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The combined gas law has practical applications in situations where pressure, volume, or temperature can change. \[V_2 = \frac{2.44 \: \cancel{\text{atm}} \times 4.01 \: \text{L}}{1.93 \: \cancel{atm}} = 5.07 \: \text{L}\]. proportional increase in volume. \[P_2 = \frac{722 \: \text{torr} \times 88.8 \: \cancel{\text{mL}}}{663 \: \cancel{\text{mL}}} = 96.7 \: \text{torr}\]. Take pressure (P) and volume (V), for example. Refrigerants The rule is that to find the value of the unknown variable, you must mathematically isolate the unknown variable by itself and in the numerator of one side of the equation. 3. temperature of any gas.