Consider the following reaction in a closed reaction flask. if 1.20 atm of gas a is allowed to react with 1.20 atm of gas b and the reaction goes to completion at constant temperature and volume, what is the total pressure in the reaction flask at the end of the reaction? 2 a(g) + 3 b(g) → a2b3(g)

The total pressure is 0.8 atm

Explanation:

Step 1: The balanced equation

2 A(g) + 3 B(g) → A2B3 (g)

This means that for 2 moles of A consumed, we need 3 moles of B to produce 1 mole of A2B3

Initial pressure of A = 1.20 atm

Initial pressure of B = 1.20 atm

Step 2: Calculate limiting reactant and reactant in excesss

If 3 moles of B need 2 moles of A to be consumed; then 1.2 mole of B needs 0.8 moles of A.

0.8 moles of A will be consumed, this means 0.4 moles will remain.

⇒ A is in excess

B will completely react, so B is the limiting reactant

If 3 moles of B need 2 moles of A to be consumed; then 0.4 moles of A2B3 will be produced.

Step 3: Calculate the total pressure

Final pressure of A = 0 atm

Final pressure of B = (1.20 - 0.80) atm = 0.40 atm

Final pressure of A₂B₃ = 0.40 atm  

Total pressure = pressure A + pressure B + pressure A2B3 = 0 atm + 0.4 atm + 0.4 atm = 0.8 atm