The rate law for the decomposition of hydrogen iodide is - = d[HI]/dt = k[HI]2. The units of rate constant k are:
The rate law for the decomposition of hydrogen iodide is - = d[HI]/dt = k[HI]2. The units of rate constant k are:
L mol-1 s-1
L-1 mol s-1
L2 mol-2 s-1
L1/2 mol1/2 s-1
The Correct Option is A
Solution and Explanation
The correct option is: (A): L mol-1 s-1
The given rate law is −dtd[HI]=k[HI]2, where k is the rate constant and [HI] represents the concentration of hydrogen iodide. The units of the rate constant k can be determined by analyzing the units on both sides of the equation.
On the left side of the rate law, d[HI] represents the rate of change of concentration with respect to time, which has units of L⋅smol (moles per liter per second) as it's a change in concentration over time.
On the right side of the equation, 2[HI]2 represents the square of the concentration of hydrogen iodide, which has units of 2(Lmol)2 (moles per liter squared).
In order for both sides of the equation to have the same units, the units of the rate constant k must be such that when multiplied by 2[HI]2, it results in the units of the left side (L⋅smol).
Hence, the units of the rate constant k are L⋅smol, which is represented as L mol−1 s−1L mol−1 s−1.
This justification confirms that the answer "L mol-1 s-1" is appropriate for the units of the rate constant k.
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Concepts Used:
Chemical Kinetics
Chemical kinetics is the description of the rate of a chemical reaction. This is the rate at which the reactants are transformed into products. This may take place by abiotic or by biological systems, such as microbial metabolism.
Rate of a Chemical Reaction:
The speed of a reaction or the rate of a reaction can be defined as the change in concentration of a reactant or product in unit time. To be more specific, it can be expressed in terms of: (i) the rate of decrease in the concentration of any one of the reactants, or (ii) the rate of increase in concentration of any one of the products. Consider a hypothetical reaction, assuming that the volume of the system remains constant. R → P
Read More: Chemical Kinetics MCQ
Factors Affecting The Reaction Rate:
- The concentration of Reactants - According to collision theory, which is discussed later, reactant molecules collide with each other to form products.
- Nature of the Reactants - The reaction rate also depends on the types of substances that are reacting.
- Physical State of Reactants - The physical state of a reactant whether it is solid, liquid, or gas can greatly affect the rate of change.
- Surface Area of Reactants - When two or more reactants are in the same phase of fluid, their particles collide more often than when either or both are in the solid phase or when they are in a heterogeneous mixture. In a heterogeneous medium, the collision between the particles occurs at an interface between phases. Compared to the homogeneous case, the number of collisions between reactants per unit time is significantly reduced, and so is the reaction rate.
- Temperature - If the temperature is increased, the number of collisions between reactant molecules per second. Increases, thereby increasing the rate of the reaction.
- Effect Of Solvent - The nature of the solvent also depends on the reaction rate of the solute particles.
- Catalyst - Catalysts alter the rate of the reaction by changing the reaction mechanism.