How is Pressure Calculated in a Chemical Reaction Using the Ideal Gas Law?

[Jules18]

2 SO2 +O2 --> 2 SO3

A mixture of gases containing 0.20 mol of SO2 and 0.2 mol of O2 in a 4.0 L flask reacts to form SO3. If the temperature is 25ºC, what is the pressure in the flask after reaction is complete?

The answer key says the answer is 0.3(0.082)(298)/4, using PV = nRT. (0.3 being the number of moles of gas after the reaction.)
But according to the coefficients in the reaction, I thought since there are 0.2 moles of SO2 there should also be 0.2 moles of SO3.

Is it a typo or am I wrong in how I approached the question?

 

[Borek]

This is a limiting reagent problem...

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[Jules18]

If I understand you correctly, I knew that, and I thought the limiting reactant was SO2. So I thought that if there were 0.2 moles of SO2, there would be 0.2 moles of the product...
That was my logic

?

 

[Borek]

Correct logic so far.

If SO₂ is a limiting reagent, what can you tell about oxygen?

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[Jules18]

Ooooooookay I can't believe I didn't realize that!

grrr