CBSE · Class 7
Class 7 Science Key Concepts and Formulas
Chapter-wise important concepts, definitions, and relations for CBSE Class 7 Science
Ch 1.Heat
| Formula / Relation | Expression |
|---|---|
| Temperature conversion (°C to °F) | °F = (°C × 9/5) + 32 |
| Temperature conversion (°F to °C) | °C = (°F − 32) × 5/9 |
| Boiling point of water | 100°C = 212°F |
| Melting point of ice | 0°C = 32°F |
| Normal body temperature | 37°C = 98.6°F |
Ch 2.Acids, Bases and Salts
| Formula / Relation | Expression |
|---|---|
| pH of pure water | pH = 7 (neutral) |
| Neutralisation reaction | Acid + Base → Salt + Water |
| Common acid — Vinegar | Acetic acid (CH₃COOH) |
| Common base — Baking soda | NaHCO₃ (Sodium hydrogen carbonate) |
| Common salt | NaCl (Sodium chloride) |
Ch 3.Physical and Chemical Changes
| Formula / Relation | Expression |
|---|---|
| Rusting of iron | 4Fe + 3O₂ + 6H₂O → 4Fe(OH)₃ |
| Burning of magnesium | 2Mg + O₂ → 2MgO |
| Electrolysis of water | 2H₂O → 2H₂ + O₂ |
| Carbon dioxide test | Ca(OH)₂ + CO₂ → CaCO₃↓ + H₂O |
Ch 4.Weather, Climate and Adaptations
| Formula / Relation | Expression |
|---|---|
| Wind speed (Beaufort scale) | 0 (calm) to 12 (hurricane) |
| Humidity | Relative Humidity = (Actual water vapour / Saturation water vapour) × 100% |
| Water cycle stages | Evaporation → Condensation → Precipitation → Collection |
Ch 5.Soil
| Formula / Relation | Expression |
|---|---|
| Soil composition (average) | 45% minerals + 25% air + 25% water + 5% organic matter |
| Percolation rate | Percolation rate = Amount of water / Time |
Ch 6.Nutrition in Plants and Animals
| Formula / Relation | Expression |
|---|---|
| Photosynthesis | 6CO₂ + 6H₂O + Light energy → C₆H₁₂O₆ + 6O₂ |
| Respiration (cellular) | C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy (ATP) |
Ch 7.Motion and Time
| Formula / Relation | Expression |
|---|---|
| Speed | Speed = Distance / Time |
| Time period of pendulum (qualitative) | T depends on length of pendulum (not mass) |
| Frequency | Frequency = 1 / Time period |
Ch 8.Light
| Formula / Relation | Expression |
|---|---|
| Law of reflection | Angle of incidence = Angle of reflection |
| VIBGYOR (white light spectrum) | Violet–Indigo–Blue–Green–Yellow–Orange–Red |
Frequently Asked Questions
What are the most important chapters in Class 7 Science?
The most important chapters for exams are: Nutrition in Plants and Animals, Heat, Acids/Bases/Salts, Physical and Chemical Changes, and Motion and Time. These chapters have the highest question frequency in annual exams and unit tests.
How is Class 7 Science different from Class 6?
Class 7 Science introduces chemical reactions (acids, bases, salts, rusting), quantitative concepts (temperature formulas, speed calculations), and the water cycle in more detail. It is more conceptual than Class 6 and builds the foundation for Class 8 and 9 Science.
What is the formula for photosynthesis in Class 7?
Photosynthesis: 6CO₂ + 6H₂O + Light energy → C₆H₁₂O₆ (glucose) + 6O₂. This is the most important reaction in Class 7 Biology — learn it accurately including reactants and products.
How to remember acid-base reactions for Class 7?
Remember: Acid + Base → Salt + Water (neutralisation). Key indicators: Litmus paper turns red in acids, blue in bases. Turmeric stains turn red-brown with bases. Acids taste sour (lemon, vinegar); bases feel slippery (soap). Never taste or touch chemicals in the lab.
What is the temperature conversion formula for Class 7?
°F = (°C × 9/5) + 32 to convert Celsius to Fahrenheit. °C = (°F − 32) × 5/9 to convert Fahrenheit to Celsius. Normal body temperature is 37°C = 98.6°F — this is a commonly asked question.
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