Reaction Pathway Diagrams

A reaction pathway diagram is a graph that shows energy changes during a chemical reaction, helping to identify whether energy is released or energy is absorbed.

What are reaction pathway diagrams?

A reaction pathway diagram is a graph that shows how energy changes during a chemical reaction.
The diagram has:
- Y-axis: Energy level
- X-axis: Progress of reaction
They compare the energy of reactants and products.
It helps to identify whether a reaction is exothermic or endothermic.

Exothermic reactions

Exo- means out, so an exothermic reaction releases energy into the surroundings (usually as heat/light).
- This means products have less energy than reactants.
The diagram shows:
- A decrease in energy from the start to the end of the reaction
- A downward arrow labelled “Energy released”
Examples:
- Burning fuels (combustion), neutralisation, respiration

Endothermic reactions

Endo- means in, so an endothermic reaction absorbs energy from the surroundings.
- This means products have more energy than the reactants.
The diagram shows:
- An increase in energy from the start to the end of the reaction
- An upward arrow labelled “Energy absorbed”
Examples:
- Melting ice, photosynthesis

Key parts of the diagram

Reactants: The starting substances in a reaction.
- Their energy is shown at the beginning of the curve.
Products: The substances formed at the end of the reaction.
- Their energy is shown at the end of the curve.
Activation Energy: The 'hump' or 'peak' of the curve.
Enthalpy Change (ΔH): The overall energy change in the reaction
Reaction pathway diagrams help us visualise energy changes.

Reaction Pathway Diagrams 2

Reaction pathway diagrams show activation energy, enthalpy change, and the balance between bond breaking and bond making to determine whether a reaction is exothermic or endothermic.

Illustrative background for Activation energy (*E<sub>a</sub>*)

Illustrative background for Activation energy (*E<sub>a</sub>*) ?? "content

Activation energy (E_a)

Activation energy (E_a) is the minimum energy that reacting particles must have for a reaction to occur.
- This is shown as the 'hump' or 'peak' on the reaction pathway diagram.
This energy is required to break the initial bonds in the reactants before new bonds can form.
A high activation energy means a reaction is slower, as more energy is needed to start it.

Enthalpy change (ΔH)

ΔH is the difference in energy between the products and the reactants.
In an exothermic reaction:
- The products have a lower energy level than the reactants.
- The diagram shows a decrease in energy.
- The enthalpy change (ΔH) is negative.
In an endothermic reaction:
- The products have a higher energy level than the reactants.
- The diagram shows an increase in energy.
- The enthalpy change (ΔH) is positive.

Bond breaking & making

Breaking bonds in the reactants requires energy → endothermic process.
Making bonds in the products releases energy → exothermic process.

Bond breaking & making 2

The overall enthalpy change (ΔH) is calculated using bond energies:
- ΔH = (Energy absorbed to break bonds) - (Energy released to make bonds)
If more energy is released than absorbed → exothermic (ΔH is negative).
If more energy is absorbed than released → endothermic (ΔH is positive).

1States of Matter

1.1Solids, Liquids, & Gases

1.1.1States of Matter - Solids, Liquids & Gases

1.1.2Structure of Solids, Liquids & Gases

1.1.3Changes of State

1.1.4The Effects of Temperature & Pressure

1.1.5Kinetic Theory

1.1.6Kinetic Theory - Effects of Temperature & Pressure

1.2Diffusion

1.2.1Diffusion

1.2.2The Effect of Relative Molecular Mass

2Atoms, Elements & Compounds

2.1Elements, Compounds & Mixtures

2.1.1Differences Between Elements, Compounds & Mixtures

2.2Atomic Structure & the Periodic Table

2.2.1The Structure of the Atom

2.2.2Relative Charge, Mass & Atomic Numbers

2.2.3Electronic Configuration of Elements

2.3Isotopes

2.3.1Isotopes

2.3.2Electronic Configuration of Isotopes

2.3.3Calculating Relative Atomic Mass

2.4Ions & Ionic Bonds

2.4.1Properties of Ionic Compounds - Structure & Bond

2.4.2Formation of Ions & Ionic Bonds

2.4.3Formation of Ionic Bonds - Metals & Non-Metals

2.4.4Ionic Bonds

2.4.5Ionic Compounds

2.4.6Giant Lattice Structure of Ionic Compounds

2.5Simple Molecules & Covalent Bonds

2.5.1Covalent Bonds

2.5.2Formation of Covalent Bonds

2.5.3Structure & Properties of Simple Molecules

2.5.4Covalent Bonds in Simple Molecules

2.5.5Properties of Simple Molecular Compounds

2.6Giant Covalent Structures

2.6.1Giant Covalent Structures - Graphite

2.6.2Giant Covalent Structures - Diamond

2.6.3Uses of Graphite & Diamonds

2.6.4Giant Covalent Structures - Silicon Oxide

2.6.5Similarity Between Diamond & Silicon Oxide

2.7Metallic Bonding

2.7.1Metallic Bonding

2.7.2The Properties of Metals

3Stoichometry

3.1Formulae

3.1.1Understanding Formulae

3.1.2Empirical Formula

3.1.3Stoichiometry - Formulae, Word & Symbol Equations

3.1.4Deduce & Write Ionic Compound Formulas

3.2Relative Masses of Atoms & Molecules

3.2.1Relative Atomic Mass

3.2.2Relative Molecular Mass (Mr)

3.2.3Calculating Reacting Masses

3.3The Mole & the Avogadro Constant

3.3.1Introducing Moles

3.3.2Amounts of Substances

3.3.3Moles & Equations

3.3.4Calculations Involving Gases

3.3.5Calculating Stoichiometric Reacting Masses

3.3.6Calculating the Moles of Solute

3.3.7Calculating Empirical Formula

3.3.8Chemical Equations

3.3.9Percentage Yield

3.3.10Calculating Yield

3.3.11Percentage Purity

4Electrochemistry

4.1Electrolysis

4.1.1Electrolytic Process

4.1.2Electrolysis Examples

4.1.3Electrolysis of a Binary Compound in Molten State

4.1.4Electroplating

4.1.5Transfer of Charge During Electrolysis

4.1.6Electrolysis of Aqueous Solutions

4.1.7Electrolysis of Copper Sulfate

4.1.8Electrolysis of Halide Compounds

4.1.9Half-Equations

4.1.10Combustion of Hydrocarbons

4.2Hydrogen–Oxygen Fuel Cells

4.2.1Fuel Cells

4.2.2Hydrogen Fuel Cells

4.2.3Comparing Hydrogen-Oxygen Fuel Cells & Petrol

5Chemical Energetics

5.1Exothermic & Endothermic Reactions

5.1.1Energy Conservation

5.1.2Exothermic Reactions

5.1.3Endothermic Reactions

5.1.4Energy Change of a Reaction

5.1.5Reaction Pathway Diagrams

5.1.6Calculating Enthalpy Change

6Chemical Reactions

6.1Physical & Chemical Changes

6.1.1Difference btwn Physical & Chemical Changes

6.2Rate of Reaction

6.2.1Collision Theory & Rate of Reaction

6.2.2Factors Affecting Rate of Reaction

6.2.3Investigating Rate of Reaction by Change in Mass

6.2.4Investigating Rate - Formation of a Gas

6.2.5Evaluating Methods to Investigate Reaction Rates

6.3Reversible Reactions & Equilibrium

6.3.1Reversible Reactions

6.3.2Conditions & Equilibrium

6.3.3Dynamic Equilibrium

6.3.4Changing Conditions - Heat & Water Effects

6.3.5Factors Affecting Equilibria - Temperature

6.3.6Factors Affecting Equilibria - Pressure

6.3.7Factors Affecting Equilibria - Concentration

6.3.8The Haber Process

6.3.9The Haber Process Equation

6.4Redox

6.4.1Redox Reactions

6.4.2Redox Reactions - OIL RIG

6.4.3Examples of Redox Reactions

6.4.4Identifying Redox Reactions

6.4.5Identifying Redox Reactions by Colour Changes

6.4.6Testing for Oxidising & Reducing Agents

7Acids, Bases & Salts

7.1The Characteristic Properties of Acids & Bases

7.1.1Acids & Alkali

7.1.2Reactions of Metals with Acids

7.1.3Reactions of Bases with Acids

7.1.4Reactions of Carbonates with Acids

7.1.5Identifying Acids

7.1.6Properties & Effects of Acids

7.1.7Properties of Bases - Reactions with Acids & Salts

7.1.8Properties of Alkalis & Indicators

7.1.9Strong vs Weak Acids

7.1.10Strong vs Weak Bases

7.1.11Understanding Universal Indicator Paper

7.1.12Acids, Bases & the Neutralisation Reaction

7.2Oxides

7.2.1Oxides

7.2.2Amphoteric Oxides - Reacting with Acids & Bases

7.3Preparation of Salts

7.3.1Soluble Salts

7.3.2Preparing Soluble Salts

7.3.3Solubility of Salts

7.3.4Preparing Insoluble Salts & Crystallisation

8The Periodic Table

8.1Arrangement of Elements

8.1.1The Periodic Table

8.1.2Metals & Non-Metals

8.2Group I Properties

8.2.1Alkali Metals

8.2.2Alkali Metals - Properties

8.2.3Reactivity of Alkali Metals

8.2.4Alkali Metals & Water

8.3Group VII Properties

8.3.1The Halogens - Properties

8.3.2The Halogens - Colours & States

8.3.3The Halogen - Displacement 1

8.3.4The Halogen - Displacement 2

8.4Transition Elements

8.4.1Transition Metals

8.4.2Transition Metals - Special Properties

8.5Noble Gases

8.5.1Noble Gases - Properties

9Metals

9.1Properties of Metals

9.1.1Physical Properties of Metals

9.1.2Chemical Properties of Metals

9.1.3Metal Oxides

9.2Uses of Metals

9.2.1Uses of Metals: Aluminium & Copper

9.3Alloys & Their Properties

9.3.1Alloys

9.3.2Alloys 2

9.3.3Alloys & their Uses in Everyday Life

9.3.4Structural Diagrams of Alloys

9.3.5Structure of Alloys & Their Strength

9.4Reactivity Series

9.4.1Metals - Reactivity Series & Reactivity

9.4.2Order of Reactivity

9.4.3Reactivity of Metals

9.5Corrosion of Metals

9.5.1Corrosion

9.5.2Preventing Corrosion

9.6Extraction of Metals

9.6.1Extraction of Metals

9.6.2Extracting Iron

9.6.3Extracting Aluminium from Bauxite

10Chemistry of the Environment

10.1Water

10.1.1Testing & Treating Water

10.1.2Testing Water Purity Using Melting Point

10.1.3Water from Natural Sources

10.1.4Potable Water

10.2Fertilisers

10.2.1Nitrogen & Fertilisers

10.3Air Quality & Climate

10.3.1Gases in the Atmosphere

10.3.2Common Atmospheric Pollutants

10.3.3Consequences of Atmospheric Pollutants

10.3.4Strategies to Reduce Pollution Effects

10.3.5Photochemical Reactions

10.3.6Car Engines, Nitrogen Oxides, & Converters

11Organic Chemistry

11.1Formulae, Functional Groups & Terminology

11.1.1Formula of a Molecule

11.1.2General Formulae of Organic Compounds

11.1.3Functional Groups

11.1.4Homologous Series

11.1.5Saturated & Unsaturated Organic Compounds

11.1.6Structural Formula

11.1.7Structural Isomers

11.2Naming Organic Compounds

11.2.1Drawing Displayed Formulae

11.2.2Naming Organic Compounds - Unbranched

11.2.3Naming Unbranched Esters from Alcohols & Acids

11.2.4Naming Structural Formulae

11.3Fuels

11.3.1Fossil Fuels

11.3.2Methane as the Main Constituent of Natural Gas

11.3.3Fuels & Hydrocarbons

11.3.4Petroleum - A Mixture of Hydrocarbons

11.3.5Fractional Distillation

11.3.6Fractions

11.3.7Uses of Fractions - Fuels

11.4Alkanes

11.4.1Alkanes

11.4.2Properties of Alkanes

11.4.3Substitution Reactions of Alkanes with Chlorine

11.5Alkenes

11.5.1Alkenes

11.5.2Shortest Alkenes

11.5.3Reactions of Alkenes

11.5.4Types of Alkene Reactions

11.5.5Cracking

11.5.6Testing Saturated & Unsaturated Hydrocarbons

11.5.7Properties of Alkenes - Addition Reactions

11.6Alcohols

11.6.1Alcohols

11.6.2Smallest Alcohols

11.6.3Fermentation

11.6.4Steam

11.6.5Fermentation vs Hydration of Ethene

11.6.6Manufacture of Ethanol: Fermentation & Hydration

11.6.7Combustion of Ethanol

11.6.8Uses of Ethanol - Solvent & Fuel

11.6.9Advantages & Disadvantages of Ethanol Manufacture

11.7Carboxylic Acids

11.7.1Carboxylic Acids

11.7.2Smallest Carboxylic Acids

11.7.3Reactions of Carboxylic Acids

11.7.4Formation of Ethanoic Acid

11.8Polymers

11.8.1Polymers

11.8.2Problems With Polymers

11.8.3Polymers & Plastics

11.8.4Problems with Plastics

11.8.5Condensation Polymerisation

11.8.6Condensation Polymerisation Examples

11.8.7Addition Polymerisation

11.8.8Addition Polymerisation Examples

11.8.9Structure of Polymers

11.8.10Natural Polyamides - Proteins & Amino Acids

12Experimental Techniques & Chemical Analysis

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