Question

Identify the combination reaction in the following:
This question has multiple correct options
A. $N{H_3} + {\rm{ }}HCl{\rm{ }} \to N{H_4}Cl$
B. $NaCl{\rm{ }} + {\rm{ }}KOH \to {\rm{ }}NaOH{\rm{ }} + {\rm{ }}KCl$
C. $2CO{\rm{ + }}{O_2}\; \to 2C{O_2}$
D. $Cu{\left( {OH} \right)_2} \to CuO{\rm{ }} + {\rm{ }}{H_2}O$

Answer 1

Combination reaction refers to such reactions in which two or more than two elements or two or more than two compounds react and produce a single compound/ product. Another name for combination reaction is synthesis reaction. This name is given to the combination reaction because new products are synthesised in this reaction with the combination of different reactants.

Complete step by step solution
Since in combination reactions new bonds are formed. So a large amount of heat is released in this reaction and as a result combination reactions are exothermic reactions.
The general form of combination reaction is;
$X{\rm{ }} + {\rm{ }}Y{\rm{ }} \to {\rm{ }}XY$, where X and Y may be either elements or compounds and XY is the final product.
Some of the examples of combination reaction are;
A highly reactive metal i.e. Sodium (Na) combines with a non-metal i.e. chlorine to produce sodium chloride.
$2Na\left( s \right){\rm{ }} + {\rm{ }}C{l_2}{\rm{ }}\left( g \right){\rm{ }} \to 2NaCl{\rm{ }}\left( g \right)$
In this example two elements combine to form a compound. Similarly, one element and one compound may combine to form a new compound. For example, carbon monoxide reacts with oxygen to form a new compound called carbon dioxide.
$2CO{\rm{ }} + {\rm{ }}{O_2}{\rm{ }} \to 2C{O_2}$
Also, two compounds participate in a combination reaction to form a new compound. For example; ammonia reacts with hydrochloric acid to form ammonium chloride.
$N{H_3}{\rm{ }} + {\rm{ }}HCl{\rm{ }} \to {\rm{ }}N{H_4}Cl\;$
**Hence, options (A) and (C), are the correct options.

Note: **
Thus, the reaction in which two or more elements or compounds combine to form a new product with the release of energy in the form of heat is termed a combination reaction.