Question

Calculate the number of moles of hydrogen(H2) present in a 500 cm3 sample of hydrogen gas at a pressure of 760 mm Hg at 27 C.

Answer 1

Solution: The data given in the problem isP = 760mm of Hg = 1 atm V = 500cm3 T =  270C T = 27+ 273 = 300 K R = 82.1 cm3 K-1mol-1 number of moles of hydrogen (n) = ? According to ideal gas equation PV= nRT n = PV/RT = 1 atm X 500 cm3 /82.1 cm3 K-1mol-1 X 300 K n = 0.023mol

Answer 2

Answer: 0.02 moles

Explanation:

According to the ideal gas equation:

$PV=nRT$

P = Pressure of the gas = 760 mm Hg = 1 atm   (1 atm =760 mmHg )

V= Volume of the gas = $500cm^3=0.5L$    $(1L=1000cm^3)$

T= Temperature of the gas = 27°C = 300 K       (0°C = 273 K)

R= Gas constant = 0.0821 atmL/K mol

n=  moles of gas= ?

$n=\frac{PV}{RT}$

Putting in all the values, we get

$n=\frac{1\times 0.5}{0.0821\times 300}=0.02$

Thus the number of moles of hydrogen $(H_2)$ present are 0.02.