12.1 Chemical Reaction Rates
2 min read•june 25, 2024
Chemical reactions happen at different speeds. Reaction rates measure how quickly reactants turn into products. Factors like temperature, concentration, and catalysts affect how fast reactions occur. Understanding rates helps predict and control chemical processes.
Rate expressions show how reaction speed relates to reactant amounts. They're built using balanced equations and experimental data. Interpreting rate data involves measuring concentration changes over time and using graphs to find rate constants and orders.
Chemical Reaction Rates
Concept of chemical reaction rate
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- Measures speed at which reactants convert into products
- Defined as change in concentration of reactants or products per unit time
- Expressed as or
- Influenced by factors like temperature (higher temp increases rate), concentration (higher conc of reactants increases rate), and catalysts (lower barrier)
- Defined as change in concentration of reactants or products per unit time
- Plays crucial role in
- Enables prediction of chemical system behavior (reaction progress over time)
- Optimizes industrial processes (maximizing yield and efficiency)
- Elucidates reaction mechanisms and rate-limiting steps (slowest step determines overall rate)
Construction of rate expressions
- Relate to reactant concentrations
- Derived from balanced chemical equation and experimentally determined
- Follows general form:
- : , temperature-dependent
- , : reactant concentrations
- , : reaction orders, determined experimentally
- Construction steps:
- Balance chemical equation
- Experimentally determine reaction orders for each reactant
- Substitute concentrations and reaction orders into general
- used to simplify complex rate expressions for reactions with intermediates
Interpretation of reaction rate data
- Determined by measuring change in reactant or product concentration over time
- Concentration measured using techniques like (absorbance) or (volume of titrant)
- Graphical methods for rate determination
- Concentration vs time plot
- Tangent line slope at any point gives
- ln(concentration) vs time plot for first-order reactions
- Straight line slope gives negative ()
- 1/concentration vs time plot for second-order reactions
- Straight line slope gives rate constant ()
- Concentration vs time plot
- Analyzing effect of changing conditions on rates
- Compare rates at different temperatures (), concentrations, or with catalysts
- Helps understand factors influencing reaction and determine rate law
Theoretical foundations of reaction rates
- explains how reactions occur through molecular collisions
- Emphasizes importance of collision frequency and orientation
- describes formation of activated complex during reaction
- details step-by-step pathway of chemical reaction
- concept used to measure time for concentration of reactant to decrease by half
Key Terms to Review (32)
Activation Energy: Activation energy is the minimum amount of energy required to initiate a chemical reaction. It represents the energy barrier that must be overcome for the reaction to occur, acting as a catalyst for the transformation of reactants into products.
Activation energy (Ea): Activation energy (Ea) is the minimum amount of energy required for a chemical reaction to occur. It determines the rate at which reactants transform into products.
Arrhenius equation: The Arrhenius equation describes the temperature dependence of reaction rates. It shows how the rate constant $k$ increases exponentially with an increase in temperature.
Arrhenius Equation: The Arrhenius equation is a mathematical formula that describes the relationship between the rate of a chemical reaction and the temperature at which the reaction occurs. It is a fundamental concept in the field of chemical kinetics and is widely used to understand and predict the behavior of chemical reactions.
Catalysis: Catalysis is the process by which a substance, called a catalyst, increases the rate of a chemical reaction without being consumed or altered itself. Catalysts work by providing an alternative pathway for the reaction, lowering the activation energy required and allowing the reaction to proceed more quickly.
Chemical Kinetics: Chemical kinetics is the study of the rates of chemical reactions and the factors that influence those rates. It examines the speed at which reactants are converted into products, providing insights into the mechanisms and pathways of chemical processes.
Collision theory: Collision theory explains how and why chemical reactions occur by describing the conditions under which reactant particles must collide. Effective collisions require proper orientation and sufficient energy to overcome activation energy.
Collision Theory: Collision theory is a model that explains how chemical reactions occur by describing the necessary conditions for reactant molecules to collide and form products. It is a fundamental concept in understanding the factors that affect the rates of chemical reactions.
First-Order Reaction: A first-order reaction is a chemical reaction where the rate of the reaction is directly proportional to the concentration of a single reactant. The reaction rate is independent of the concentrations of other reactants or products involved in the reaction.
Half-life: Half-life is the time required for half of the radioactive nuclei in a sample to decay. It is a characteristic property of each radioactive isotope.
Half-life: Half-life is the time it takes for a radioactive substance to decay to half of its original amount. It is a fundamental concept in nuclear chemistry that describes the exponential decay of radioactive isotopes and is crucial for understanding the behavior of radioactive materials.
Initial rate: The initial rate is the instantaneous rate of reaction at the very beginning when the reactants are first mixed. It is determined by measuring the change in concentration of a reactant or product over a short time period immediately after the reaction starts.
Instantaneous rate: The instantaneous rate is the rate of a chemical reaction at a specific moment in time. It is determined by taking the derivative of concentration with respect to time.
Integrated rate laws: Integrated rate laws describe the concentration of reactants as a function of time. They are derived from differential rate laws and are used to determine reaction order and rate constants.
Overall reaction order: Overall reaction order is the sum of the exponents of the concentration terms in a rate law equation. It indicates how the rate of reaction depends on the concentration of reactants.
Rate constant: The rate constant, often denoted as $k$, is a proportionality factor in the rate equation that relates the reaction rate to the concentration of reactants. Its value is specific to a particular reaction and changes with temperature.
Rate Constant: The rate constant is a measure of the speed or rate at which a chemical reaction occurs. It is a fundamental parameter that describes the intrinsic reactivity of the reactants and the reaction mechanism, and it is an essential component in understanding and predicting the kinetics of chemical processes.
Rate expression: A rate expression describes the rate of a chemical reaction in terms of the concentration of reactants. It shows how the rate depends on the concentrations of each reactant.
Rate Expression: The rate expression, also known as the rate law, is a mathematical equation that describes the relationship between the rate of a chemical reaction and the concentrations of the reactants involved. It provides a quantitative way to predict and understand the kinetics of a chemical process.
Rate Law: The rate law is an equation that describes the relationship between the rate of a chemical reaction and the concentrations of the reactants. It is a fundamental concept in chemical kinetics that helps quantify and predict the speed of a reaction under specific conditions.
Rate of reaction: The rate of reaction is the speed at which reactants are converted into products in a chemical reaction. It is typically measured as the change in concentration of reactants or products per unit time.
Rate-Limiting Step: The rate-limiting step is the slowest step in a multi-step chemical reaction that determines the overall rate of the reaction. It is the step that controls the speed at which the entire reaction proceeds, as the other steps cannot occur faster than this slowest step.
Reaction mechanism: A reaction mechanism describes the step-by-step sequence of elementary reactions by which overall chemical change occurs. It provides detailed information on the intermediates, transition states, and energy changes throughout the process.
Reaction Mechanism: A reaction mechanism is the step-by-step sequence of elementary reactions that describes how reactants are transformed into products during a chemical reaction. It provides a detailed understanding of the pathways and intermediates involved in the overall chemical process.
Reaction Order: Reaction order is a measure of how the rate of a chemical reaction changes with the concentrations of the reactants. It describes the relationship between the rate of a reaction and the concentrations of the reactants involved, providing insights into the mechanism of the reaction.
Reaction Rate: Reaction rate is the measure of the speed at which a chemical reaction occurs, quantifying the change in the concentration of reactants or products over time. It is a fundamental concept in understanding the dynamics of chemical processes and how they can be influenced and controlled.
Second-Order Reaction: A second-order reaction is a chemical reaction where the rate of the reaction is proportional to the square of the concentration of one of the reactants or to the product of the concentrations of two reactants. This type of reaction is important in understanding the kinetics and mechanisms of chemical processes.
Spectrophotometry: Spectrophotometry is an analytical technique that measures the amount of light absorbed by a sample at different wavelengths. It is widely used in various fields, including chemistry, to quantify the concentration of specific compounds in a solution.
Steady-State Approximation: The steady-state approximation is a mathematical technique used in chemical kinetics to simplify the analysis of complex reaction mechanisms. It assumes that the concentration of certain intermediate species in a reaction remains constant over time, allowing for the derivation of simplified rate equations.
Titration: Titration is a quantitative analytical technique used to determine the unknown concentration of a solution by gradually adding a measured volume of a standard solution with a known concentration until a specific endpoint is reached, indicating the completion of a chemical reaction. This process allows for the precise measurement and calculation of the concentration of the unknown solution.
Titration analysis: Titration analysis is a quantitative chemical technique used to determine the concentration of an unknown solution by reacting it with a solution of known concentration.
Transition State Theory: Transition state theory is a model that describes the mechanism of chemical reactions by focusing on the high-energy intermediate state that forms as reactants are transformed into products. This theory provides a framework for understanding the factors that influence the rate of a chemical reaction.