# 8.5 The Combined Gas Law - cbafaculty.org

8.5 The Combined Gas Law Under water, the pressure on a diver is greater than the atmospheric pressure. The combined gas law comes from the pressurevolumetemperature relationships for gases that we have studied. Learning Goal Use the combined gas law to calculate the final pressure, volume, or temperature of a gas when changes in two of these properties are given and the amount of gas is constant. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake 2016 Pearson Education, Inc. The Combined Gas Law

The combined gas law uses the pressurevolume temperature relationships from Boyles law, Charless law, and Gay-Lussacs law where n is constant. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake 2016 Pearson Education, Inc. Calculations Using Combined Gas Law A gas has a volume of 675 mL at 35 C and 646 mmHg pressure. What is the volume (mL) of the gas at 95 C and a pressure of 802 mmHg (n is constant)? STEP 1 Organize the data into a table of initial and final conditions. ANALYZE Conditions 1 Conditions 2 THE

P1 = 646 mmHg P2 = 802 mmHg PROBLEM V1 = 675 mL V2 = ? T1 = 35 C + 273 T2 = 95 C + 273 = 308 K = 178 K Moles of gas remain the same. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake 2016 Pearson Education, Inc. Calculations Using Combined Gas Law STEP 2 Rearrange to solve for unknown quantity V2.

STEP 3 Substitute the values into the gas law equation and calculate. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake 2016 Pearson Education, Inc. Study Check A sample of helium gas has a volume of 0.180 L, a pressure of 0.800 atm, and a temperature of 29 C. At what temperature (C) will the helium have a volume of 90.0 mL and a pressure of 3.20 atm (n remains constant)?

General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake 2016 Pearson Education, Inc. Solution A sample of helium gas has a volume of 0.180 L, a pressure of 0.800 atm, and a temperature of 29 C. At what temperature (C) will the helium have a volume of 90.0 mL and a pressure of 3.20 atm (n remains constant)? STEP 1 Organize the data into a table of initial and final conditions. ANALYZE THE PROBLEM Conditions 1

P1 = 0.800 atm V1 = 0.180 L (180 mL) T1 = 29 C + 273 = 302 K Conditions 2 P2 = 3.20 atm V2 = 90.0 mL T2 = ? Moles of gas remain the same. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake 2016 Pearson Education, Inc. Solution A sample of helium gas has a volume of 0.180 L, a pressure of

0.800 atm, and a temperature of 29 C. At what temperature (C) will the helium have a volume of 90.0 mL and a pressure of 3.20 atm (n remains constant)? STEP 2 Rearrange to solve for unknown quantity T2. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake 2016 Pearson Education, Inc. Solution A sample of helium gas has a volume of 0.180 L, a pressure of 0.800 atm, and a temperature of 29 C. At what temperature (C) will the helium have a volume of 90.0 mL and a pressure of 3.20 atm (n remains constant)?

STEP 3 Substitute the values into the gas law equation and calculate. - General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake 2016 Pearson Education, Inc.

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