Question

The combustion of propane occurs when propane interacts with oxygen gas to produce water and carbon dioxide in the following reaction:
C3H8 (g) + 5O2 (g) → 3CO2 (g) + 4H2O(l)


If 2 moles of propane C3H8 (g) react at 373 K in a volume of 2.5 L, what is the pressure in the cylinder from the C3H8 (g)?

Answer 1

Answer:

• 20 atm

Explanation:

1) Data:

a) n = 2 moles

b) T = 373 K

c) V = 2.5 liter

d) P = ?

2) Chemical principles and formula

You need to calculate the pressure of the propane gas in the mixture before reacting. So, you can apply the partial pressure principle which states that each gas exerts a pressure as if it occupies the entire volume.

Thus, you just have to use the ideal gas equation: PV = nRT

3) Solution:

• PV = nRT ⇒ P = nRT / V

P = 2 mol × 0.08206 atm-liter /K-mol × 373K / 2.5 liter = 24.5 atm

Since the number of moles are reported with one significant figure, you must round your answer to one significant figure, and that is 20 atm (20 is closer to 24.5 than to 30).