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Gas Laws

Gas Laws. Chemistry 9(A). Learning Objectives Describe the relationships between volume, pressure, number of moles, and temperature for an ideal gas Perform calculations that predict values for variables using Boyle’s law Charles’ law Avogadro’s law Ideal gas law

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Gas Laws

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  1. Gas Laws Chemistry 9(A)

  2. Learning Objectives • Describe the relationships between volume, pressure, number of moles, and temperature for an ideal gas • Perform calculations that predict values for variables using • Boyle’s law • Charles’ law • Avogadro’s law • Ideal gas law • Dalton’s law of partial pressure • Gas Laws

  3. Gases can be characterized by their • Volume ( V ) • Temperature ( T ) • Number of moles ( n ) • Pressure ( P ) • Variables Affecting Gases

  4. Gas law – law which describes the relationship between two or more variables of a gas • Variables may be directly or inversely related • Direct relationship – values of variables increase or decrease together • Inverse relationship– as the value one variable goes up, the value of the other variable goes down • Variables not included in the gas law remain constant • Gas Relationships

  5. Charles’ law describes the relationship between temperature and volume, when the pressure and amount of gas are constant • Volume and temperature are directly proportional on the Kelvin scale • Charles’ Law

  6. Temperature is directly proportional to kinetic energy • Kinetic energy – energy of motion • At higher temperatures, gas particles • Have more kinetic energy • Move more • Spread out Ex) Volume of a gas when T1 < T2 • Charles’ Law

  7. Celsius vs. Kelvin scale • Must use kelvin in Charles’ law calculations • Celsius to Kelvin scale Ex) 25 ∘C + 273 = 298 K • Temperature Scales

  8. Charles’ Law Calculation • Write unknown and givens • Identify the formula and rearrange, if needed Ex) A 2.4 L volume of gas is heated from 298 K to 405 K. What new volume does it occupy? • Convert units and find intermediates, if needed • Plug in and solve • Make sure the answer is reasonable

  9. Boyle’s law describes relationship between pressure and volume when the temperature and amount of gas remain constant • Pressure and volume are inversely proportional • Boyle’s Law

  10. Units of pressure • Atmospheres (atm) • Millimeters of mercury (mmHg) • Kilopascals (kPa) Equivalent amounts • 1 atm = 760 mmHg = 101.3 kPa Ex) How many kilopascals are equal to 5.00 atm? • Pressure Units

  11. Boyle’s Law Calculation • Write unknown and givens 2. Identify the formula and rearrange, if needed Ex) The initial pressure of a 3.0 L sample of gas was 2.5 atm. At what pressure will the volume of the gas expand to 5.0 L? • Convert units and find intermediates, if needed • Plug in and solve • Make sure the answer is reasonable

  12. Avogadro’s law describes the relationship between number of moles and volume, when temperature and pressure remain constant • Number of moles of gas are directly proportional to volume • Avogadro's Law

  13. Avogadro’s Law Calculation • Write unknown and givens • Identify the formula and rearrange, if needed Ex) How many moles of carbon monoxide gas are present in a 9.6 L sample if 4.2 moles were contained in 5.0 L sample? • Convert units and find intermediates, if needed • Plug in and solve • Make sure the answer is reasonable

  14. Combining Charles’, Boyle’s, and Avogadro’s laws gives the following equation: • A gas always has the same relationships between its variables • Charles –– volume and temperature are directly proportional • Boyle –– pressure and volume are indirectly proportional • Avogadro –– number of moles and volume are directly proportional • R is the ideal gas constant • Ideal Gas Law

  15. Ideal gas law describes the relationship between all four variables: temperature, volume, number of moles, and pressure • Potential values for Rdepending on the pressure unit used • 0.0821 = 8.31 = 62.4 • Ideal Gas Law

  16. Ideal Gas Law Calculation • Write unknown and givens • Identify the formula and rearrange, if needed Ex) What is the volume of a 1.42 mol sample of O2 gas at 25 °C and 1.25 atm of pressure? • Convert units and find intermediates, if needed • 4. Plug in and solve • Make sure the answer is reasonable

  17. Dalton’s law of partial pressure describes the relationships in a mixture of gases • Total pressure of a gas mixture is equal to the sum of the partial pressures of the individual gases • Dalton’s Law of Partial Pressure

  18. Dalton’s Law Calculation • Write unknown and givens • Identify the formula and rearrange, if needed Ex) A mixture of gases containing methane, CH4, ethane, C2H6, and propane, C3H8, gases has a total pressure of 975 mmHg. If the partial pressures of CH4 and C2H6 are 235 mmHg and 450mmHg, respectively, what is the partial pressure of C3H8 ? • Convert units and find intermediates, if needed • Plug in and solve • Make sure the answer is reasonable

  19. Learning Objectives • Describe the relationships between volume, pressure, number of moles, and temperature for an ideal gas • Perform calculations that predict values for variables using • Boyle’s law • Charles’ law • Avogadro’s law • Ideal gas law • Dalton’s law of partial pressure • Gas Laws

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