To determine which of the given equations represents a combustion reaction, we need to understand the defining characteristics of a combustion reaction. A combustion reaction typically involves a hydrocarbon reacting with oxygen to produce carbon dioxide and water. Let's examine each equation in detail.
### Reaction 1:
[tex]\[Ca + 2 HCl \longrightarrow CaCl_2 + H_2\][/tex]
In this reaction, calcium (Ca) reacts with hydrochloric acid (HCl) to form calcium chloride (CaCl_2) and hydrogen gas (H_2). This type of reaction is generally referred to as a single displacement reaction, not a combustion reaction.
### Reaction 2:
[tex]\[2 C_2H_6 + 7 O_2 \longrightarrow 4 CO_2 + 6 H_2O\][/tex]
In this equation, ethane (C_2H_6) reacts with oxygen (O_2) to produce carbon dioxide (CO_2) and water (H_2O). This reaction involves a hydrocarbon (ethane) reacting with oxygen and producing carbon dioxide and water, which fits the criteria for a combustion reaction.
Since a combustion reaction involves a hydrocarbon reacting with oxygen to produce carbon dioxide and water, the second equation represents a combustion reaction.
Therefore, the equation that represents a combustion reaction is:
[tex]\[2 C_2H_6 + 7 O_2 \longrightarrow 4 CO_2 + 6 H_2O\][/tex]
The correct answer is:
[tex]\[2\][/tex]
