Chemical kinetics usually referred to as reaction kinetics, is a discipline of physical chemistry concerned with the speeds of chemical reactions.
If the speed of a reaction is affected by changes in the environment, we can learn something about how the reaction occurs.
Kinetic studies are useful for understanding reactions and have applications in the real world. Reactions are carried out in reactors in industry, for example, where substances are mixed, heated and agitated for a brief time, and then transferred to the next stage of the process. It’s critical to know how long to hold a reaction at one stage before moving on to the next, to ensure that the previous reaction has been completed before moving on to the next. Many processes can be improved by understanding how reactions occur. If it is known that a specific intermediate is involved in a process, it may be preferable to avoid using circumstances (such as certain solvents) that are incompatible with that intermediate. Additionally, chemicals could be added to make specific steps in the reaction go more smoothly.
Kinetic studies are useful not only in industry but also in understanding biological processes, particularly enzyme-catalyzed reactions. They also work on environmental and atmospheric chemistry to better understand several challenges, such as the fate of prescription drugs in wastewater and the ozone cycle’s cascade of reactions.
Rate of Formations and Disappearances
The number of reactants in any chemical reaction reduces as the reaction progresses, while the amount of products grows. It’s important to remember that the rate of the overall reaction is determined by the rate at which reactants are consumed or products are generated.
When the concentrations of reactants and products are plotted against time on a graph, the rate of production of products and rate of disappearance of reactants may be simply estimated using the slope of the product and reactant curves. The reaction’s total rate may or may not be equal to the formation and disappearance rates.
(a) At time t = 0, the product concentration is zero.
(b) Both reactants and products are present at time t = 0.
The slope of the reactants curve is negative, while the slope of the product curve is positive, suggesting that the concentration of reactants and products decreases and increases, respectively.
Factors affecting reaction rate
Nature of the reactants
The rate of reaction varies based on the components involved. The reactions tend to be slower when covalent bonds are formed between molecules and when big molecules are created.
The nature and strength of bonds in reactant molecules have a big impact on how quickly they turn into products.
The physical state of reactants
The rate of change is highly influenced by the physical condition of a reactant, whether it is solid, liquid, or gas. To elaborate, if the reactants are in the same phase, such as in an aqueous solution, the thermal motion will bring them together. The reaction will be limited to the interface between the reactants if they are in different stages. The reaction occurs mostly at their point of contact; in the case of a liquid and a gas, at the liquid’s surface.
Surface Area of reactants
When two solids are combined, the particles on the surface participate in the reaction. Similarly, if we crush a solid into smaller pieces, there will be more particles near the surface. This indicates that collisions between these and reactant particles will most likely become more common. As a result, the reaction will happen faster.
When two or more reactants are in the same fluid phase, their particles collide more frequently than when they are both solid or in a heterogeneous mixture. Collisions between particles occur at the interface between phases in a heterogeneous medium. The number of collisions per unit time, as well as the reaction rate, are dramatically lowered when compared to the homogeneous scenario.
Pressure
In a gaseous reaction, increasing the pressure increases the number of collisions between reactants, resulting in a faster reaction rate. This is because a gas’s activity is related to its partial pressure. This is analogous to the impact of increasing a solution’s concentration.
In addition to the simple mass-action impact, pressure can affect the rate coefficients themselves. When an inert gas is added to a mixture of high-temperature gas-phase processes, the rate coefficients and products change; variations in this phenomenon are referred to as fall-off and chemical activation. These phenomena arise when exothermic or endothermic reactions occur faster than heat transmission, resulting in non-thermal energy distributions in the reacting molecules (non-Boltzmann distribution). Increasing the pressure reduces this impact by increasing the heat transfer rate between the interacting molecules and the rest of the system.
Pressure can impact condensed-phase rate coefficients, albeit high pressures are required for a discernible effect because ions and molecules are not highly compressible. Diamond anvils are frequently used to study this effect. A pressure jump approach can also be used to investigate the kinetics of a process. This entails rapidly changing pressure and measuring the time it takes to return to equilibrium.
Absorption of light
When one reactant molecule absorbs light of a sufficient wavelength and is promoted to an excited state, it can supply the activation energy for a chemical reaction. Photochemistry is the study of reactions that are triggered by light, with photosynthesis being one of the most well-known examples.
Kinetics vs. Thermodynamics
- Thermodynamics is a branch of study that investigates the events that result from the interaction of thermal and other kinds of energy (mechanical, chemical, electrical). Kinetics is a branch of theoretical mechanics that studies the rules of motion of metrical things under force. Kinetics investigates the connections between body movements and ICT-derived samples like strength and momentum.
- Thermodynamics is based on man’s experience with macroscopic bodies of similar dimensions, moderate density, and moderate temperatures. It is a discipline of physics that investigates energy, how it is converted into different forms, such as heat, and how it can be used to accomplish labour. Thermodynamics is the study of macroscopic systems having a large number of degrees of freedom.
- Kinetics is a branch of dynamics that investigates the effects of force on bodily movement. It includes mobility in a straight line and a circular motion along a curve (e.g., parabolic motion). Newton’s laws of motion and D’Alembert’s principle of kinetic equilibrium, or the same laws that are in line with the theory of relativity, are the principles of kinetics (in the region of high velocities, masses).
- Thermodynamics looks at whether a process (reaction) can happen, whereas kinetics looks at how fast it can happen.
- Thermodynamics demonstrates whether or not there is enough force to cause a transition. Kinetics demonstrates how to break through the energy barrier to finish the transition.
CONCLUSION
Chemical kinetics is a branch of physical chemistry concerned with determining the rates at which chemical processes occur. Thermodynamics, on the other hand, is concerned with the direction in which a process happens but not with the rate of the process. Chemical kinetics is the clock, while thermodynamics is the arrow of time. Chemical kinetics has far-reaching ramifications because it is related to many parts of cosmology, geology, biology, engineering, and even psychology. Chemical kinetics principles apply to purely physical processes and chemical reactions.