Question

2A balloon filled with helium occupies 20.0 L at 1.50 atm and 25°C. How many moles of helium will there be in the balloon at STP?

A. 22.4 moles

B. 1.12 moles

C. 0.0446 moles

D. 0.893 moles

E. 1.23 moles

F. 4.55 moles

Answer 1

• Option E. 1.23 moles

Step-by-step explanation:

1) Data:

a) V = 20.0 L

b) p = 1.50 atm

c) T = 25°C = 25 + 273.15 K = 298.15 K

d) n = ?

2) Principles and formulae:

a) The number of moles is a measure of the amount of matter (helium gas in this case). Since, the amount of matter does not change, the number of moles at the given contidtions and at STP are the same.

b) Ideal gas equation: pV = nRT

3) Solution:

• pV = nRT ⇒ n = PV / (RT)

• n = 1.50 atm × 20.0 L / (0.0821 atm-L / K-mol × 298.15 K) = 1.23 moles

So, the correct choice is E. 1.23 moles.