3.1.5

Equations & Formula

Test yourself

Balancing Chemical Equations

Chemical equations must be balanced to make sure that there are the same number of atoms of each element before and after a reaction. The reaction of hydrogen with oxygen to make water will be used as an example of how to do this:

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Unbalanced equation

  • The unbalanced symbol equation for this reaction is:
    • H2 + O2 → H2O
  • The equation is unbalanced because there are 2 atoms of oxygen on the left hand side of the equation, but only 1 on the right hand side.
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Still unbalanced equation

  • We can increase the number of oxygen atoms on the right hand side by adding an H2O molecule:
    • H2 + O2 → 2H2O
  • However, the equation is still unbalanced as there are now more hydrogen atoms on the right hand side than on the left hand side.
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Balanced equation

  • The final step is to add an H2 molecule to the left hand side:
    • 2H2 + O2 → 2H2O
  • Our equation is now balanced.

Molecular vs Empirical Formula

The molecular formula shows the actual amount of atoms which make up a molecule. The empirical formula shows the simplest ratio of atoms which make up a molecule.

Illustrative background for Molecular formulaIllustrative background for Molecular formula ?? "content

Molecular formula

  • The molecular formula shows the actual amount of atoms which make up a molecule.
    • E.g. glucose = C6H12O6
Illustrative background for Empirical formulaIllustrative background for Empirical formula ?? "content

Empirical formula

  • The empirical formula shows the simplest ratio of atoms which make up a molecule.
    • E.g. glucose = CH2O

Jump to other topics

1Atomic Structure

1.1Atoms & Elements

1.1.1Elements & Compounds

1.1.2Chemical Reactions & Equations

1.1.3Mixtures

1.1.4Separating Mixtures

1.1.5Model of the Atom

1.1.6Atom Size & Number

1.1.7Atomic Number - Calculations

1.1.8Isotopes

1.1.9Isotopes HyperLearning

1.1.10Isotopes - Calculations

1.1.11Relative Atomic Mass

1.1.12Electron Structure

1.1.13Periodic Table

1.1.14Metals & Non-Metals

1.1.15Noble Gases

1.1.16Halogens

1.1.17Alkali Metals

1.1.18Transition Metals

1.1.19End of Topic Test - Atomic Structure

1.1.20Grade 9 - Atoms & Elements

1.1.21Exam-Style Questions - Atomic Structure

1.1.22Application Questions - Atomic Structure

2Chemical Bonding

2.1Chemical Bonds

2.1.1Types of Bonds

2.1.2Ionic Bonds

2.1.3Ionic Compounds

2.1.4Covalent & Metallic Bonds

2.1.5Representing Covalent Bonds

2.1.6Dots-And-Cross Diagrams

2.1.7Exam-Style Questions - Chemical Bonds

2.2States of Matter

2.2.1States of Matter

2.2.2Changing State

2.2.3Changing State HyperLearning

2.2.4State Symbols

2.2.5Exam-Style Questions - States of Matter

2.3Chemical Properties

2.3.1Chemical Properties of Ionic Compounds

2.3.2Chemical Properties of Small Molecules

2.3.3Molecular Forces & Polymers

2.3.4Metals & Giant Covalent Structures

2.3.5Alloys & Conductors

2.3.6Carbon Structures - Diamond & Graphite

2.3.7Carbon Structures - Graphene & Fullerenes

2.3.8Carbon Structures - Summary

2.3.9Nanoparticles

2.3.10Nanotechnology

2.3.11Surface Area to Volume Ratio & Nanotechnology Uses

2.3.12End of Topic Test - Chemical Bonding

2.3.13Grade 9 - Bonding & Structure

2.3.14Exam-Style Questions - Allotropes of Carbon

3Quantitative Chemistry

3.1Chemical Measurements

3.1.1Conservation of Mass

3.1.2Relative Formula Mass

3.1.3Relative Formula Mass - Calculations

3.1.4Measuring Mass

3.1.5Equations & Formula

3.1.6Moles 1

3.1.7Moles 2

3.1.8Moles 3

3.1.9Moles - Calculations

3.1.10Percentage Yield

3.1.11Percentage Yield - Calculations

3.1.12Moles & Yield

3.1.13Atom Economy

3.1.14Atom Economy - Calculations

3.1.15Concentrations & Amounts

3.1.16Amount of Substance in Relation to Volumes and Gas

3.1.17Concentrations & Amounts - Calculations

3.1.18Empirical Formula - Calculations

3.1.19End of Topic Test - Quant Chemistry

3.1.20Grade 9 - Quantitative Chemistry

3.1.21Exam-Style Questions - Moles

4Chemical Changes

4.1Acids, Alkalis & Redox Reactions

4.1.1Acids & Alkalis

4.1.2Redox Reactions

4.2Reactivity of Metals

4.2.1Reactivity Diagram

4.2.2Displacement Reactions

4.2.3Reactions with Water & Acid

4.2.4Reactivity Tests

4.2.5Extraction of Metals

4.2.6Exam-Style Questions - Displacement Reactions

4.3Reactions of Acids

4.3.1Reactions of Metals with Acids

4.3.2Neutralisation of Acids

4.3.3Soluble Salts

4.3.4Required Practical: Separating Mixtures

4.3.5The pH Scale

4.3.6Measuring pH

4.3.7Neutralisation & Titrations 1

4.3.8Neutralisation & Titrations 2

4.3.9Strong and Weak Acids

4.4Electrolysis

4.4.1Electrolysis

4.4.2Metal Extraction

4.4.3Electrolysis of Aqueous Solutions & Half Equations

4.4.4End of Topic Test - Chemical Changes

4.4.5Grade 9 - Chemical Changes

4.4.6Exam-Style Questions - Electrolysis

5Energy Changes

5.1Exothermic & Endothermic Reactions

5.1.1Energy Conservation

5.1.2Exothermic & Endothermic Reactions

5.1.3Reaction Profiles

5.1.4Reaction Profiles 2

5.2Chemical Cells & Fuel Cells

5.2.1Chemical Cells

5.2.2Batteries & Charging of Cells

5.2.3Fuel Cells

5.2.4Hydrogen Fuel Cell

5.2.5End of Topic Test - Energy Changes

5.2.6Grade 9 - Energy Changes

5.2.7Exam-Style Questions - Fuel Cells

6The Rate & Extent of Chemical Change

6.1Rate of Reaction

6.1.1Chemical Reactions

6.1.2Collision Theory

6.1.3Catalysts

6.1.4Catalysts in Industry

6.2Reversible Reactions

6.2.1Reversible Reactions

6.2.2Equilibrium

6.2.3Equilibrium Position

6.2.4Equilibrium Position 2

6.2.5End of Topic Test - Rates of Reaction

6.2.6Grade 9 - Rate & Extent of Chemical Change

6.2.7Exam-Style Questions - Reversible Reactions

7Organic Chemistry

7.1Carbon Compounds

7.1.1Crude Oil

7.1.2Alkanes

7.1.3Fractional Distillation

7.1.4Homologous Series

7.1.5Burning Hydrocarbons

7.1.6Cracking

7.1.7Uses of Alkenes

7.1.8Exam-Style Questions - Organic Compounds

7.2Alkenes & Alcohols

7.2.1Structure of Alkenes

7.2.2Reactions of Alkenes

7.2.3End of Topic Test - Alkanes & Alkenes

7.2.4Alcohols

7.2.5Reactions of Alcohols

7.2.6Carboxylic Acids

7.2.7Reactions of Carboxylic Acids

7.2.8Addition Polymers

7.2.9Condensation Polymers

7.2.10Naturally Occurring Polymers - Proteins

7.2.11Naturally Occurring Polymers - DNA & Sugars

7.2.12End of Topic Test - Alcohols, Acids & Polymers

7.2.13Grade 9 - Organic Chemistry

7.2.14Exam-Style Questions - Alcohols

8Chemical Analysis

8.1Purity, Formulations & Chromatography

8.1.1Purity & Formulations

8.1.2Chromatography

8.1.3Paper Chromatography 1

8.1.4Paper Chromatography 2

8.1.5Required Practical - Paper Chromatography

8.2Identification of Common Gases

8.2.1Identification of Hydrogen & Oxygen

8.2.2Identification of Carbon Dioxide & Chlorine

8.3Identifying Ions

8.3.1Flame Tests

8.3.2Required Practical: Flame Tests

8.3.3Metal Hydroxides

8.3.4Carbonates

8.3.5Halides, Sulfates

8.3.6Methodology for Chemical Analysis

8.3.7Flame Emission Spectroscopy

8.3.8End of Topic Test - Chemical Analysis

8.3.9Grade 9 - Chemical Analysis

8.3.10Exam-Style Questions - Identification of ions

9Chemistry of the Atmosphere

9.1The Earth's Atmosphere

9.1.1Proportions of Gases in the Atmosphere

9.1.2Oxygen & Carbon Dioxide in the Atmosphere

9.1.3Greenhouse Gases & Human Activities

9.1.4Greenhouse Gases & Human Activities

9.1.5Greenhouse Gases & Climate Change

9.1.6Carbon Footprints

9.1.7Common Atmospheric Pollutants & Their Properties

9.1.8End of Topic Test - The Earth

9.1.9Grade 9 - Chemistry of the Atmosphere

9.1.10Exam-Style Questions - Earth's Atmosphere

10Using Resources

10.1Using the Earth's Resources

10.1.1Potable Water & its Sources

10.1.2Potable Water in the UK & in Saudi Arabia

10.1.3Natural Resources

10.1.4Waste Water

10.1.5Metal Ore Extraction & the Properties of Copper

10.1.6Overexploitation & Alternative Extraction Methods

10.2Life Cycle Assessments & Recycling

10.2.1Life Cycle Assessments

10.2.2Difficulties with LCA

10.2.3Reducing Resource Usage

10.2.4Reducing Use of Metal and Glass

10.2.5Exam-Style Questions - Life Cycle Assessments

10.3Using Materials

10.3.1Corrosion

10.3.2Alloys

10.3.3Ceramics

10.3.4Polymers & Composites

10.4The Haber Process & NPK Fertilisers

10.4.1The Haber Process

10.4.2The Haber Process - Equation & Trade-Offs

10.4.3Formulated vs Manure Fertilisers

10.4.4NPK Fertilisers 1

10.4.5NPK Fertilisers 2

10.4.6End of Topic Test - Resources

10.4.7Grade 9 - Using Resources

10.4.8Exam-Style Questions - The Haber Process

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Measuring Mass

Moles 1