This chapter explores the concepts of atoms and molecules, including their definitions, properties, and significance in understanding matter.
ATOMS AND MOLECULES – Formula & Equation Sheet
Essential formulas and equations from Science, tailored for Class 9 in Science.
This one-pager compiles key formulas and equations from the ATOMS AND MOLECULES chapter of Science. Ideal for exam prep, quick reference, and solving time-bound numerical problems accurately.
Key concepts & formulas
Essential formulas, key terms, and important concepts for quick reference and revision.
Formulas
Law of Conservation of Mass: m_{reactants} = m_{products}
The total mass of the reactants equals the total mass of the products in a chemical reaction. This law asserts mass is neither created nor destroyed during chemical changes.
Law of Definite Proportions: rac{m_1}{m_2} = rac{n_1 \cdot M_1}{n_2 \cdot M_2}
In a compound, the elements are always present in fixed proportions by mass. This can be expressed by comparing the mass ratios of the elements and their respective molar masses.
Atomic Mass Unit (u): u = rac{1}{12} m_{C-12}
The atomic mass unit is defined as one-twelfth of the mass of a carbon-12 atom. It is used as a standard for expressing atomic masses of other elements.
Molecular Mass: M = \sum (n_i \cdot m_i)
The molecular mass of a molecule is the sum of the atomic masses of all atoms in the molecule, where n is the number of each type of atom, and m is the atomic mass.
Chemical Formula: ext{Compound} = ext{Element}_{n_1}^{ ext{Valency}_1} ext{Element}_{n_2}^{ ext{Valency}_2}
The chemical formula represents the composition of a compound, with subscripts indicating the number of atoms and superscripts their valency.
Empirical Formula: (CH_2O)
The empirical formula gives the simplest whole-number ratio of atoms in a compound, e.g., the empirical formula for glucose is CH₂O.
Ion Formation: ext{Cation} (Na^+) + ext{Anion} (Cl^-) = NaCl
A cation combines with an anion to form a neutral ionic compound. Cations are positively charged, and anions are negatively charged.
Valency: ext{Valency} = ext{Number of Bonds Formed}
Valency indicates an element's ability to combine with others, often equal to the number of electrons it can lose, gain, or share.
Molecular Formula: ext{C}_6 ext{H}_{12} ext{O}_6
The molecular formula specifies the actual number of each type of atom in a molecule of the compound, e.g., glucose has 6 carbon, 12 hydrogen, and 6 oxygen atoms.
Combustion Reaction: C_xH_y + O_2 → CO_2 + H_2O
In a combustion reaction, a hydrocarbon reacts with oxygen to produce carbon dioxide and water. The coefficients in front of each component are determined based on balancing the reaction.
Equations
Na2CO3 + 2 CH3COOH → 2 C2H3O2Na + CO2 + H2O
This reaction illustrates the neutralization of sodium carbonate by acetic acid, producing sodium acetate, carbon dioxide, and water.
H2 + ½ O2 → H2O
This represents the formation of water from hydrogen and oxygen, showcasing the law of definite proportions in the relationship between the elements.
C + O2 → CO2
This combustion reaction produces carbon dioxide from carbon and oxygen, demonstrating the element composition's fixed ratio.
NH3 + HCl → NH4Cl
This is the reaction between ammonia and hydrochloric acid, forming ammonium chloride, which exemplifies the principles of neutralization reactions.
Mg + 2 HCl → MgCl2 + H2
Magnesium reacts with hydrochloric acid to form magnesium chloride and hydrogen gas, illustrating a typical metal-acid reaction.
Ca(OH)2 + CO2 → CaCO3 + H2O
Calcium hydroxide reacts with carbon dioxide to form calcium carbonate and water, demonstrating the formation of a precipitate.
2 Na + 2 H2O → 2 NaOH + H2
This reaction shows sodium's reaction with water, resulting in sodium hydroxide and hydrogen gas, indicative of a vigorous chemical reaction.
AgNO3 + NaCl → AgCl + NaNO3
This double displacement reaction produces silver chloride and sodium nitrate, a classic example of ionic compound formation.
Fe2O3 + 6 HCl → 2 FeCl3 + 3 H2O
Iron (III) oxide reacts with hydrochloric acid to yield iron (III) chloride and water, illustrating both the conservation of mass and the law of definite proportions.
C6H12O6 + 6 O2 → 6 CO2 + 6 H2O
This equation represents the complete aerobic respiration of glucose, showing the conversion of glucose and oxygen into carbon dioxide and water.
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