Chapter 6: Unit 3. Gas Pressure
Gas pressure
The pressure of a gas is the force exerted when gas particles strike the surface of the walls of the container. The pressure a gas exerts on a surface, such as the walls of a container, results from the continual bombardment on the walls of the container by the rapidly moving gas molecules. We use an instrument called barometer to measure atmospheric pressure. One type of barometer consists of a long glass tube that is completely filled with mercury and then inverted into a pool of mercury in a dish. Because there is no air at the top of the mercury column inside the tube no gas pressure is exerted on the mercury column. The atmosphere, however, exerts its pressure on the mercury in the open dish. The difference in the heights of the two mercury levels is a measure of the atmospheric pressure. Pressure is measured by barometer and units are:
Atmosphere(atm), millimeter of Hg( mm Hg) , torr.
1atm= 760 torr=760 mm of Hg= 14.7 psi= 101,325 Pa
Other units of pressure are pascal, bar etc. All the units can be interconverted.
Example: On a dry day, atmospheric pressure is 734 torr. What is the pressure in atmospheric unit?
Ans: 734 torr * 1 atm = 0.966 atm
760 torr
Questions:
- A scuba diver begins diving at 3000. psi. Convert this pressure into 1) atm 2) mm of Hg.
Ans: a) 204.1 atm b) 155100 mm of Hg