How many moles of helium gas are present in 120 liters at STP a. 10.5 moles

b. 5.00 moles

c. 6.5 moles

d. 5.4 moles

d) n = 5.4 mol

Explanation:

Given data:

Number of moles of He = ?

Volume of He gas = 120 L

Temperature and pressure = standard

Solution:

The given problem will be solve by using general gas equation,

PV = nRT

P= Pressure

V = volume

n = number of moles

R = general gas constant = 0.0821 atm.L/ mol.K  

T = temperature in kelvin

1 atm × 120 L = n × 0.0821 atm.L/ mol.K × 273.15 K

120 atm.L = n × 22.43  atm.L/ mol

n = 120 atm.L / 22.43  atm.L/ mol

n = 5.4 mol

observation, evidence