Question

Which chemical equation correctly represents the decomposition reaction that takes place when ammonia breaks down to form hydrogen gas and nitrogen gas?
2 points
NH3 → N + H
2NH3 → N2 +3 H2
NH3 + H2 → N2
N2 + H2 → NH3

Answer 1

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★ What is meant by a decomposition reaction ?

A reaction in which a single reactant breaks/splits into two or more simpler products is called a decomposition reaction.

Now, let us look at each of the chemical equations (representing decomposition of ammonia) to find out the correct one :-

● Equation 1 :

$\bold{NH_3----)N+H}$

In this chemical equation, even though ammonia is decomposed, both nitrogen and hydrogen are represented as monatomic elements. Hence, this equation is invalid as both the elements (hydrogen & oxygen) are diatomic.

● Equation 2 :

$\bold{2NH_3----)N_2+3H_2}$

In this chemical equation, both hydrogen and oxygen are represented as diatomic elements and the equation is correctly balanced. Hence, this equation is the correct one and is valid.

● Equation 3 :

$\bold{NH_3+H_2----)N_2}$

In this reaction, ammonia and hydrogen combines to form nitrogen. This chemical equation is clearly invalid as it can never take place.

● Equation 4 :

$\bold{N_2+H_2----)NH_3}$

In this chemical equation, nitrogen and hydrogen combines to form ammonia. This reaction can take place but, it is a combination reaction. Hence, this is also invalid because it does not represent the decomposition of ammonia but shows the formation of ammonia (this chemical is equation is unbalanced also).

Hence, equation 2 is correct as it clearly represents the decomposition of ammonia.