Important Units of Pressure, Temperature, Volume, Energy

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Important Units of Pressure, Temperature, Volume, Energy, and Mass with Conversions

Understanding different units of pressure, temperature, volume, energy, and mass is essential in chemistry and physics. Since various measurement systems exist, conversions between these units are frequently required in scientific calculations. This post provides an overview of these units, their SI units, common conversions, and practice questions to reinforce the concepts.

1. Units of Pressure

SI Unit: Pascal (Pa)

  • 1 Pa = 1 N/m² (Newton per square meter)

Common Pressure Units and Conversions

Unit Equivalent in Pascals (Pa) Equivalent in Atmospheres (atm)
1 atm 101325 Pa 1 atm
1 bar 100000 Pa 0.9869 atm
1 mmHg (Torr) 133.322 Pa 1/760 atm
1 psi (pound per square inch) 6894.76 Pa 1/14.7 atm

Quick Conversions

  • 1 atm = 760 mmHg = 101.325 kPa = 1.01325 bar
  • 1 bar = 100 kPa
  • 1 mmHg = 133.322 Pa

2. Units of Temperature

SI Unit: Kelvin (K)

Common Temperature Units and Conversions

Unit Conversion Formula
Celsius (°C) K = °C + 273.15
Kelvin (K) °C = K - 273.15
Fahrenheit (°F) °C = (°F - 32) × 5/9
Celsius (°C) °F = (°C × 9/5) + 32

3. Units of Volume

SI Unit: Cubic Meter (m³)

Common Volume Units and Conversions

Unit Equivalent in m³ Equivalent in Liters (L)
1 m³ 1 1000 L
1 L (liter) 0.001 1 L
1 cm³ (cubic centimeter) 1 × 10⁻⁶ 1 mL
1 mL (milliliter) 1 × 10⁻⁶ 1 cm³

Quick Conversions

  • 1 L = 1000 mL = 1000 cm³
  • 1 m³ = 1000 L = 10⁶ cm³
  • 1 dm³ = 1 L

4. Units of Energy

SI Unit: Joule (J)

  • 1 J = 1 kg·m²/s²

Common Energy Units and Conversions

Unit Equivalent in Joules (J)
1 kJ (kilojoule) 1000 J
1 cal (calorie) 4.184 J
1 kcal (kilocalorie) 4184 J
1 eV (electron volt) 1.602 × 10⁻¹⁹ J

Quick Conversions

  • 1 kJ = 1000 J
  • 1 kcal = 4.184 kJ
  • 1 eV = 1.602 × 10⁻¹⁹ J

5. Units of Mass

SI Unit: Kilogram (kg)

Common Mass Units and Conversions

Unit Equivalent in kg
1 g (gram) 0.001 kg
1 mg (milligram) 1 × 10⁻⁶ kg
1 μg (microgram) 1 × 10⁻⁹ kg
1 tonne 1000 kg
1 atomic mass unit (amu) 1.6605 × 10⁻²⁷ kg

Quick Conversions

  • 1 kg = 1000 g = 10⁶ mg
  • 1 g = 1000 mg
  • 1 amu = 1.6605 × 10⁻²⁷ kg

Practice Questions on Units and Conversions

Pressure Conversion Questions

  1. Convert 2 atm to mmHg.
  2. Convert 750 mmHg to atm.
  3. Express 1.5 bar in Pa.

Temperature Conversion Questions

  1. Convert 25°C to Kelvin.
  2. Convert 300 K to Celsius.
  3. Convert 98.6°F to Celsius.

Volume Conversion Questions

  1. Convert 2500 cm³ to liters.
  2. Convert 3.5 L to m³.
  3. How many milliliters are in 0.75 m³?

Energy Conversion Questions

  1. Convert 500 cal to Joules.
  2. Convert 5 kJ to calories.
  3. How much energy in eV is 2 × 10⁻¹⁸ J?

Mass Conversion Questions

  1. Convert 2.5 kg to grams.
  2. Convert 500 mg to kg.
  3. How many kilograms are in 5 tonnes?

Here are the answers to the practice questions on unit conversions:

Pressure Conversion Answers

  1. 2 atm to mmHg

    • 1 atm = 760 mmHg
    • 2 atm = 2 × 760 = 1520 mmHg
    • Answer: 1520 mmHg

  2. 750 mmHg to atm

    • 1 atm = 760 mmHg
    • 750 mmHg = 750 ÷ 760 = 0.9868 atm
    • Answer: 0.9868 atm

  3. 1.5 bar to Pa

    • 1 bar = 100000 Pa
    • 1.5 bar = 1.5 × 100000 = 150000 Pa
    • Answer: 150000 Pa

Temperature Conversion Answers

  1. 25°C to Kelvin

    • K = °C + 273.15
    • K = 25 + 273.15 = 298.15 K
    • Answer: 298.15 K

  2. 300 K to Celsius

    • °C = K - 273.15
    • °C = 300 - 273.15 = 26.85°C
    • Answer: 26.85°C

  3. 98.6°F to Celsius

    • °C = (°F - 32) × 5/9
    • °C = (98.6 - 32) × 5/9
    • °C = 66.6 × 5/9 = 37°C
    • Answer: 37°C

Volume Conversion Answers

  1. 2500 cm³ to liters

    • 1 cm³ = 0.001 L
    • 2500 cm³ = 2500 × 0.001 = 2.5 L
    • Answer: 2.5 L

  2. 3.5 L to cubic meters (m³)

    • 1 L = 0.001 m³
    • 3.5 L = 3.5 × 0.001 = 0.0035 m³
    • Answer: 0.0035 m³

  3. 0.75 m³ to milliliters

    • 1 m³ = 10⁶ mL
    • 0.75 m³ = 0.75 × 10⁶ = 750000 mL
    • Answer: 750000 mL

Energy Conversion Answers

  1. 500 cal to Joules

    • 1 cal = 4.184 J
    • 500 cal = 500 × 4.184 = 2092 J
    • Answer: 2092 J

  2. 5 kJ to calories

    • 1 kJ = 1000 J
    • 1 cal = 4.184 J → 1 J = 1/4.184 cal
    • 5 kJ = 5000 J
    • 5000 J × (1/4.184) = 1195.8 cal
    • Answer: 1195.8 cal

  3. 2 × 10⁻¹⁸ J to eV

    • 1 eV = 1.602 × 10⁻¹⁹ J
    • eV = (2 × 10⁻¹⁸) ÷ (1.602 × 10⁻¹⁹)
    • eV = 12.49 eV
    • Answer: 12.49 eV

Mass Conversion Answers

  1. 2.5 kg to grams

    • 1 kg = 1000 g
    • 2.5 kg = 2.5 × 1000 = 2500 g
    • Answer: 2500 g

  2. 500 mg to kg

    • 1 mg = 10⁻³ g, 1 g = 10⁻³ kg
    • 500 mg = 500 × 10⁻³ g = 0.5 g
    • 0.5 g = 0.5 × 10⁻³ kg = 5 × 10⁻⁴ kg
    • Answer: 5 × 10⁻⁴ kg (or 0.0005 kg)

  3. 5 tonnes to kg

    • 1 tonne = 1000 kg
    • 5 tonnes = 5 × 1000 = 5000 kg
    • Answer: 5000 kg


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