Introduction
Nitric oxide (NO) is an important chemical compound that has various applications in industry, medicine and environmental science. It is formed by the oxidation of ammonia (NH3) in the presence of oxygen (O2). The reaction can be written as:
4��3+5�2→4��+6�2�4NH3+5O2→4NO+6H2O
This reaction is an example of a chemical kinetics problem, where we are interested in studying the rates of change of the reactants and products over time. One of the questions that we can ask is: how is the rate of formation of NO related to the rate of consumption of NH3?
Rate Law and Stoichiometry
To answer this question, we need to use two concepts: the rate law and the stoichiometry. The rate law is an expression that relates the rate of a reaction to the concentrations of the reactants and products. For example, for a general reaction:
��+��→��+��aA+bB→cC+dD
The rate law can be written as:
rate=�[�]�[�]�rate=k[A]m[B]n
where k is the rate constant, m and n are the orders of reaction with respect to A and B, respectively, and [A] and [B] are the concentrations of A and B, respectively. The values of k, m and n depend on the mechanism and conditions of the reaction.
The stoichiometry is the relationship between the amounts of reactants and products in a balanced chemical equation. For example, for the reaction above, we can write:
−�[�]��=���[�]��=���[�]��−dtd[A]=cadtd[C]=dadtd[D]
where −�[�]��−dtd[A] is the rate of consumption of A, �[�]��dtd[C] is the rate of formation of C, and �[�]��dtd[D] is the rate of formation of D. The coefficients a, b, c and d are the stoichiometric coefficients in the balanced equation.
Application to NO Formation
For the reaction of NH3 oxidation, we can apply these concepts to find the relationship between the rate of formation of NO and the rate of consumption of NH3. According to Toppr, we can write the rate law as:
rate=�[��3][�2]3/2rate=k[NH3][O2]3/2
where k is the rate constant, [NH3] is the concentration of NH3, and [O2] is the concentration of O2. According to Numerade, we can use the stoichiometry to write:
−�[��3]��=44�[��]��=�[��]��−dtd[NH3]=44dtd[NO]=dtd[NO]
where −�[��3]��−dtd[NH3] is the rate of consumption of NH3, and �[��]��dtd[NO] is the rate of formation of NO. The coefficients 4 and 4 are from the balanced equation.
Combining these two expressions, we get:
rate=�[��3][�2]3/2=−�[��3]��=�[��]��rate=k[NH3][O2]3/2=−dtd[NH3]=dtd[NO]
Therefore, we can conclude that the rate of formation of NO is equal to the rate of consumption of NH3 in this reaction.
Conclusion
In this article, we have explained how to use the rate law and the stoichiometry to find the relationship between the rates of formation and consumption in a chemical reaction. We have applied this method to the reaction of NH3 oxidation to NO, and found that the rate of formation of NO is equal to the rate of consumption of NH3 in this reaction. This means that for every mole of NH3 that is consumed, one mole of NO is formed. This information can be useful for designing reactors, controlling emissions, optimizing yields and understanding reaction mechanisms.
