Concept:The reaction between hydrogen and chlorine gas in the presence of sunlight is a classic photochemical reaction.
Formula:$$ \text{Rate} = k[\text{H}_2]^0[\text{Cl}_2]^0 = k $$
Solution:- This specific reaction is initiated and entirely driven by the absorption of photons from light, not by thermal molecular collisions based on concentration.
- Because changing the concentration of \( \text{H}_2 \) or \( \text{Cl}_2 \) does not change the amount of light absorbed, the reaction rate remains constant.
- Thus, it is independent of reactant concentration, making it a zero-order reaction.
Why other options are incorrect:Looking at the stoichiometry, one might incorrectly guess second order (1+1). However, photochemical kinetics overrule stoichiometry.
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