\(\text{CO}_2\)[/tex]). This reaction is an example of a combustion reaction, not a synthesis reaction.
D. [tex]\( \text{HNO}_3 + \text{KOH} \rightarrow \text{KNO}_3 + \text{H}_2\text{O} \)[/tex]
- Here, nitric acid ([tex]\(\text{HNO}_3\)[/tex]) and potassium hydroxide ([tex]\(\text{KOH}\)[/tex]) react to form potassium nitrate ([tex]\(\text{KNO}_3\)[/tex]) and water ([tex]\(\text{H}_2\text{O}\)[/tex]). This reaction is a neutralization reaction, not a synthesis reaction.
Given this analysis, the correct example of a synthesis reaction is:
B. [tex]\( \text{S} + \text{O}_2 \rightarrow \text{SO}_2 \)[/tex]
