Important Units of Pressure, Temperature, Volume, Energy, and Mass
Understanding different units of measurement is the backbone of numerical problem-solving in chemistry and physics. Because various measurement systems (Metric, Imperial, SI) exist, knowing how to seamlessly convert between units is critical for exams like JEE, NEET, and board exams.
This complete guide provides an overview of essential physical quantities, their standard SI units, high-yield conversion tables, and interactive practice questions to solidify your conceptual grasp.
1. Units of Pressure
SI Unit: Pascal (Pa)
1 Pa = 1 N/m² (One Newton of force applied per square meter).
| Unit | Equivalent in Pascals (Pa) | Equivalent in Atmospheres (atm) |
|---|---|---|
| 1 atm | 101,325 Pa | 1 atm |
| 1 bar | 100,000 Pa | 0.9869 atm |
| 1 mmHg (Torr) | 133.322 Pa | 1/760 atm |
| 1 psi | 6,894.76 Pa | 1/14.7 atm |
- 1 atm = 760 mmHg = 101.325 kPa = 1.01325 bar
- 1 bar = 100 kPa
2. Units of Temperature
SI Unit: Kelvin (K)
Temperature is fundamental in thermodynamics and gas laws. Always convert to Kelvin when using the Ideal Gas Law!
| Target Unit | Conversion Formula |
|---|---|
| To Kelvin (K) | K = °C + 273.15 |
| To Celsius (°C) from K | °C = K - 273.15 |
| To Celsius (°C) from °F | °C = (°F - 32) × 5/9 |
| To Fahrenheit (°F) | °F = (°C × 9/5) + 32 |
3. Units of Volume
SI Unit: Cubic Meter (m³)
In chemistry, Liters (L) and milliliters (mL) are more commonly used in laboratory settings than cubic meters.
| Unit | Equivalent in m³ | Equivalent in Liters (L) |
|---|---|---|
| 1 m³ | 1 | 1000 L |
| 1 L (liter) | 0.001 (or 10⁻³) | 1 L |
| 1 cm³ (cc) | 1 × 10⁻⁶ | 0.001 L (1 mL) |
| 1 dm³ | 0.001 | 1 L |
- 1 L = 1000 mL = 1000 cm³
- 1 dm³ = exactly 1 L
4. Units of Energy
SI Unit: Joule (J)
1 J = 1 kg·m²/s². Energy conversions are heavily used in Thermodynamics and Atomic Structure.
| Unit | Equivalent in Joules (J) |
|---|---|
| 1 kJ (kilojoule) | 1000 J |
| 1 cal (calorie) | 4.184 J |
| 1 kcal (kilocalorie) | 4184 J (or 4.184 kJ) |
| 1 eV (electron volt) | 1.602 × 10⁻¹⁹ J |
5. Units of Mass
SI Unit: Kilogram (kg)
While kg is the SI unit, grams (g) and milligrams (mg) are standard in stoichiometric calculations.
| Unit | Equivalent in kg |
|---|---|
| 1 g (gram) | 0.001 kg (10⁻³ kg) |
| 1 mg (milligram) | 1 × 10⁻⁶ kg |
| 1 ฮผg (microgram) | 1 × 10⁻⁹ kg |
| 1 tonne | 1000 kg |
| 1 amu (atomic mass unit) | 1.6605 × 10⁻²⁷ kg |
Test Yourself: Interactive Practice Conversions
Click on the questions below to reveal the step-by-step mathematical solutions. Try calculating them on paper first!
Pressure Conversions
1. Convert 2 atm to mmHg.
- We know: 1 atm = 760 mmHg
- Therefore: 2 atm = 2 × 760 = 1520 mmHg
- Answer: 1520 mmHg
2. Convert 750 mmHg to atm.
- We know: 1 atm = 760 mmHg
- Therefore: 750 mmHg = 750 ÷ 760 = 0.9868 atm
- Answer: 0.9868 atm
3. Express 1.5 bar in Pascals (Pa).
- We know: 1 bar = 100,000 Pa
- Therefore: 1.5 bar = 1.5 × 100,000 = 150,000 Pa
- Answer: 150,000 Pa
Temperature Conversions
4. Convert 25°C to Kelvin.
- Formula: K = °C + 273.15
- Calculation: K = 25 + 273.15 = 298.15 K
- Answer: 298.15 K
5. Convert 300 K to Celsius.
- Formula: °C = K - 273.15
- Calculation: °C = 300 - 273.15 = 26.85°C
- Answer: 26.85°C
6. Convert 98.6°F to Celsius.
- Formula: °C = (°F - 32) × 5/9
- Calculation: °C = (98.6 - 32) × 5/9
- Step 2: °C = 66.6 × 5/9 = 37°C
- Answer: 37°C
Volume Conversions
7. Convert 2500 cm³ to liters.
- We know: 1 cm³ = 1 mL and 1000 mL = 1 L
- Therefore: 2500 cm³ = 2500 mL = 2.5 L
- Answer: 2.5 L
8. Convert 3.5 L to cubic meters (m³).
- We know: 1 L = 0.001 m³
- Calculation: 3.5 × 0.001 = 0.0035 m³
- Answer: 0.0035 m³
9. How many milliliters are in 0.75 m³?
- We know: 1 m³ = 1,000 L and 1 L = 1,000 mL
- Total multiplier: 1 m³ = 10⁶ mL
- Calculation: 0.75 × 10⁶ = 750,000 mL
- Answer: 750,000 mL
Energy Conversions
10. Convert 500 cal to Joules.
- We know: 1 cal = 4.184 J
- Calculation: 500 × 4.184 = 2092 J
- Answer: 2092 J
11. Convert 5 kJ to calories.
- First, convert kJ to J: 5 kJ = 5000 J
- We know: 1 cal = 4.184 J, so 1 J = 1 / 4.184 cal
- Calculation: 5000 ÷ 4.184 = 1195.02 cal
- Answer: ~1195 cal
12. How much energy in eV is 2 × 10⁻¹⁸ J?
- We know: 1 eV = 1.602 × 10⁻¹⁹ J
- Calculation: (2 × 10⁻¹⁸) ÷ (1.602 × 10⁻¹⁹)
- Step 2: (2 ÷ 1.602) × 10¹ = 1.248 × 10 = 12.48 eV
- Answer: 12.48 eV
Mass Conversions
13. Convert 2.5 kg to grams.
- We know: 1 kg = 1000 g
- Calculation: 2.5 × 1000 = 2500 g
- Answer: 2500 g
14. Convert 500 mg to kg.
- Convert mg to g: 500 mg = 0.5 g
- Convert g to kg: 0.5 g = 0.5 × 10⁻³ kg = 5 × 10⁻⁴ kg
- Answer: 5 × 10⁻⁴ kg (or 0.0005 kg)
15. How many kilograms are in 5 tonnes?
- We know: 1 tonne (metric ton) = 1000 kg
- Calculation: 5 × 1000 = 5000 kg
- Answer: 5000 kg
Next Steps: Enhance Your Prep
Unit conversions form the mathematical foundation of almost every chapter in Class 11 and 12 Physical Chemistry. Keep practicing these core ratios until they become second nature!
- ๐ฏ Chapter-wise Practice Tests
- ๐ Quick Revision Notes
- ▶️ YouTube Lectures (Hindi)
- ๐ Full Length Mock Tests
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