Question

Carbon monoxide at a pressure of 1490 mmHg reacts completely with O2 at a pressure of 745 mmHg in a sealed vessel to produce CO2. What is the final pressure in the flask?
2CO2 (g) + O2 (g) -> 2CO2 (g)

I thought it was just a simple addition, but it was wrong.

Answer 1

First, redo your equation.
................2CO(g) + O2(g) ==> 2CO2(g)
I...............1490.........745.............0
C............-1490........-745............1490
E.................0..............0..............1490

Answer 2

Just a different perspective. :-)
...............2CO(g) + O2(g) ==> 2CO2(g)
I...............1490.........745.............0
C...............-2x...........-x..............2x
E.................0.............0..............2x
Complete Rxn => 745 + (-x) = 0 => x = 745 mmHg
P(CO2) = 2X = 2(745 mmHg) = 1490 mmHg