# Why can you calculate the total pressure of a mixture of gases by adding together the partial pressures of the component gases?

##### 1 Answer

**Partial pressures** are really just fractions of the total pressure. You can add *any* fraction together to achieve a new total, in accordance with **Dalton's Law of Partial Pressures**. So the math is valid; it's really in the measured pressures that you can go wrong.

Suppose a total pressure **ideal, inert gases**.

Then we could have a situation where the partial pressure

By summing each contributed pressure, you get the total contribution to the pressure, i.e. you get the total pressure.

**REMARKS ABOUT REAL GASES**

This works fairly well so long **as the gas itself can be assumed ideal** without losing accuracy in terms of what its volume per

But, there are characteristics that **real gases** have, and ideal gases don't:

- Some real gases are compressed more easily than an ideal gas, and those have
**smaller**volumes per#"mol"# than if they were ideal. These gases exert a**smaller**partial pressure at a given volume. - Some other real gases are harder to compress than an ideal gas, so they have
**larger**volumes per#"mol"# than if they were ideal. These gases exert a**larger**partial pressure at a given volume.

The above two points also can blend together at extreme pressure amounts, as some gases can deviate drastically from ideality depending on the pressure and temperature of the system.

**CONCLUSIONS**

As long as every gas in a system is able to be *assumed ideal*, and as long as they *don't react*, we can treat contributions to the partial pressure with approximately equal weight.