Exam Kracker's Thermodynamics Question

[balopathic45]

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For item 96, the answer EK gave was B citing PV=nRT, and that a decrease in volume yields an increase in pressure thus pushing the reaction towards the left in favor of propane formation. However, I put D because I thought I couldn't just assume that temperature remains constant. I was under the impression that Boyle's law only held true under conditions of constant temperature.
What do you guys think?

 

[dahmsom]

imagine pushing down on a piston and this will cause a decrease in the products. Hope this help

 

[SkyJumper42]

Look at it this way, the product has a total of 7 moles and the reactants side has a total of 6 moles (Btw this ONLY applies to compounds in the gaseous phase), if you decrease volume you are obviously increasing pressure. If you are increasing pressure, imagine forcing the molecules to "stick" back together. Essentially, it will increase the side of the reaction with LESS moles of GAS, and in this case the reactants so there is less combustion of propane.

 

[balopathic45]

Look at it this way, the product has a total of 7 moles and the reactants side has a total of 6 moles (Btw this ONLY applies to compounds in the gaseous phase), if you decrease volume you are obviously increasing pressure. If you are increasing pressure, imagine forcing the molecules to "stick" back together. Essentially, it will increase the side of the reaction with LESS moles of GAS, and in this case the reactants so there is less combustion of propane.

Yeah but does that mean we can assume constant temperature??

 

[SkyJumper42]

Yeah but does that mean we can assume constant temperature??

Yes we can unless otherwise stated. Pressure seems to always be inversely related to pressure unless they say constant pressure, which when we start looking at moles and temperature.