Chemistry – Basic Concepts
Prepared for MHT‑CET (B.Sc. & B.Tech.)
1. Simple Explanation
Chemistry is the science that studies the nature, composition, structure, properties, and changes that matter undergoes.
- Matter: Anything that has mass and occupies space (solid, liquid, gas).
- Elements: Pure substances made of only one type of atom (e.g., H, O, Fe).
- Compounds: Substances made of two or more elements chemically bonded (e.g., H₂O, NaCl).
- Mixtures: Physical blends of two or more components that can be separated by physical means (e.g., air, seawater).
Chemistry deals with atoms (the basic building blocks), their arrangement into molecules or ionic lattices, and the forces (chemical bonds) that hold them together.
2. Key Points (Quick Reference)
| Concept | What it is | Key Feature |
|---|---|---|
| Matter | Solid, liquid, gas, plasma | States differ by particle arrangement & motion |
| Atoms | Center (nucleus) + electrons | Nucleus: protons (Z) + neutrons; electrons in shells |
| Elements | Single‑element substances | Identified by atomic number on the periodic table |
| Compounds | Chemical combinations | Fixed empirical formula, unique properties |
| Mixtures | Physical blends | Variable composition, separable by filtration, distillation, etc. |
| Periodic Table | Organized by increasing atomic number | Groups (columns) → similar valence; Periods (rows) → principal quantum number |
| Chemical Bonding | Ionic, covalent, metallic, hydrogen, Van der Waals | Determines compound’s structure & properties |
| Reactions | Matter changes → new substances | Must obey Conservation of Mass & Energy |
| Stoichiometry | Quantitative relation between reactants & products | Moles, molar mass, mole ratio from balanced equation |
| Laws of Chemical Equilibrium | Reversibility & dynamic balance | (K_c = \frac{[C][D]^{...}}{[A][B]^{...}}) |
| Acids & Bases | (pH < 7) vs (pH > 7) | (pH = -\log[H^+]) |
| Redox | Oxidation (loss of e⁻) + reduction (gain of e⁻) | Balancing via oxidation numbers |
3. Worked Example – Stoichiometry
Problem
Calculate the mass of CO₂ produced when 5.00 g of methane (CH₄) is completely burned in excess O₂.
Solution
-
Write & balance the combustion equation
[ \text{CH}_4 + 2\text{O}_2 ;\longrightarrow; \text{CO}_2 + 2\text{H}_2\text{O} ]
-
Find moles of CH₄
[ M_{\text{CH}4} = 12.01 + 4(1.008) = 16.04\ \text{g·mol}^{-1} ] [ n{\text{CH}_4} = \frac{5.00\ \text{g}}{16.04\ \text{g·mol}^{-1}} = 0.311\ \text{mol} ]
-
Use mole ratio to get moles of CO₂
From the equation, 1 mol CH₄ → 1 mol CO₂, so
( n_{\text{CO}_2} = 0.311\ \text{mol} ) -
Convert moles of CO₂ to mass
[ M_{\text{CO}2} = 12.01 + 2(16.00) = 44.01\ \text{g·mol}^{-1} ] [ m{\text{CO}_2} = 0.311\ \text{mol} \times 44.01\ \text{g·mol}^{-1} = 13.7\ \text{g} ]
Answer: 13.7 g of CO₂ are produced.
4. Quick Revision Summary
- Matter: solids, liquids, gases, plasma.
- Atom: nucleus (protons + neutrons) + electrons.
- Element: defined by atomic number (Z).
- Compound: fixed ratio of elements; unique properties.
- Mixture: variable ratio; separable by physical means.
- Periodic Table: groups (valence similarity) & periods (energy levels).
- Bond Types: ionic (electrostatic), covalent (shared e⁻), metallic (sea of e⁻).
- Conservation Laws: mass, energy, charge.
- Stoichiometry: balanced equations → mole ratios → mass calculations.
- pH: (pH = -\log[H^+]); acids (pH<7), bases (pH>7).
- Redox: oxidation number changes; electrons transferred.
Use this cheat‑sheet as a quick refresher before the MHT‑CET exam. Good luck!