Standard Temperature and Pressure Formula

STP, in Chemistry, is defined as an elementary concept. In the STP system, both temperature and pressure are in their typical form. This system's temperature and pressure are calculated to be 273K and 760 torrs, respectively. We can compute the volume of gas in STP with the help of the standard formula. The pressure is provided in torr and the temperature is given in Kelvin in this standard formula.

Formula of STP

The STP chemistry formula or STP equation is:

V$${}_{STP}$$ = V$$\frac{T_{STP}}{T}$$$$\frac{P_{STP}}{P}$$

V$${}_{STP}$$  = 30 x $$\frac{273}{350}$$ x $$\frac{1100}{760}$$

Where P$${}_{STP}$$ = 760 torr = 273K

Solved Problems

STP Problems

Let us look at a few solved problems for gas in the STP.

Problem 1

Compute the gas volume at STP whose volume is 0.5L. The temperature and pressure are 700 torrs and 300K respectively?

Answer

Given numerics are,

P = 700 torr

T = 300K

Volume of the gas = 0.5L

The formula for the volume at STP formula is given as,

V$${}_{STP}$$ = V$$\frac{T_{STP}}{T}$$$$\frac{P_{STP}}{P}$$

STP = 0.5 x $$\frac{273}{300}$$ x $$\frac{700}{760}$$

Problem 2

At 1100 Torr and 350 K the volume of a gas is given as 30L. Calculate the molar volume of a gas at STP (or) molar volume at STP formula.

Answer

The numerics, which are known to us are given as,

P = 1100 torr

T = 350K

Volume of the gas = 30L

For the volume of gas at STP formula is given as:

V$${}_{STP}$$ = V$$\frac{T_{STP}}{T}$$$$\frac{P_{STP}}{P}$$

STP = 30 x $$\frac{273}{350}$$ x $$\frac{1100}{760}$$ = 33.868L

Example

At STP, the mole of gas takes up 22.4 L. The 22.4 Liters per mole quantity is derived from the Ideal Gas Law, PV = nRT, plugging in the STP conditions for both P and T, and solving for V/n that gets 22.4 Liters per mole.

To calculate the volume of gas at STP formula or the STP calculation formula, it depends on what information that we contain:

If we have the amount of gas in moles, just multiply this particular amount by 22.4 L/mole to get the volume of the gas. For instance, if we have 2 moles of N$${}_2$$ gas, the gas will take up 44.8L.

If we have the mass of gas, we can divide the mass by the molecular weight of the gas molecules to find the number of moles. Then, multiply this result by 22.4 L/mole to get the volume. 

For example, if we have 96 g of O$${}_2$$, then we can divide by the molecular weight of O$${}_2$$ that is 32 g/mol, to get 3 moles. Then, multiply 3 moles by 22.4 L/mole, and the result is given as 67.2 Liters.

If we have a mixture of multiple gasses, then, calculate separately the volume of every component as if they were by themselves, and then add them. This happens because both temperature and pressure are held constant at STP, thus, the total volume can be conserved when mixing.