# What volume will 0.875 moles of SF4 occupy at STP?

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a)21.4 L

b)19.6 L

c)32.7 L

• If you’re told that the conditions are at STP, you automatically know that two of the quantities are T = 0ºC, or 273K and P = 101 kPa, or approximately 1 atm.

You’re given the value n in moles, so the only unknown in the equation VP = nRT is that for the volume V. Since you want the answer to result in L, it’s best to use the Gas Constant of R = 0.082057 L·atm·K^-1·mol^-1. Using the same units as those present in the Gas Constant ensure they properly cancel.

Thus,

P = 1 atm

T = 273 K

n = 0.875 mol

R = 0.082057 L·atm·K^-1·mol^-1

V = ?

Rearranging VP = nRT, we get:

V = nRT/P = (0.875)(0.082057)(273)/(1) = 19.6 L

Source(s): Ralph H. Petrucci et al. General Chemistry, Principles & Modern Applications, 9th Edition. Chapter 6, Gases; pages 178-210. Person Prentice Hall: Upper Saddle RIver, New Jersey, 2007.

ISBN 0-12-149330-2

• at STP, the Vm=22.4

The Vm is found from equation PV=nRT

Vm=V/n = RT/P

where R is 0.082, T is 273K and P is 1atm

V=n x Vm

= 0.875 x 22.4

= 19.6 L (B)

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