Chemistry · 8 min read

The ideal gas law and when real gases differ

Learn how pressure, volume, temperature, and moles connect through PV = nRT.

This MayeleCalc guide explains the concept in plain language so you can use the related calculator with better context and confidence. Work through each section, review the practical example, and check the common mistakes before applying the result.

01

Four variables describe the state

The ideal gas law relates pressure, volume, amount in moles, and absolute temperature. If three are known, calculate the fourth.

02

Temperature must be absolute

Gas-law calculations use kelvins because zero kelvin is the theoretical absence of thermal motion. Add 273.15 to Celsius.

03

Choose a compatible gas constant

The numerical value and units of R must match the pressure and volume units. Unit mismatches frequently cause incorrect answers.

04

The model has limits

Real gases deviate from ideal behavior, especially at high pressure and low temperature where molecular size and forces matter.

Practical example

See the idea in action

Write concentration in moles per litre before calculating. For [H⁺] = 0.0001 mol/L, pH = −log₁₀(0.0001) = 4.

Common mistakes to avoid

  • ×Entering a concentration in the wrong unit
  • ×Forgetting that pH is logarithmic
  • ×Rounding scientific notation before completing the equation

Key takeaways

  • Units must match the formula
  • A one-unit pH change represents a tenfold concentration change
  • Record both the input precision and final result

Put the idea into practice

Open the calculator library, choose the relevant tool, and compare realistic scenarios using the method from this guide.

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