Chemistry Mid-Term Paper 2025 Class 11 | Download Question Paper PDF

Chemistry Mid-Term Paper 2025 Class 11

Chemistry Mid-Term Paper 2025 Class 11 PDF

Chemistry Mid-Term Paper 2025 Class 11

1. Importance of Chemistry

• Chemistry is the branch of science that studies the composition, structure, properties, and transformation of matter.
• It helps in understanding:
  • Composition of substances and their changes during chemical reactions.
  • The role of chemicals in daily life — medicines, fertilizers, food preservatives, detergents, etc.
  • Industrial processes like petrochemicals, metallurgy, and polymers.
  • Environmental studies — ozone depletion, greenhouse effect, etc.

2. Laws of Chemical Combination

(i) Law of Conservation of Mass

• Mass can neither be created nor destroyed during a chemical reaction.
• Total mass of reactants = Total mass of products.
  Example:
  H₂ + Cl₂ → 2HCl
  (Mass of H₂ + Cl₂ = Mass of 2HCl)

(ii) Law of Definite Proportions

• A chemical compound always contains the same elements in the same fixed ratio by mass.
  Example:
  Water (H₂O) → H:O = 1:8 by mass.

(iii) Law of Multiple Proportions

• When two elements combine to form more than one compound, the masses of one element that combine with a fixed mass of the other are in simple whole-number ratios.
  Example:
  CO and CO₂ → Oxygen masses ratio = 1:2.

(iv) Law of Gaseous Volumes (Gay-Lussac’s Law)

• Gases react together in simple whole-number ratios by volume under similar conditions of temperature and pressure.
  Example:
  H₂ + Cl₂ → 2HCl
  (1 volume + 1 volume → 2 volumes)

(v) Avogadro’s Law

• Equal volumes of gases at the same temperature and pressure contain equal numbers of molecules.

3. Dalton’s Atomic Theory

• All matter is made up of indivisible particles called atoms.
• Atoms of the same element are identical in mass and properties.
• Atoms cannot be created or destroyed.
• Compounds are formed by the chemical combination of atoms in fixed ratios.
• Chemical reactions involve rearrangement of atoms.

4. Mole Concept and Molar Mass

Mole

• 1 mole = 6.022 × 10²³ particles (Avogadro’s number).
• It represents atoms, molecules, ions, or electrons.

Molar Mass

• The mass of one mole of a substance.
• Units: g/mol
  Example:
  • 1 mole H₂O = 18 g
  • 1 mole O₂ = 32 g

Number of moles (n):

n=Given mass (g)/ Molar mass (g/mol)

Chemistry Mid-Term Paper 2025 Class 11

5. Empirical and Molecular Formula

• Empirical formula: Shows the simplest whole-number ratio of atoms in a compound.
• Molecular formula: Shows the actual number of atoms in one molecule.

Relationship: Molecular formula=(Empirical formula)n\text{Molecular formula} = (\text{Empirical formula})_nMolecular formula=(Empirical formula)n​

where n=Molar mass/Empirical formula mass

Example:
Empirical formula = CH₂
Molar mass = 56
Empirical formula mass = 14
⇒ n = 4
⇒ Molecular formula = C₄H₈

6. Stoichiometry and Limiting Reagent

Stoichiometry

• It deals with quantitative relationships between reactants and products in a chemical reaction.

Example: 2H₂+O₂→2H₂O

• 2 moles of H₂ react with 1 mole of O₂ to form 2 moles of H₂O.

Limiting Reagent

• The reactant that is completely consumed first and limits the amount of product formed.

Example:
If 5 mol H₂ react with 2 mol O₂:
According to reaction, 2 mol H₂ needs 1 mol O₂.
For 5 mol H₂, O₂ required = 2.5 mol.
Available O₂ = 2 mol → Limiting reagent = O₂.

7. Percentage Composition

Percentage of element=Mass of element in 1 mol compound/Molar mass of compound×100

Example:
Find % of H and O in H₂O.
Molar mass = 18 g
H = 2 g, O = 16 g
%H = (2/18) × 100 = 11.11%
%O = (16/18) × 100 = 88.89%

Read more : CHEMISTRY NOTES PDF