# A certain gas has a density of 1.30 g/L at STP. What will its density, in g/L, be at 546 K and 380 torr pressure ?

##### 1 Answer

The gas will have the same density at **546 K** and **380 torr** that it had at **STP**.

There are two ways to prove this - a longer one and a shorter one. Here's the longer one.

Standard Temperature and Pressure - **STP** - is defined as having a temperature of **(1)** and for the second state **(2)** (not-STP). So,

The number of moles is defined as the ratio between the gas' mass and its molar mass; plug this equation into the above one

Solve for

Density is defined as mass per unit of volume,

If you write the equation for the non-STP state, you'll get the exact same thing ,except you'll now have

This means that

In you case,

Now for the shorter answer. Notice that the *pressure drops by half* and the *temperature doubles*; if you take into account the fact that the *number of moles is constant*, the obvious conclusion is that **volume remains constant** as well.

SInce density is mass per volume, and neither mass nor volume change, then the density will be the same for both the STP and the non-STP conditions.