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Combined Gas Law

Combined Gas Law. Three variables changing at once Pressure Temperature Volume. Review Kinetic Molecular Theory. Gases consist of large numbers of tiny particles that are far apart relative to their size

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Combined Gas Law

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  1. Combined Gas Law Three variables changing at once Pressure Temperature Volume

  2. Review Kinetic Molecular Theory • Gases consist of large numbers of tiny particles that are far apart relative to their size • Collisions between gas particles and between particles and container walls are elastic collisions. • Gas particles are in continuous rapid, random motion. They therefore posses kinetic energy, which is the energy of motion. • There are no forces of attraction or repulsions between gas particles. • The average kinetic energy of gas particles depends on the temperature of the gas

  3. Distinguishing Laws • Identify which two variable change, then match that to the law • Pressure and Volume => Boyle’s Law • Temperature and Volume => Charle’s Law • Temperature and Pressure => Gay-Lussac’s Law

  4. Gay-Lussac’s Law Temp Pressure Charle’s Law Boyle’s Law Volume mols

  5. DEc Temperature INC IN C IN C Volume Temperature, Pressure, andVolume changes Pressure D E C D E C

  6. Steps For Solving Gas Law Problems: • Predict whether the variable will increase or decrease • Label all known and identify unknown • Change all temperatures to Kelvin • Write the equation to be used • Identify the unknown in the equation • Rearrange equation to solve for unkown • Plug in numbers and solve equation • Check that number matches prediction

  7. Combined Gas Law Charle’s Law Boyle’s Law Gay-Lussac’s Law V = k x T V = k ÷ P P = k x T or or or V x P = k V ÷ T = k P ÷ T = k V x P ÷ T = Knew V1P1 T1 V2P2 T2 =

  8. Steps For Solving Gas Law Problems: • Predict whether the variable will increase or decrease • Label all known and identify unknown • Change all temperatures to Kelvin • Write the equation to be used • (always the combined gas law for 3 variables) • Identify the unknown in the equation • Rearrange equation to solve for unkown • Plug in numbers and solve equation • This step may be done first to reduce confusion • Check that number matches prediction

  9. Combined Gas Law Example • A sample of gas at 47oC and 1.03 atm occupies a volume of 2.20L. What volume would this gas occupy at 107oC and 0.789 atm? • Variables • P1 = 1.03 atm - P2 = 0.789 atm • V1 = 2.20 L -V2 = ? • T1 = 47oC +273 = 320K - T2 = 107oC + 273 = 380K • Combined Gas Law • P1 x V1 ÷ T1 = P2 x V2 ÷ T2 • Identify Unknown • P1 x V1 ÷ T1 = P2 x V2÷ T2 • Plug in variables • 1.03 x 2.20 ÷ 320 = 0.789 x V2 ÷ 380 • 0.00708 = 0.00207 x V2 • Solve for unknown • V2 = 0.00708 ÷ 0.00207 = 3.42L

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