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The Gas Laws

The Gas Laws. Problem Solving: Using Either. P 1 V 1 T 1. P 2 V 2 T 2. or. =. PV = nRT. Example Problems.

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The Gas Laws

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  1. The Gas Laws Problem Solving: Using Either P1V1 T1 P2V2 T2 or = PV = nRT

  2. Example Problems A 2.00 L bottle containing only air is sealed at a temperature of 22°C and a pressure of 0.982 atm. The bottle is placed in a freezer and allowed to cool to 3.0°C. What is the pressure in the bottle? Step 1: Decide which formula to use. P1V1 T1 P2V2 T2 = Step 2: Identify variables given & variable that is unknown. V is constant because bottle does not change. T1 = 22oC P1 = 0.982 atm T2 = 3.0oC P2 = ? atm

  3. Step 3: Convert all temperatures to KELVIN & make sure pressure units are consistent . T1 = 22+ 273 = 295K T2 = 3.0 + 273 = 276 K Step 4: Plug in all known values into equation. .982 295 P2 276 = Step 5: Solve for the Unknown (do the math!). (.982)(276) = 295P2 P2= .919atm

  4. 2) Hydrogen gas is collected by water displacement. Total volume collected is 0.461 L at a temperature of 17°C and a pressure of 751.64 mmHg. What volume of dry hydrogen gas is collected? Step 1: Decide which formula to use. P1V1 T1 P2V2 T2 = Step 2: Identify variables given & variable that is unknown. Total Volume = V1 V1 = 0.461 L Temperature is constant. P2 = must subtract water vapor pressure @ 17oC from P1 P1 = 751.64 mmHg V2 = volume of dry hydrogen = ??

  5. Step 3: Convert all temperatures to KELVIN & make sure pressure units are consistent . Not needed since temperature is constant. Step 4: Determine the water vapor pressure in atmospheres at 17oC and subtract this value from P1. P2 = 751.64 – 14.5 = 737.14 mmHg Step 5: Plug in all known values into equation. (751.64)(.461) = (737.14) V2 Step 6: Solve for the Unknown (do the math!). (751.64 x .461) 737.14 = 0.470 L

  6. 3) What pressure in atmospheres will 1.36 kg of N2O gas exert when it is compressed in a 25.0 L cylinder and is stored in an outdoor shed where the temperature can reach 59°C during the summer? Step 1: Decide which formula to use. PV = nRT Step 2: Identify variables given & variable that is unknown. Mass = 1.36 kg V = 25.0 L T = 59oC P = ?? atm R = 0.0821 L-atm/K-mol

  7. Step 3: Convert all temperatures to KELVIN & make sure pressure units are consistent . T = 59 + 273 = 332 K Step 4: Convert mass to moles. 1.36 kg N2O must be converted to moles using the molar mass of N2O Molar mass N2O: (2 x 14.01) + 15.9994 = 44.019 g/mol 1.36 kg 1000 g 1 mol = 30.9 mol 44.019 g 1 kg Step 5: Plug in all known values into equation. Make sure answer has unit of pressure required!! P (25.0) = (30.9)(.0821)(332) Step 6: Solve for the Unknown (do the math!). P = (30.9 x .0821 x 332) 25.0 P = 33.6 atm

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