Combined Gas Law
Calculator
Results
- Final volume (L)
- 1.366099
- Volume change (L)
- -0.6339
Chemistry results
| Final volume (L) | 1.366099 |
| Volume change (L) | -0.6339 |
formula-map diagram
- Final volume (L)
- 1.366099
- Volume change (L)
- -0.6339
Formula breakdown
Formula
(P₁ × V₁) ÷ T₁ = (P₂ × V₂) ÷ T₂= 1.3660992128867
Note
Simplified model: these results assume ideal behaviour (ideal gases, dilute solutions, complete reactions) and standard textbook constants. Real laboratory values vary with temperature, pressure, purity and activity coefficients. Do not rely on this for safety-critical or analytical work.
More in Chemistry
See all →Frequently asked questions
What does the combined gas law describe?+
The combined gas law merges Boyle's, Charles's, and Gay-Lussac's laws into one relationship: (P1V1)/T1 = (P2V2)/T2, describing how pressure, volume, and temperature of a fixed amount of gas relate to each other when any two of these conditions change simultaneously.
Why must temperature be in kelvin for this formula?+
Like the ideal gas law, the combined gas law relies on temperature measured from absolute zero, so using Celsius would introduce zero or negative values that break the proportional relationships in the equation. Always convert to kelvin (K = °C + 273.15) first.
How is the combined gas law different from the ideal gas law?+
The combined gas law compares two states of the same fixed amount of gas (n is constant and cancels out), while the ideal gas law (PV = nRT) calculates absolute values for pressure, volume, moles, or temperature independently. Use the combined gas law when comparing before-and-after conditions for the same gas sample.
Can I use the combined gas law if only one variable changes?+
Yes — if temperature stays constant, the law reduces to Boyle's law; if pressure stays constant, it reduces to Charles's law, since those are special cases of the same general relationship. The combined law is more general and handles cases where two or more variables change together.
What's a common setup mistake when using the combined gas law?+
Mixing up which values are the 'before' state (1) and 'after' state (2), or using inconsistent units for pressure or volume between the two states, is the most frequent error. Keep pressure in the same unit and volume in the same unit on both sides of the equation.