Question

what is the final pressure (in Torr) if the temperature rises to 124.0 degrees Celcius?

Chapter 2 Question 25 Parameterization Sodium metal reacts with molecular fluorine gas to form sodium fluoride. A closed container of volume 2.00 x 10 ml contains fluorine gas at 46.0 °C and 4.39 x 10 Torr. Then 7.24 g of solid sodium is introduced, and the reaction goes to completion. What is the final pressure (in Torr) of the temperature rises to 124.0 °C? Tom

Answer 1

Step 1: Calculation of initial number of moles of Fluorine gas.

According to the Ideal gas equation

PV = nRT

n = PV/RT. (Given P = 4.39 X 10³ torr; V = 2 L; T = 46 + 273 = 319k; and R = 62.39 L.mm/k.mol)

n = 4.39 X 10³ X 2 / 62.39 X 319

n = 0.4411 mole.

Step 2 : Calculation of the number of moles of Sodium.

number of moles of sodium = Given mass of sodium/Atomic mass of sodium.

number of moles of sodium = 7.24/23

= 0.3147 mole.

Step 3: Finding the limiting reagent

2Na + F_{​​​​​​2}​​​​​ ---------> 2NaF

2 moles of Sodium can react with, one mole of Fluorine, then

0.3147 moles of sodium react with, ------------- number of moles of Fluorine.

Number of moles of Fluorine =0.3147 /2

= 0.1573 moles.

This, suggests that Fluorine gas is in excess, and hence Sodium is the limiting reagent.

Step 4: Calculation of the remaining number of moles of Fluorine gas.

Number of moles of un reacted Fluorine = 0.4411 - 0.1573

= 0.2838 moles.

( Since NaF is a solid, it can not exert any pressure, the pressure comes only from un reacted Fluorine gas).

Step 5: Calculation of final pressure

According to Ideal gas equation

PV = nRT

P = nRT/V

P = 0.2838 X 62.39 X 397/ 2

P = 3514.69 torr. (Or) 3.514 X 10³ torr.