Notes About Pressure, the Ideal Gas Law, and Gas Stoichiometry

Pressure

• To learn about atmospheric pressure and how barometers work.
• To learn the various units of pressure.
• The terms torr and mm Hg are used interchangeably by chemists.
• 1 standard atmosphere = 1.000 atm  = 760.0 mm Hg = 760.0 torr
• The SI unit for pressure is the pascal (abbreviated Pa).
• 1 standard atmosphere = 101,325 Pa
• 1.000 atm
  • 760.0 mm Hg
  • 760.0 torr
  • 14.69 psi
  • 101,325 Pa

Pressure and Volume: Boyle’s Law

• To understand the law that relates the pressure and volume of a gas.
• To do calculations involving this law.
• PV=k (Pressure x Volume = a constant)
• For Boyle’s law to hold, the amount of gas (moles) must not be changed. The temperature must also be constant.
• If we know the volume of a gas at a given pressure, we can predict the new volume if the pressure is changed.

Volume and Temperature: Charles’s Law

• To learn about absolute zero.
• To learn about the law relating the volume and temperature of a sample gas at constant moles and pressure, and to do calculations involving that law.
• The volume of each gas is directly proportional to the temperature (in kelvins) and extrapolates to zero when the temperature is 0 K.
• Charles’s law in the form V1/T1=V2/T2 applies only when both the amount of gas (moles) and the pressure are constant.
• V=bT or V/T=b=constant

Volume and Moles: Avogadro’s Law

• To understand the law relating the volume and the number of moles of a sample of gas at constant temperature and pressure, and to do calculations involving this law.
• For a gas at constant temperature and pressure, the volume is directly proportional to the number of moles of gas.
• V=an or V/n=a where V is the volume of the gas, n is the number of moles, and a is the proportionality constant.

The Ideal Gas Law

• To understand the ideal gas law and use it in calculations.
• Constant n means a constant number of moles of gas.
• Universal gas constant – V=R(Tn/P)
• Ideal gas law- PV=nRT
• Always convert the temperature to the Kelvin scale and the pressure to atmospheres when applying the ideal gas law.

Gas Stoichiometry

• To understand the molar volume of an ideal gas.
• To learn the definition of STP.
• To use these concepts and the ideal gas equation.
• Remember that the molar volume of an ideal gas is 22.4 L at STP.