Question

What is the conversion of 125 mm Hg into atm?

Answer 1

Hint: There are many units in which pressure of a gas is measured such as Pascal, mm Hg, atm etc. Each unit is interconvertible to the other. The formula relating the unit of Pascal, mm Hg and atm is given below:
\[1\text{ atm}=101325\text{ Pa}=760\text{ mmHg}\]

Complete answer:
Gases have no definite shape or volume. When they are inserted to a container, the gas molecules move in random directions and exert pressure on the container walls.
Pressure is defined as a force applied to a unit surface area.
\[\text{Pressure}=\dfrac{\text{F}}{\text{A}}\]
where F and A are force per area perpendicular to the surface.
The unit of pressure in the SI system is the pascal (Pa), and it is defined as the force of one newton per square meter:
\[1\text{Pa}=1\text{N}{{\text{m}}^{-2}}\]
A pascal is a very small amount of pressure, so the more useful unit for everyday gas pressures is the kilopascal (kPa). A kilopascal is equal to 1000 pascals.
There are total three different units of pressure used in chemistry –
-Pascal (Pa)
-mm of Hg
-atmosphere (atm)
However, it is more common to express pressures in units of atmospheres or mm Hg.
\[1\text{ atm}=760\text{ mmHg}\]
Using this relation, we can convert 125 mm Hg into atm as follows:
\[\begin{align}
  & \because 1\text{ atm}=760\text{ mmHg} \\
 & \Rightarrow 1\text{ mmHg =}\dfrac{1}{760}\text{ atm} \\
 & \therefore 125\text{ mmHg =}\dfrac{125}{760}\text{ }=\text{0}\text{.164 atm} \\
\end{align}\]
Millimetres of mercury (mm Hg), is defined as a one-millimetre difference in the height of a mercury barometer at 0°C. Barometer is a device used to measure the air pressure.

Note:
Another unit of pressure used is bar. When performing pressure calculations, it is important to ensure that all dimensions are in the same unit system.