You have a 5-liter container with 2.00 x 1023 molecules of ammonia gas (NH3) at STP. How many molecules of argon gas (Ar) are in an identical container at the same temperature and pressure?

A. 6.02 x 1024 molecules

B. 1.30 x 1024 molecules

C. 2.00 x 1023 molecules

D. 6.02 1023 molecules

C. 2.00 x 1023 molecules

Explanation:

Given, the pressure, volume and temperature are same in both cases.

From the ideal gas equation,

P V = n R T

where n = no. of moles = given weight : atomic weight

And 6.023 x 10^23 molecules of ammonia (NH3), weigh 17g (14 + 3 (1))

So we have

P V = ((2.00 x 10^23) / (6.023 x 10^23)) x R T

Similarly, say n molecules of argon gas (Ar) are in an identical container.

So the gas equation would be

P V = (n / 6.023 x 10^23) x R T

Because, atomic weight of Argon is beared by 6.023 x 10^23 molecules.

dividing these two equations, we get

n = 2.00 x 10^23 molecules