Pressure is a measure of force per unit area.
The pressure exerted by a gas sample depends on the
size of the container (volume)
number of particles colliding (amount of gas)
speed at which the particles are moving when collision occurs (and thus the temperature).
number of particles colliding (amount of gas)
speed at which the particles are moving when collision occurs (and thus the temperature).
Because the pressure due to the gases in the atmosphere keeps a column of mercury 760 mm high from falling due to gravity, pressures were traditionally expressed in atm, mm Hg or torr (after the Italian scientist Torricelli).
The SI unit of pressure is the pascal (Pa).
1 Pa equals 1 N m–2 (Newton per metre squared).
A Newton is the force exerted by a 1 kg mass falling at an acceleration of 1 m s–2.
Thus the unit for pascals is kg m s–2 × m–2 (kg m–1 s–2)
Yet another way that the unit for pascals can be expressed is J m–3. Thinking of pascals as J m–3 is VERY handy for chemists.
Thus the unit for pascals is kg m s–2 × m–2 (kg m–1 s–2)
Yet another way that the unit for pascals can be expressed is J m–3. Thinking of pascals as J m–3 is VERY handy for chemists.
The pascal is a small unit of pressure, so it is common to use kPa or bar (1 bar = 100 kPa)
The bar is a large unit of pressure. Weather forecasters use millibars to describe atmospheric pressure. Atmospheric pressures are typically in the region of 1000 millibars.