# The root-mean-square speed of a gas is found to be 391.2 m/s at 270 K. The gas is ?

##### 1 Answer

Your gas is any gas that has a molar mass of approximately **44 g/mol**. The usual suspects are carbon dioxide, or

The mathematical expression for the root-mean-square is

Two important things to keep in mind for this equation - *Joules per mol K* and the molar mass of the gas is expressed in *kg per mole*, instead of in *g per mole*.

So, in order to identify the gas, you must determine its molar mass. Use the above equation to solve for

Plug in your values and solve for

Use the fact that

Transform this value into a more familiar one

Therefore, your unknown gas has a molar mass of approximately