Question

Match the following: List I List II A \(\mathrm{NH}_{4} \mathrm{NO}_{2} \rightarrow \mathrm{N}_{2}+2 \mathrm{H}_{2} \mathrm{O}\) (p) Zero order B. \(\mathrm{H}_{2}+\mathrm{Cl}_{2} \rightarrow 2 \mathrm{HCl}\) (q) Ist order C. \(\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{4}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O} \rightarrow\) (r) Pseudo Ist order \(\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}(\mathrm{aq})+\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}(\mathrm{aq})\) D. \(2 \mathrm{HI} \rightarrow \mathrm{H}_{2}+\mathrm{I}_{2}\) (s) Photo chemical reaction

Short answer

A-Q, B-S, C-R, D can be reconstructed.

Step-by-step solution

Analyze Reaction A

Reaction A is \( \mathrm{NH}_{4} \mathrm{NO}_{2} \rightarrow \mathrm{N}_{2}+2 \mathrm{H}_{2} \mathrm{O} \). This is a thermal decomposition reaction and depends on temperature but not on the concentration of any reactant. Such reactions typically follow first-order kinetics.

Analyze Reaction B

Reaction B is \( \mathrm{H}_{2}+\mathrm{Cl}_{2} \rightarrow 2 \mathrm{HCl} \). This reaction is generally initiated by light (photons), making it a photochemical reaction.

Analyze Reaction C

Reaction C is \( \mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{4}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O} \rightarrow \mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}(\mathrm{aq})+\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}(\mathrm{aq}) \). This is a hydrolysis reaction in aqueous solution that follows pseudo first-order kinetics due to the large excess of water.

Analyze Reaction D

Reaction D is \( 2 \mathrm{HI} \rightarrow \mathrm{H}_{2}+\mathrm{I}_{2} \). This reaction is a typical second-order reaction based on its stoichiometry since it's bimolecular in \( \mathrm{HI} \), but the rate can resemble a variety of orders depending on conditions. In general treatment, it's differentiated from zero-order reactions.

Match Reactions to Orders

- A correlates to (q) 1st order. - B correlates to (s) Photo chemical reaction. - C correlates to (r) Pseudo 1st order. - D doesn't fit perfectly but typically would not be zero or pseudo-first excluding any modified scenarios.

Key concepts

First Order Reactions

First order reactions are chemical reactions where the rate is directly proportional to the concentration of one reactant. They are a cornerstone in the study of reaction kinetics. In simpler terms, if you double the concentration of the reactant, the reaction rate also doubles. The mathematical representation of a first-order reaction rate is given by:
\[\text{Rate} = k[A]\]where \(k\) is the rate constant and \([A]\) is the concentration of the reactant. This concept is usually encountered in processes such as radioactive decay or the decomposition of compounds.
A key characteristic of first order reactions is their constant half-life. The half-life is the time required for half of the reactant to convert into product. For a first-order reaction, the half-life is independent of the initial concentration and is calculated using the formula:
\[t_{1/2} = \frac{0.693}{k}\]Understanding first order reactions helps in predicting how long it will take for a reactant to reach a certain concentration, which is especially useful in fields like pharmacology and environmental science.

Photochemical Reactions

Photochemical reactions are processes that proceed through the absorption of light, typically in the ultraviolet or visible regions of the electromagnetic spectrum. These reactions are fundamentally important in nature and industry. For example, photosynthesis, where plants convert light energy into chemical energy, is a famous photochemical process.
The role of photons in such reactions cannot be overstated. They provide the necessary energy to break bonds in molecules, initiating chemical changes. An important aspect of photochemical reactions is that they can occur without substantial changes in temperature compared to thermal reactions.
In photochemical reactions, the rate does not depend on the concentration of reactants in the traditional sense. Instead, it is strongly influenced by the intensity and wavelength of the light source. The reaction between hydrogen and chlorine gas to produce hydrochloric acid (\(\mathrm{H}_{2} + \mathrm{Cl}_{2} \rightarrow 2 \mathrm{HCl}\)) exemplifies a classic photochemical reaction where light acts as the driving force for the reaction to occur.

Pseudo First Order

Pseudo first order reactions appear to follow first-order kinetics but are actually a simplification of more complex reactions. This generally occurs when one reactant is present in large excess compared to the other(s), making its concentration effectively constant during the reaction.
For instance, consider the hydrolysis reaction in an aqueous solution where water is present in large excess. Though the reaction actually depends on the concentrations of both the substrate and water, the enormous quantity of water means its concentration remains unchanged and can be ignored in the rate equation:
\[\text{Rate} = k'[A]\]This transformation simplifies the study of reaction kinetics because it allows us to treat the rate law as if it were a first-order reaction with a modified rate constant \(k'\).
Pseudo first order reactions are widely applicable in biochemistry and environmental chemistry for simplifying complex rate expressions, making experimental results easier to interpret. This principle can be seen in the hydrolysis of sucrose, where the water is in such excess that its concentration does not noticeably change over the course of the reaction.