You have already seen that scientists use moles, temperature, and volume to measure matter. Another measurement, pressure, is also necessary for describing a sample of gas. Pressure is defined as the force per area on a surface.
If you have ever squeezed an inflated balloon, you have felt the pressure that the gas inside the balloon exerts. The pressure of a gas is due to the collisions of the moving gas particles with surfaces such as the walls of the balloon.
The SI unit of pressure is the Pascal (Pa), which is defined as one newton per square meter(N/m2).
However, chemists most often use units of atmospheres (atm) or millimeters of mercury (mm Hg) to measure pressure. (Millimeters of mercury are also known as torr, in honor of Evangelista Toricelli, the inventor of the mercury barometer.)
Each day you deal with money. You know the value of a dollar, a quarter, a dime, a penny, etc : Four quarters make a dollar; Ten pennies make a dime. You make conversions instinctually as you reach into your wallet to pay for things.
In chemistry and science, we do the same. However, information is shared with others