Chemical Kinetics 01 | Rate of Reaction | Class 12th/CUET
NCERT Wallah・69 minutes read
The chapter on chemical kinetics delves into factors affecting reaction rates, including concentration, temperature, and nature of the reaction. It discusses the relationship between the rate of reaction and reactant concentration, the importance of understanding the rate constant, and the differences between single-step and multi-step reactions.
Insights
- Concentration, temperature, and nature of the reaction are key factors influencing the rate of a chemical reaction. Catalysts can either speed up or slow down reaction rates, and the rate constant (K) is crucial, remaining constant regardless of concentration changes.
- Molecularity is crucial in determining the order of a single-step reaction, referring to the number of molecules colliding simultaneously in one step. It is always a whole number with a positive value and cannot be defined for multi-step reactions. The order and molecularity are equal in elementary reactions, where the rate law equation involves the rates of change of reactants and products.
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Recent questions
What is chemical kinetics?
Chemical kinetics is the study of reaction rates.
How is the rate of a chemical reaction defined?
The rate of a chemical reaction is the product formed per unit time.
What factors affect the rate of reactions?
Factors affecting the rate of reactions include concentration, temperature, and nature of the reaction.
What is molecularity in reactions?
Molecularity refers to the number of molecules colliding simultaneously in one step.
How is the rate constant determined?
The rate constant is determined by dividing the rate by the reactant concentration raised to the power of the reaction order.
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Summary
00:00
Chemical Kinetics: Understanding Reaction Rates and Factors
- The chapter on chemical kinetics in NCERT Students' Platform is about to begin, focusing on the rate of chemical reactions.
- Chemical kinetics involves understanding the rate of chemical reactions, which is related to the speed of reactions.
- The chapter delves into factors affecting the rate of reactions and the concept of molecularity in reactions.
- Practice questions are essential for a detailed discussion on the topic.
- The chapter builds on the knowledge from thermodynamics, emphasizing the importance of understanding the rate of reactions.
- The rate of a chemical reaction is defined as the product formed per unit time.
- Concentration plays a crucial role in determining the rate of reaction, with the formula involving the amount of product formed or reactant used over time.
- The rate of reaction is always positive, reflecting the speed at which products are formed or reactants are consumed.
- The formula for calculating the rate involves the change in product or reactant concentration over time.
- Two methods of calculating the rate are discussed: average rate over a long duration and instantaneous rate at a specific moment.
17:09
Understanding Reaction Rates and Rate Laws
- Instantaneous rate is calculated at a specific instant, termed as the rate at that exact moment.
- Average rate is calculated over a period, determined by Mean Average Rate formula: ΔP/ΔT.
- Graphs are utilized to understand reactions, with reactants transforming into products over time.
- The gradual conversion of reactants into products is likened to financial spending habits.
- Reactant to product rate varies with reactant concentration, initially high then decreasing.
- Factors influencing reaction rate include reactant concentration, temperature, and nature of the reaction.
- Catalysts can either speed up or slow down reaction rates.
- Rate law expresses the relationship between reaction rate and reactant concentration.
- The rate law equation includes the rate constant, denoted as K, and the reaction order, represented by the power of reactant concentration.
- To determine the rate constant, divide the rate by the reactant concentration raised to the power of the reaction order.
33:30
Rate of Reaction Determined by Rate Constant
- Concentration of reactants does not affect the rate of reaction
- Rate depends on the concentration of reactants
- Rate constant (K) is crucial and depends on temperature and nature of reaction
- Rate constant remains constant regardless of concentration changes
- Unit of rate constant is mole per liter per second inverse
- Zero order reaction has a rate law of R = K * A
- First order reaction has a rate law of R = K * A^N
- Rate law is experimentally verified and does not correspond to stoichiometric coefficients
- Rate law is determined experimentally, and the order of reaction is calculated through experiments
- Rate law for a reaction like A + B -> C is R = K * A^x * B^y, where x and y are experimentally determined powers
51:40
Determining Order of Reaction in Chemistry
- Order of reaction is not always equal to the stoichiometric coefficients of reactants A and B in a reaction.
- The overall order of reaction is determined experimentally and may not always be equal to the stoichiometric coefficients.
- Calculating the order of reaction involves writing the rate law, finding the rate values at given concentrations, and using the values to determine the order of A and B.
- The rate constant in the rate law remains constant, and the concentration values are used to calculate the order of reaction.
- The order of reaction can be calculated in three ways: overall order, order with respect to a particular reactant, and order with respect to individual reactants.
- The order of reaction can be positive, negative, or fractional, and can be determined experimentally.
- Reactions can be single-step or multi-step, with multi-step reactions also known as complex reactions.
- Molecularity of a reaction is defined only for single-step reactions, where the stoichiometric coefficients of reactants determine the molecularity.
- Molecularity cannot be defined for multi-step reactions, as it is specific to single-step reactions.
- In single-step reactions, the order of reaction is equal to the molecularity, but in complex reactions, the order and molecularity may differ.
01:09:57
Molecularity and Order in Chemical Reactions
- Molecularity in a chemical reaction refers to the number of molecules colliding simultaneously in one step.
- The product in a chemical reaction is formed when reactants collide, necessitating a collision for the reaction to occur.
- Molecularity can be one, two, three, or four, with the maximum being three due to the limitation of molecules touching each other.
- Molecularity is always a whole number with a positive value, and it is crucial in determining the order of a reaction.
- For a single-step reaction, the order of the reaction is equal to the molecularity.
- In an elementary reaction, the molecularity is determined by the stoichiometric coefficients of the individual reactants.
- The order and molecularity of elementary steps in a reaction are numerically equal.
- The rate law equation for an elementary reaction involves the rates of change of the reactants and products.
- Differential rate law equations for elementary reactions can be calculated based on the stoichiometry of the reaction.
- The unit of rate constant in a reaction depends on the order of the reaction, with different expressions for different orders.
01:28:00
Rate of Reaction Factors and Analysis
- The power of mole and liter is zero, making second inverse the unit rate. When dealing with reactions, the rate depends on temperature, not pressure or the nature of the reaction. The extent of the reaction and the concentration of the reactant are crucial factors to consider.
- In determining the rate of reaction related to a specific product, the relationship between bromine and bromide ions is essential. By carefully analyzing the options, the correct answer can be deduced by considering the given chemical equation and the specific rates of change.
