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

AI Thread Summary
The discussion centers on calculating pressure in a chemical reaction using the Ideal Gas Law, specifically for the reaction 2 SO2 + O2 --> 2 SO3. Participants analyze a scenario with 0.20 mol of SO2 and 0.20 mol of O2 in a 4.0 L flask at 25ºC, questioning the final pressure calculation after the reaction. The answer key indicates 0.3 moles of gas remain after the reaction, leading to confusion about the stoichiometry and limiting reactants. It is clarified that SO2 is the limiting reagent, which affects the amount of SO3 produced, ultimately resolving the misunderstanding about the mole quantities. Understanding the limiting reagent concept is crucial for accurately applying the Ideal Gas Law in this context.
Jules18
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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?
 
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This is a limiting reagent problem...

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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

?
 
Correct logic so far.

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

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

grrr
 
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