# A sample of #NH_3# gas occupies 75.0 L at STP. How many molecules is this?

##### 1 Answer

#### Explanation:

Your strategy for this problem will be to determine how many *moles* of gas you have in that volume at **STP**, then use **Avogadro's number** to find the number of *molecules* of ammonia would be found in that many moles.

**STP**, *Standard Temperature and Pressure*, conditions are defined as a temperature of

Under these conditions for pressure and temperature, **One mole** of any ideal gas occupies exactly

This means that you can use the molar volume of a gas to determine how many moles you have in

#75.0color(red)(cancel(color(black)("L"))) * "1 mole"/(22.7color(red)(cancel(color(black)("L")))) = "3.304 moles"#

Now, you know that **one mole** of any substance contains exactly

#3.304color(red)(cancel(color(black)("moles"))) * (6.022 * 10^(23)"molecules NH"_3)/(1color(red)(cancel(color(black)("mole")))) = color(green)(1.99 * 10^(24)"molecules NH"_3#