How many molecules of nitrogen dioxide gas (NO2) are present in 15 liters of the gas at STP?

4.031×

Explanation:

You first need to calculate the number moles of NO2.  To do this use PV=nRT

STP stands for standard temperature and pressure which is 0 degrees C and 1 atm.

due to that:

P = 1 atm

V = 15 L

R = 0.08206 L*atm/mol*K

T = 273 K

n = unknown moles

solve for n to make the equation n=PV/RT

n=(1atm*15L)/(0.08206 Latm/molK*273K)

n=0.6696 mol of NO2

Then to find the number of molecules we use Avogadro's number which tells us the number of molecules per mol of a molecule or atom.

Avogadro's number is  6.02x10^23 molecules/mol

number of molecules = 0.6696mol × 6.02x10^23 molecules/mol

number of molecules = 4.031×10^23 molecules of NO2

Let me know if anything is not clear or if you get something else in the comments so that we can work it out.