Unit 7.1: Measurements on Gases

II) (7.1) Measurements on gases: a) Volume, amount, and temperature. i) A gas expands uniformly to fill any container in which it is placed ii) The volume of a gas is the volume of its container. 1) Can be expressed in liters, cubic centimeters or cubic meters 2) 1 L = 10 3 cm 3 = m 3 iii) The amount of matter is expressed in number of moles. (n) 1) Some cases, the mass is used instead. 2) Of course, these two quantities are related by molar mass

II) (7.1) Measurements on gases: a) Volume, amount, and temperature. iv) The temperature: Ordinary Celsius is sufficient in most cases. 1) When physical behavior is involved: Use Kelvin 2) The conversion: T K = T  C v) Pressure: 1) Force per unit area 2) The unit: The Pascal, which is one Newton of force on an area of one meter squared. 3) Atmospheric pressure: Atmospheric pressure: About 10 5 Pa or 100 kilopascals (kPa) 3) Conversion for Fahrenheit to Celsius: 4)

II) (7.1) Measurements on gases: a) Volume, amount, and temperature. v) Pressure: 1) We use a mercury barometer to measure the atmospheric pressure. It looks like this: (Next slide)

The pressure exerted by the mercury column equals the atmospheric pressure. Because of this device, pressure is often expressed in millimeters of mercury or mmHg 1 atmosphere of pressure (the normal pressure) is 760 mmHg.