**The significance of Universal Gas Constant (R)**

The gas constant, also known as the universal gas constant, is a physical constant that appears in an equation defining the behavior of a gas under theoretically ideal conditions.

When a mole of gas is considered it follows from equation that: PV = RT

or, **R = (PV)/T** …. ….. …. … (1)

R is called the universal gas constant or molar gas constant. It follows from equation (1) that for one mole of any gas if the pressure is P_{1}, volume is V_{1} at temperature T_{1} then at temperature T_{2} the pressure P_{2} and volume V_{2} would be such that;

**(P _{1}V_{1})/T_{1} = (P_{2}V_{2})/T_{2}**

This relation is true for known quantity of any gas.

The numerical value of R may be calculated by determining the volume occupied by 1 mole of a gas at a given pressure and a given temperature. The dimensions of R may be easily deduced from the equation (1).

**Example:** A 1.00 L flask was filled up with a gas at pressure of 751 mm Hg temperature 26°C. What volume would this gas occupy at STP?

**Solution**: The information given is as follows;

P_{1} = 751 mm Hg; P_{2} = 760 mm Hg

V_{1} = 1.00 L; V_{2} = Unknown

T_{1} = 299 K; T_{2} = 273 K

Substituting these data in equation (1) and solving for V_{2} we get,

V_{2} = (P_{1}V_{1})/T_{1} . (T_{2}/P_{2}) = [(751*1.00)/299]*(273/299) = 0.90 L