How many atoms of Ar gas are present in a 340 mL container at 55^$\circ$C and 720 mmHg A) 0.012 Ar atoms B) 7.2 x 10²¹ Ar atoms C) 4.3 x 10²² Ar atoms D) 2.9 x 10²³ Ar atoms E) 1.7 x 10²⁴ Ar atoms

Question

Quizplus · Accepted Answer

We can use the ideal gas law to calculate the number of moles of Ar present in the container, and then use Avogadro's number to convert the moles to number of atoms.

PV = nRT

P = 720 mmHg = 0.947 atm (using conversion factor 1 atm = 760 mmHg)
V = 340 mL = 0.34 L
T = (55+273.15) K = 328.15 K
R = 0.08206 L·atm/(mol·K)

n = PV/(RT) = (0.947 atm)(0.34 L)/(0.08206 L·atm/(mol·K))(328.15 K) = 0.0144 mol

Number of atoms = n x Avogadro's number = (0.0144 mol)(6.022 x 10^23 atoms/mol) = 8.67 x 10^21 atoms, which is closest to choice C (4.3 x 10^22 atoms).

How Many Atoms of Ar Gas Are Present in a 340