Gas Laws

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# Gas Laws - PowerPoint PPT Presentation

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

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
• Ideal gas law
• Dalton’s law of partial pressure
• Gas Laws
Gases can be characterized by their
• Volume ( V )
• Temperature ( T )
• Number of moles ( n )
• Pressure ( P )
• Variables Affecting Gases
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
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
Temperature is directly proportional to kinetic energy
• Kinetic energy – energy of motion
• At higher temperatures, gas particles
• Have more kinetic energy
• Move more

Ex) Volume of a gas when T1 < T2

• Charles’ Law
Celsius vs. Kelvin scale
• Must use kelvin in Charles’ law calculations
• Celsius to Kelvin scale

Ex) 25 ∘C + 273 = 298 K

• Temperature Scales
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
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
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
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
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
• 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
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
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
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
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
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
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