For the reaction: \(\mathrm{A}_{2}(\mathrm{~g}) \rightarrow \mathrm{B}(\mathrm{g})+\frac{1}{2} \mathrm{C}(\mathrm{g})\) pressure of the system increases from 100 to \(120 \mathrm{~mm}\) in 5 min. The average rate of disappearance of \(\mathrm{A}_{2}\) (in \(\mathrm{mm} / \mathrm{min}\) ) in this time interval is (a) 4 (b) 8 (c) 2 (d) 16

Understanding reaction kinetics is essential when studying how reactions occur and at what rates they progress. Reaction kinetics, often simply called kinetics, looks into the factors that affect the speed of a chemical reaction and establishes the relationship between the reactivity of molecules and the rate at which a reaction proceeds.

Some of the main aspects of kinetics encompass the energy needed for reactions to occur, known as the activation energy, the orientation of reactant molecules when they collide, and the frequency of collisions. Factors like temperature, pressure, concentration of reactants, and the presence of catalysts are pivotal as they influence these aspects and thereby manipulate how fast a reaction can go from starting reactants to final products. A fundamental understanding of kinetics not only aids in predicting reaction rates but also in controlling processes in industries like pharmaceuticals and biochemical engineering.

When we talk about the average rate of reaction, we're measuring how quickly reactants turn into products over a period of time. It's an indicator of the speed of a chemical reaction. Remember, for the disappearance of a reactant, we often use a negative sign because the quantity of reactant is diminishing.

By following the formula Average rate = - (Change in concentration of A2) / (Change in time), it becomes clearer that if the concentration of a reactant decreases rapidly, the reaction rate is high. Conversely, very gradual declines in reactant concentration indicate a slower reaction. This concept is instrumental in the field of chemistry, as it helps predict the time needed for a reaction to reach completion, which is crucial for planning and optimizing chemical production.

In the context of gases, pressure plays a significant role and is directly related to the concentration of gas molecules. According to the ideal gas law, pressure is directly proportional to the number of molecules in a given volume at a constant temperature. This implies that an increase in pressure results from an increase in the number of gas molecules - suggesting a higher concentration.

As pressure changes, it can affect the rate of a reaction by altering the concentration of the gaseous reactant or product involved. More molecules in the same volume mean that they are more likely to collide with energy greater than the activation energy, a requirement for successful reactions. Understanding this relationship is vital when controlling reaction conditions, particularly in reactions involving gases where pressure can be a more convenient measure of concentration than molarity, especially on an industrial scale.