Question

For the reaction: ${H_2} + C{l_2}\xrightarrow{{sunlight}}2HCl$ the order of the reaction is:
A. $0$
B. $2$
C. $1$
D. $3$

Answer 1

At normal temperature and pressure, hydrogen chloride ( $HCl$ ) is a gas made up of the element’s hydrogen and chlorine. Hydrochloric acid is the name for a gas solution in water. The relationship between the rate of a chemical reaction and the concentration of the species involved is referred to as the order of reaction.

Complete answer:
The direct reaction of chlorine ( $C{l_2}$ ) gas with hydrogen ( ${H_2}$ ) gas can produce hydrogen chloride; the reaction is fast at temperatures above ${250^ \circ }C$ . The reaction is followed by heat evolution and appears to be increased by moisture, as described by the equation
${H_2} + C{l_2}\xrightarrow{{sunlight}}2HCl$
This reaction is a photochemical reaction. Because the order of all photochemical reactions is independent of the concentration of reactants, it is zero.
When light energy is absorbed by the molecules of a substance, a photochemical reaction is initiated.
A zero-order reaction is a chemical reaction in which the rate does not change as the concentration of the reactants changes. As a result, the rate constant of these reactions is always equal to that of the specific reactions (since the rate of these reactions is proportional to the zeroth power of reactants concentration)
Hence, the correct option is A. $0$ .

Note:
The number of species whose concentration directly impacts the rate of reaction is represented by reaction order. All the exponents of the concentration terms in the rate expression can be added to get the order of reaction.