Grade 10
  1. Matter and its properties  1.1. States of matter  1.2. Physical and chemical properties of matter  1.3. Classification of substances (elements, compounds, mixtures)  1.4. Changes in Matter (Physical and Chemical Changes)  1.5. Law of conservation of mass and law of definite proportions
  2. Atomic Structure  2.1. Historical development of the atomic model  2.2. Subatomic particles (protons, neutrons, electrons)  2.3. Atomic number, mass number and isotopes  2.4. Electronic Configuration and Energy Levels  2.5. Valency, ion formation and oxidation state
  3. Periodic table  3.1. History and Development of the Periodic Table  3.2. Modern Periodic Law and Periodic Trends  3.3. Groups and Periods in the Periodic Table  3.4. Trends in the Periodic Table  3.5. Metals, non-metals, metalloids and their properties  3.6. Noble gases and their chemical inertness
  4. Chemical bond  4.1. Formation of Chemical Bonds (Octet Rule)  4.2. Ionic Bonding and Properties of Ionic Compounds  4.3. Covalent Bond and Properties of Covalent Compounds  4.4. Metallic bond and its properties  4.5. Molecular geometry and VSEPR theory  4.6. Polarity and dipole moment of molecules  4.7. Intermolecular forces
  5. Chemical Reactions and Equations  5.1. Types of Chemical Reactions  5.2. Writing and balancing chemical equations  5.3. Law of conservation of mass in chemical reactions  5.4. Factors Affecting Chemical Reactions  5.5. Catalysts and their role in chemical reactions  5.6. Exothermic and Endothermic Reactions
  6. Stoichiometry and Chemical Calculations  6.1. Mole concept and Avogadro number  6.2. Molar Mass and Gram-Mole Conversions  6.3. Empirical and molecular formula  6.4. Stoichiometric calculations and chemical yield  6.5. Limiting and Excess Reactants
  7. Acids, Bases and Salts  7.1. Properties and Definitions of Acids and Bases (Arrhenius, Bronsted-Lowry, Lewis)  7.2. pH Scale, pOH, and Indicators  7.3. Neutralization reactions and salt formation  7.4. Strength of Acids and Bases (Strong vs. Weak Acids and Bases)  7.5. Common Acids and Bases in Daily Life  7.6. Salts, their solubility and applications
  8. Metals and Nonmetals  8.1. Physical and chemical properties of metals  8.2. Physical and Chemical Properties of Non-Metals  8.3. Reactivity Series of Metals and Displacement Reactions  8.4. Extraction of metals from ores  8.5. Corrosion, its causes and prevention  8.6. Alloys, their composition and uses
  9. Carbon and its compounds  9.1. Allotropes of Carbon  9.2. Hydrocarbons and their classification (alkanes, alkenes, alkynes)  9.3. Functional groups in organic compounds  9.4. Nomenclature of organic compounds (IUPAC system)  9.5. Isomerism in organic chemistry (structural and geometrical)  9.6. Important organic reactions (combustion, addition, substitution, polymerization)  9.7. Applications of organic compounds in industry and daily life
  10. Environmental Chemistry  10.1. Air Pollution (Sources, Effects and Control)  10.2. Water Pollution (Causes, Effects and Remedies)  10.3. Greenhouse effect and global warming  10.4. Ozone layer depletion and its effects  10.5. Green Chemistry and Its Applications  10.6. sustainable chemistry practice
  11. Thermochemistry  11.1. Heat and Energy Changes in Chemical Reactions  11.2. Exothermic and Endothermic Reactions  11.3. Enthalpy, enthalpy change, and heat of reaction  11.4. Specific heat capacity and calorimetry  11.5. Energy Changes in Combustion Reactions
  12. Electrochemistry  12.1. Electrolytes and non-electrolytes  12.2. Electrolysis and its applications (electroplating, extraction of metals)  12.3. Redox reactions (oxidation and reduction)  12.4. Galvanic cell and electrochemical series  12.5. Corrosion and electrochemical prevention methods
  13. Chemical kinetics and equilibrium  13.1. Rate of chemical reactions and its measurement  13.2. Factors affecting the reaction rate (catalyst, temperature, concentration)  13.3. Reversible and irreversible reactions  13.4. Dynamic equilibrium and equilibrium constant  13.5. Le Chatelier's principle and its applications
  14. Gases and Gas Laws  14.1. Properties of gases and kinetic molecular theory  14.2. Boyle's Law (Pressure-Volume Relation)  14.3. Charles's Law  14.4. Gay-Lussac's Law  14.5. Combined Gas Law and Ideal Gas Law  14.6. Real Gases vs Ideal Gases
  15. Nuclear Chemistry  15.1. Introduction to Radioactivity and Nuclear Reactions  15.2. Types of radioactive decay (alpha, beta, gamma)  15.3. Half-life and applications of radioactive isotopes  15.4. Nuclear fission and fusion reactions  15.5. Nuclear power generation and its environmental impact

Grade 10 → Chemical Reactions and Equations ↓


Exothermic and Endothermic Reactions


Chemical reactions are processes where one or more substances change into one or more different substances. They involve the breaking and formation of bonds between atoms. During these reactions, there is often a change in energy as well. This energy change can result in the absorption or emission of energy. In chemistry, these types of reactions are classified as exothermic or endothermic depending on where the energy goes.

Understanding chemical reactions

In any chemical reaction, bonds in the reactants are broken, and new bonds are formed to form products. Breaking bonds requires energy, while forming bonds releases energy. The difference in energy between these two processes results in a change in the overall energy of the reaction.

Exothermic reactions

Exothermic reactions release energy into the surroundings, usually in the form of heat. This happens when the energy needed to break the bonds in the reactants is less than the energy released when new bonds are formed in the products. As a result, the temperature of the surroundings rises.

A classic example of an exothermic reaction is the combustion of methane gas:

CH 4 + 2O 2 → CO 2 + 2H 2 O + energy

In this reaction, methane (CH 4) burns in the presence of oxygen (O 2), resulting in the formation of carbon dioxide (CO 2) and water (H 2 O) with the release of energy.

Another example of an exothermic reaction is the reaction between hydrochloric acid and sodium hydroxide:

HCl + NaOH → NaCl + H 2 O + energy

Here, hydrochloric acid reacts with sodium hydroxide to form sodium chloride and water, releasing energy.

Visual example of an exothermic reaction

Reactants Products Energy release

The diagram above shows an exothermic reaction. Note that the energy level of the products is lower than that of the reactants, indicating the release of energy into the surrounding environment.

Endothermic reactions

Endothermic reactions absorb energy from the surroundings. This happens when more energy is needed to break bonds in the reactants than is released when new bonds are formed in the products. As a result, the temperature of the surroundings decreases.

A well-known example of an endothermic reaction is the thermal decomposition of calcium carbonate:

CaCO 3 + energy → CaO + CO 2

In this reaction, calcium carbonate (CaCO 3) decomposes to form calcium oxide (CaO) and carbon dioxide (CO 2), absorbing energy when heated.

Photosynthesis is another example of an endothermic reaction:

6CO 2 + 6H 2 O + energy → C 6 H 12 O 6 + 6O 2

In this process, plants take in carbon dioxide and water, and produce glucose and oxygen using the sun's energy.

Visual example of an endothermic reaction

Reactants Products Energy Absorption

The diagram above shows an endothermic reaction. Note that the energy level of the products is higher than that of the reactants, indicating energy absorption from the surroundings.

Comparison of exothermic and endothermic reactions

Criteria Exothermic reactions Endothermic reactions
Energy transformation Energy is released. Energy is absorbed.
Temperature Change The surrounding temperature increases. The surrounding temperature decreases.
Example Combustion, neutralization Photosynthesis, thermal decomposition

Factors affecting exothermic and endothermic reactions

Several factors affect the energy changes in exothermic and endothermic reactions:

Nature of reactants and products

The type of bonds that are broken and formed plays an important role. Stronger bonds require more energy to break and release more energy when formed. For example, in combustion reactions, the strong carbon-hydrogen bonds in hydrocarbons release a lot of energy when they react with oxygen.

Concentration of reactants

Concentration affects the rate and extent of the reaction. In an exothermic reaction, higher concentrations of reactants usually lead to more energy being released because more molecules are available to react. In endothermic reactions, higher concentrations of reactants can increase the energy absorbed, because more energy is needed to enable the reaction to occur.

Pressure and volume

Changes in pressure and volume can affect reactions, especially those involving gases. Increasing pressure by reducing volume often increases the reaction rate and the energy change in reactions can be altered by affecting the frequency of collisions of molecules.

Temperature

Temperature affects reaction rates and energy changes. In exothermic reactions, increasing the temperature can reduce the amount of net energy released to the surroundings, because some of this energy is used to further increase the temperature. For endothermic reactions, raising the temperature provides the energy needed to break bonds, allowing the reaction to proceed.

Applications and implications

Everyday examples

Exothermic and endothermic reactions are found in everyday life. Heat packs used for warmth involve exothermic reactions, while cooking and baking food, which absorb heat, are examples of endothermic processes.

Industrial applications

In industries, exothermic reactions are used for heating purposes, such as in power plants and manufacturing processes. Endothermic reactions are important in processes such as photosynthesis, which is vital to oxygen production and life on Earth.

Environmental impact

If exothermic reactions are not properly controlled, industrial use can contribute to global warming due to the release of heat and greenhouse gases. Understanding and optimizing these reactions is essential to minimize their environmental impact.


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Exothermic and Endothermic Reactions

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