Understanding Pressure

Although the SI unit for pressure is the Pascal, most professors use atm, mmHg or torrs as the everyday units for pressure. 

The conversion of units of pressure may sometimes be required in order to answer a quantitative question. 

Example: A geochemist heats a limestone (CaCO3) sample and collects the CO2 released in an evacuated flask. The CO2 pressure is 278.1 mmHg. Calculate the CO2 pressure in torrs and atmospheres.


The conversion of units of pressure is simply a dimensional analysis question. Recall the dimensional analysis relationships been volume and length.  

Problem: If the barometer in a laboratory reads 34.2 inHg what is the pressure in bars? (1 in = 2.54 cm)