75 mL of a gas is at 690 mmHg at -45°C. What will be the new volume at
STP? -

The answer to your question is   Volume 2 = 87.5 ml

Explanation:

Data

Volume 1 = V1 = 75 ml

Pressure 1 = P1 = 690 mmHg

Temperature 1 = T1 = -45°C

Volume 2 = V2 = ?

Pressure 2 = 760 mmHg

Temperature 2 = 20°C

Process

1.- Convert the temperature to °K

T1 = -45 + 273 = 228°K

T2 = 20 + 273 = 293°K

2.- Use the combined gas law to solve this problem

                  P1V1/T1 = P2V2/T2

-Solve for V2

                  V2 = (P1V1T2) / T1P2

-Substitution

                  V2 = (75 x 690 x 293) / (228 x 760)

-Simplification

                  V2 = 15162750 / 173280

-Result

                  V2 = 87.5 ml

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