Converting Pressure Units

In order to understand how pressure can affect other properties of a gas, you need to know more about the different pressure units used.

There are 3 Units of Pressure we will use in chemistry:

1. Universal unit: atm (atmosphere)
2. mm Hg (millimeters of mercury)
3. Torrs (named after Torricelli, an Italian scientist)
4. FYI: SI unit is pascal (Pa)

Think of a barometer (Toricelli’s work) like a thermometer for pressure. The higher the reading on the barometer, the higher the pressure. Of course, like some thermometers, barometers use the height of mercury to relay a measurement.

Since pressure is read in millimeters of mercury, we use that as a unit : mmHg. To credit Torecelli, we also call each mmHg, a Torr.

Hence: 1 mm Hg = 1 Torr

However, the more commonly used unit for pressure is the atmosphere, or atm. So we need a way to convert between the units. Each 1 atm = 760 mmHg or 760 Torrs.

Use simple dimensional analysis and you can convert between all three units using conversion factors:

1 atm = 760 mm Hg= 760 torrs

Problem: Convert 975 mmHg to atm.