Grade 8
  1. Introduction to Chemistry  1.1. Nature and scope of chemistry  1.2. Importance of chemistry in daily life  1.3. Chemistry and its relation with other sciences  1.4. The role of chemistry in industry, medicine and the environment  1.5. Scientific investigation and experimental methods in chemistry
  2. Matter and its properties  2.1. Definition and classification of matter  2.2. Physical and chemical properties of matter  2.3. Law of conservation of matter  2.4. Extensive and Intensive Properties of Matter  2.5. Kinetic molecular theory of matter  2.6. States of matter: solids, liquids, gases, plasmas, and Bose-Einstein condensates  2.7. Changes in state and energy are involved  2.8. Diffusion and Brownian motion
  3. Elements, Compounds, and Mixtures  3.1. Definition and differences between elements, compounds, and mixtures  3.2. Atomic Structure and Atomic Number  3.3. Chemical symbols and formulas  3.4. Trends in the Periodic Table (Groups and Periods)  3.5. Classification of Elements: Metals, Nonmetals and Metalloids  3.6. Rare Earth Elements and Transition Metals  3.7. Types of mixtures: homogeneous and heterogeneous  3.8. Separation of Mixtures Using Physical and Chemical Methods
  4. Separation Techniques  4.1. Filtration, Sedimentation and Decantation  4.2. Evaporation and crystallization  4.3. Distillation and Fractional Distillation  4.4. Chromatography and its applications  4.5. Sublimation in the purification of compounds  4.6. The role of centrifugation in biochemical processes
  5. Atomic Structure  5.1. Dalton's atomic theory  5.2. Structure of the atom: protons, neutrons and electrons  5.3. Bohr's atomic model  5.4. Introduction to Quantum Mechanical Model  5.5. Electron Configuration and Energy Levels  5.6. Excitation and emission spectra  5.7. Isotopes and their applications
  6. Periodic Table and Chemical Trends  6.1. History and Development of the Periodic Table  6.2. Modern periodic law  6.3. Periodicity and trends in atomic and ionic sizes  6.4. Ionization Energy, Electron Affinity and Electronegativity  6.5. Introduction to Lanthanides and Actinides  6.6. Application of periodic trends in chemistry
  7. Chemical Bonding and Molecular Structure  7.1. Types of chemical bonds: ionic, covalent and metallic bonds  7.3. Polar and Nonpolar Molecules  7.4. Hydrogen bonding and its applications  7.5. Intermolecular forces: dipole-dipole, London dispersion force
  8. Chemical Reactions and Stoichiometry  8.1. Chemical Equations and Balance  8.2. Types of Chemical Reactions: Combination, Decomposition, Displacement and Redox  8.3. Introduction to stoichiometry and the mole concept  8.4. Limiting reactant in chemical equations  8.5. Reaction rate, catalyst, and factors affecting reaction rate
  9. Acids, Bases and Salts  9.1. Definition and Properties of Acids and Bases  9.2. Strong vs. Weak Acids and Bases  9.3. pH Scale and pH Calculation  9.4. Neutralization reactions  9.5. Buffer solutions and their importance  9.6. Applications of Acids, Bases and Salts in Daily Life
  10. Solutions and Solubility  10.1. Definition of Solution, Solute, and Solvent  10.2. Factors Affecting Solubility  10.3. Concentration units: molarity and molality  10.4. Saturated, unsaturated and supersaturated solutions  10.5. Concept of osmosis and reverse osmosis  10.6. Concentrative properties of solutions
  11. Gases and Gas Laws  11.1. Properties of gases  11.2. Introduction to Ideal and Real Gases  11.3. Boyle's Law, Charles' Law and Avogadro's Law  11.4. Ideal Gas Equation and Its Applications  11.5. Application of Gas Laws in Real Life
  12. Thermochemistry and energy transformation  12.1. Energy in Chemical Reactions  12.2. Exothermic vs. Endothermic Reactions  12.3. Heat and Enthalpy Changes  12.4. Calorimetry and heat transfer in reactions
  13. Metals and Nonmetals  13.1. Physical and Chemical Properties of Metals and Nonmetals  13.2. Reactivity Series of Metals  13.3. Corrosion and its prevention  13.4. Extraction of metals from ores  13.5. Uses of metals and non-metals in daily life
  14. Introduction to Organic Chemistry  14.1. Characteristics of carbon and organic compounds  14.2. Functional groups and their importance  14.3. Simple Hydrocarbons: Alkenes, Alkenes and Alkynes  14.4. Isomerism in organic compounds  14.5. Introduction to polymers and their uses
  15. Environmental Chemistry and Sustainability  15.1. Green Chemistry Principles  15.2. Effects of Chemical Pollution on Ecosystems  15.3. Acid rain and its effects  15.4. Ozone layer depletion and global warming  15.5. Waste Management and Recycling in Chemistry

Grade 8 → Thermochemistry and energy transformation ↓


Exothermic vs. Endothermic Reactions


In chemistry, it is important to understand how energy is absorbed or released during a chemical reaction. This is where the concepts of exothermic and endothermic reactions come into play. These reactions are identified based on whether they release or absorb energy, usually in the form of heat.

Introduction to thermochemistry

Thermochemistry is the study of the energy changes that occur during chemical reactions and changes in state. When substances react, they either absorb or release energy, causing temperature changes or even phase transitions. This energy is measured primarily in terms of heat transfer.

What is an exothermic reaction?

An exothermic reaction is a chemical reaction in which energy is released by light or heat. In this process, the total energy of the products is less than the energy of the reactants. The difference in energy is released as heat.

Example of exothermic reaction:

Combustion of methane: CH4 + 2O2 → CO2 + 2H2O + Energy

Here, when methane (CH 4) burns, it reacts with oxygen (O 2) to form carbon dioxide (CO 2) and water (H 2 O), releasing energy in the process.

Visual example:

Reactants Products Energy free

What is an endothermic reaction?

In contrast, an endothermic reaction is one that absorbs energy from its surroundings. This energy is usually taken up as heat, meaning the surroundings cool down as the reaction occurs. In endothermic reactions, the products have more energy than the reactants.

Example of endothermic reaction:

Photosynthesis: 6CO2 + 6H2O + Energy → C6H12O6 + 6O2

During photosynthesis, plants convert carbon dioxide and water into glucose and oxygen by absorbing energy from sunlight. This is an energy-consuming process.

Visual example:

Reactants Products Absorbed Energy

Understanding energy diagrams

Energy diagrams help show how energy changes during a chemical reaction. In an exothermic reaction, the energy level of the reactants is higher than the energy level of the products. As the reaction proceeds, energy is released, often as heat, and the temperature of the system increases.

On the other hand, in an endothermic reaction, the energy level of the products is higher than that of the reactants. Energy is absorbed from the surrounding, resulting in a decrease in temperature.

Factors affecting reaction energy

Several factors can affect the amount of energy absorbed or emitted during a chemical reaction, including:

  • Nature of reactants: Different substances require different amounts of energy to react.
  • Concentration: High concentrations can affect how much energy is released or absorbed.
  • Temperature: Increasing the temperature can provide additional energy to the reactants, affecting the energy change.
  • Presence of catalysts: Catalysts can lower the activation energy required for a reaction to occur, thereby changing the energy dynamics.

Role of activation energy

Activation energy is the minimum energy required for a reaction to occur. Even in exothermic reactions, an initial input of energy is required to break bonds in the reactants before new bonds can form in the products. This activation energy is often represented as a peak in energy diagrams.

Activation energy in exothermic reactions

In exothermic reactions, once the activation energy is provided, energy is released as new bonds are formed, and the products reach a lower energy level than the reactants.

Activation energy in endothermic reactions

Endothermic reactions require a constant supply of energy not only to overcome the activation energy but also to ensure that the reaction can proceed to form products with a higher energy level.

Everyday examples of exothermic and endothermic reactions

Understanding these reactions is not just an academic exercise; they also have practical applications in daily life.

Exothermic reactions in daily life

  • Lighting a match: As a match burns, it releases energy in the form of heat and light.
  • Burning wood: Combustion reactions are always exothermic, releasing energy to heat your home.
  • Respiration: When we metabolize food, energy is released for the body to use.

Endothermic reactions in daily life

  • Photosynthesis: Plants absorb sunlight to make food.
  • Cooking: Boiling an egg or baking a cake absorbs heat, which causes a chemical change in the food.
  • Instant cold packs: Often used in sports injuries, these packs rely on endothermic reactions to absorb heat and provide cooling.

Conclusion

Understanding exothermic and endothermic reactions is fundamental in chemistry. These concepts explain how energy is transferred and transformed, which affects both laboratory reactions and everyday phenomena. Shedding light on the balance of energy in reactions not only makes chemistry fascinating, but also enables us to use this energy in a variety of applications, from industrial processes to personal conveniences.


Grade 8 → 12.2


U
username
0%
completed in Grade 8

← Prev (12.1)
Energy in Chemical Reactions
Next (12.3) →
Heat and Enthalpy Changes

Comments 



Exothermic vs. Endothermic Reactions

https://www.chemistryelite.com/g8/12.2?ceal=en