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The combined gas law

When a fixed amount of gas changes state, the ratio pV/T is the same before and after. Then you can find the new pressure, volume or temperature without knowing the amount of substance.

\frac{p_1 V_1}{T_1} = \frac{p_2 V_2}{T_2}

fixed amount of gas

p_1 V_1 = p_2 V_2

Boyle's law (constant temperature)

Symbols

$p$	pressure	Pa
$V$	volume	m³
$T$	temperature	K

Example

A cylinder with 2 L of gas is compressed to 0.5 L at constant temperature:

the pressure becomes $2/0.5 = 4$ times higher.

The units only need to match on both sides, but temperature must be in kelvin.

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Part of General Chemistry: Gas laws.