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 → Matter and its properties ↓


Law of conservation of mass and law of definite proportions


Chemistry is a fascinating subject that explores the properties, structure, and transformation of matter. At its core, chemistry relies on several fundamental laws to understand how substances interact with one another. Two of these important laws are the law of conservation of mass and the law of definite proportions. These principles form the basis of many chemical reactions and theories. This detailed text aims to provide a comprehensive understanding of these laws with practical examples and illustrations.

Law of conservation of mass

The law of conservation of mass states that in a closed system, the mass of the reactants is equal to the mass of the products. This concept was first formulated by Antoine Lavoisier in the late 18th century. It basically means that mass is neither created nor destroyed in a chemical reaction.

Understanding the law

Imagine you have a sealed container. No matter what chemical reactions are going on inside, as long as nothing enters or leaves the container, the total mass remains unchanged. This allows chemists to predict the outcome of reactions in terms of mass. The equation is simple:

Total mass of reactants = Total mass of products

Illustrative examples

Consider the simple reaction of hydrogen gas reacting with oxygen gas to form water:

2H 2 + O 2 → 2H 2 O

Imagine a balance scale, imagine that on the left is hydrogen and oxygen gas, and on the right is the produced water. The scales should remain balanced before and after the reaction, which means that mass is conserved.

H 2 + O 2 H2O

The diagram above shows equal mass on both sides of the scale. This shows that no mass is lost or gained during the reaction.

Daily life applications

This principle is observed when baking cakes. Although the ingredients undergo a complex transformation, the total weight of the starting material remains the same as that of the final baked cake, provided there is no volume loss.

Mathematical example

Consider the reaction of zinc with hydrochloric acid to form zinc chloride and hydrogen gas:

Zn + 2HCl → ZnCl 2 + H 2

Suppose that 65 g of zinc reacts with 73 g of hydrochloric acid, forming 136 g of zinc chloride and 2 g of hydrogen gas. To verify this:

Total mass of reactants: 65 g + 73 g = 138 g.

Total mass of products: 136 g + 2 g = 138 g.

This calculation shows that mass is conserved.

Law of definite proportions

The law of definite proportions, also called the law of constant composition, states that a chemical compound will always have the same proportion of elements by mass. This concept is important to understand that a compound is made up of elements in a fixed proportion, regardless of its source or quantity.

Understanding the law

French chemist Joseph Proust proposed this law in 1794. According to Proust, river water is chemically identical to laboratory water, with a mass ratio of hydrogen and oxygen of 1:8.

Water (H 2 O): Ratio of H to O = 2:16 = 1:8 (by mass)

Illustrative examples

Consider sodium chloride (table salt), which is composed of sodium (Na) and chlorine (Cl):

NaCl

The mass ratio of sodium to chlorine in sodium chloride is consistent with:

Na : Cl = 23 : 35.5

Imagining a pie chart, each quarter of the chart could represent a specific mass portion of the compound, emphasizing that sodium and chlorine are constantly present in each portion, maintaining a fixed ratio.

No Chlorine

This diagram shows the specific elemental parts within the sodium chloride compound.

Textual examples

Let's consider carbon dioxide (CO2). No matter where you get CO2 from, whether from burning coal or from a fire, the mass ratio of carbon and oxygen in it is equal to 12:32. This consistent ratio validates the law of definite proportions.

Conceptual application

This principle is important in pharmaceuticals, where maintaining consistency in the proportions of active ingredients in a drug is essential to ensure therapeutic effectiveness. In quality control, manufacturers must guarantee to maintain a stable ingredient composition of products such as beverages worldwide.

Interrelationships between laws

The law of conservation of mass and the law of definite proportions are very closely interconnected. Both laws are the basis of modern stoichiometry used in chemical equations and reactions. They give chemists information about the expected mass output and the required input composition for accurate, predictable reactions.

When combined, these rules enable chemists to understand the balance and proportions of elements in new compounds. For example, by knowing the masses of the reactants, scientists can predict the amount of products that will form by applying these two principles together.

Conclusion

The laws of conservation of mass and definite proportions are fundamental principles in chemistry. They help chemists understand the unchanging nature of mass during chemical reactions and the fixed proportions of elements in compounds. By integrating visual and textual examples, these laws become easier to understand, providing a solid foundation for further exploration in chemistry.


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