Easy Chemistry: Rate Equations and Fun Experiments!

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Rishek M

31/03/2023

Chemistry

OCR year 13 - rates of reaction

Subjects

Chemistry

Physical chemistry

Rate equations (a-level only)

Easy Chemistry: Rate Equations and Fun Experiments!

Name: Knowunity
Brand: Knowunity

This document covers key concepts in chemical kinetics, focusing on rate equations, experimental analysis, and reaction mechanisms. It provides detailed explanations and methods for determining reaction orders, rate constants, and activation energies.

Overall Summary:

The document provides a comprehensive guide on rate equations and experimental analysis in chemistry, covering:

Rate equations and their components
Experimental methods for determining reaction orders
Analysis of concentration-time graphs
Calculation of rate constants
Half-life in first-order reactions
The Arrhenius equation and its applications
Rate-determining steps in reaction mechanisms

...

31/03/2023

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Page 2: Advanced Kinetics Concepts

This page delves into more advanced concepts in chemical kinetics.

Half-Life and First-Order Reactions

Definition: Half-life $t½$ is the time taken for the concentration of a reactant to halve.

First-order reactions have a constant half-life, which can be used to identify them.

Calculating Rate Constants from Concentration-Time Data

Two methods are presented:

Using the half-life formula: k = ln $2$ / t½
Using the gradient of a rate-concentration graph

Arrhenius Equation

Vocabulary: The Arrhenius equation relates the rate constant to temperature and activation energy.

The page provides the standard and logarithmic forms of the Arrhenius equation:

Standard form: k = Ae^ $-Ea/RT$
Logarithmic form: ln k = -Ea/RT + ln A

Methods for finding Ea $activation energy$ and A $pre-exponential factor$ are outlined.

Rate Mechanisms

Definition: The rate-determining step is the slowest step in a reaction mechanism.

An important rule is presented: The rate equation includes all reactants in and before the rate-determining step.

Highlight: The number of moles of a reactant in the rate-determining step equals its order in the rate equation.

The page concludes with graphical representations of zero-order, first-order, and second-order reactions, emphasizing the importance of understanding these graphs for kinetic analysis.

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Subjects

Chemistry

Physical chemistry

Rate equations (a-level only)

Chemistry

•

31 Mar 2023

•

2 pages

Easy Chemistry: Rate Equations and Fun Experiments!

Rishek M

@rishek.manta

Overall Summary:

The document provides a comprehensive... Show more

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Page 2: Advanced Kinetics Concepts

This page delves into more advanced concepts in chemical kinetics.

Half-Life and First-Order Reactions

Definition: Half-life $t½$ is the time taken for the concentration of a reactant to halve.

First-order reactions have a constant half-life, which can be used to identify them.

Calculating Rate Constants from Concentration-Time Data

Two methods are presented:

Using the half-life formula: k = ln $2$ / t½
Using the gradient of a rate-concentration graph

Arrhenius Equation

Vocabulary: The Arrhenius equation relates the rate constant to temperature and activation energy.

The page provides the standard and logarithmic forms of the Arrhenius equation:

Standard form: k = Ae^ $-Ea/RT$
Logarithmic form: ln k = -Ea/RT + ln A

Methods for finding Ea $activation energy$ and A $pre-exponential factor$ are outlined.

Rate Mechanisms

Definition: The rate-determining step is the slowest step in a reaction mechanism.

An important rule is presented: The rate equation includes all reactants in and before the rate-determining step.

Highlight: The number of moles of a reactant in the rate-determining step equals its order in the rate equation.

The page concludes with graphical representations of zero-order, first-order, and second-order reactions, emphasizing the importance of understanding these graphs for kinetic analysis.

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Improve your grades

Join milions of students

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Page 1: Rate Equations and Experimental Analysis

This page focuses on rate equations and experimental methods for determining reaction orders.

Definition: A rate equation expresses the rate of a reaction in terms of the concentrations of reactants and a rate constant.

The page outlines a model answer structure for analyzing experiments to determine reaction orders:

Compare experiments where only one reactant concentration changes.
Observe how the rate changes with concentration changes.
Determine the order of each reactant based on these observations.

Example: If doubling $A$ increases the rate by a factor of 4, the order with respect to A is 2.

The page also covers concentration-time graphs for different reaction orders:

Highlight: The shape of concentration-time graphs depends on the overall order of the reaction:

First order: exponential decay

Second order: reciprocal plot

Third order: more complex curve

Determining Rate Constants

The method for calculating rate constants is explained:

Rearrange the rate equation to solve for k.
Substitute values from one of the given experiments.

Example: For a rate equation Rate = k $A$ ² $B$ , rearrange to k = Rate / $[A]²[B]$ and substitute values.

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