What is the Ideal Gas Law?

The Ideal Gas Law is an important equation that shows the relationship between pressure (P), volume (V), temperature (T), and the number of moles (n) of a gas.

$$PV = nRT$$

Here:

• P = Pressure (for example, in atm or Pa)
• V = Volume (for example, in liters or m³)
• n = Number of moles of the gas
• R = Gas constant (0.0821 L·atm·mol⁻¹·K⁻¹ or 8.314 J·mol⁻¹·K⁻¹)
• T = Temperature (in Kelvin)

You can rearrange the formula to solve for any variable. For example, to find moles:

$$n = \frac{PV}{RT}$$

Simple Explanation:

According to this law, if you know the pressure, volume, and temperature of a gas, you can easily find its other properties. This law explains the ideal behavior of gases — meaning it assumes that gas molecules do not interact with each other. In reality, real gases behave a little differently, but the Ideal Gas Law gives a good approximation of their behavior.

How to Use the Formula (Steps)

1. Write the pressure (P) in atm or pascal (Pa).
2. Write the volume (V) in liters or cubic meters (m³).
3. Convert the temperature (T) into Kelvin (K).
4. Rearrange the formula to find moles (n) or any unknown quantity:

$$n = \frac{PV}{RT}$$

Just put the values into the formula — the calculator will instantly give you the answer!

Example

Suppose you have a gas with pressure = 2 atm, volume = 5 L, and temperature = 300 K.

Then, the calculation of moles will be:

$$n = \frac{PV}{RT} = \frac{(2)(5)}{(0.0821)(300)} = 0.406 \text{ mol}$$

So, the number of moles in the gas is 0.406 mol.

Useful Tips

• Always take the temperature in Kelvin (K), not in °C.
• Make sure the pressure and volume are in the same unit system.
• The Ideal Gas Law is an approximation — real gases show small deviations, especially at high pressure or low temperature.

Frequently Asked Questions (FAQ)

1. What is the Ideal Gas Law?

The Ideal Gas Law is a formula that shows the relationship between pressure, volume, temperature, and number of moles of a gas. The equation is PV = nRT.

2. What does R represent in the Ideal Gas Law?

R is the gas constant. Its value is 0.0821 L·atm/mol·K or 8.314 J/mol·K depending on the units used.

3. Why is temperature taken in Kelvin?

Temperature must be in Kelvin because the Ideal Gas Law works only with absolute temperature. Celsius values can give incorrect results.

4. Is the Ideal Gas Law accurate for all gases?

The Ideal Gas Law gives close results for most gases under normal conditions, but real gases show slight deviations at high pressure or low temperature.