Chemistry Help?!?!

How many grams of methane gas (CH4) need to be combusted to produce 18.2 L water vapor at 1.2 atm and 275 K? Show all of the work used to solve this problem.

CH4 (g) + 2O2 (g) yields CO2 (g) + 2H2O (g)

Question

Chemistry Help?!?!

How many grams of methane gas (CH4) need to be combusted to produce 18.2 L water vapor at 1.2 atm and 275 K? Show all of the work used to solve this problem. 

CH4 (g) + 2O2 (g) yields CO2 (g) + 2H2O (g)

anonymous · Answer

@Cuanchi can you help me?

photon336 · Answer

You use the ideal gas equation 

$$pV = nRT $$

and then rearrange and solve for the number of moles of water. 

btw r = 0.08 

$$\frac{ pV }{ TR } = $$

anonymous · Answer

@photon336
So the equation would be n=(0.0821)*(275 K)/(1.2 atm)*(18.2 L)?

photon336 · Answer

$$(\frac{ 1.2atm*18.2L }{ 0.08~L~mol^{-1}atm~K^{-1}*275~K } )= n_{moles}$$

anonymous · Answer

@Photon336 
 So the rounded answer is 1 mole? And then what? Don't I have to multiply that by the molar mass?

photon336 · Answer

so we have 1 mole of water vapor

anonymous · Answer

Yeah. How do you find molar mass?

photon336 · Answer

now we need to go back to the balanced equation: 

now we multiply the number of moles of water by the molar ratio of the two to figure out how many moles of CH4 

$$\frac{ CH4 }{ 2H_2O }*1~Mol~H_2O = mol~?~CH_4$$

anonymous · Answer

Becuase there are 2 moles of water there should be 2 moles of CH4?

photon336 · Answer

Well that's in the balanced chemical reaction. but remember we have 1 mole of water

photon336 · Answer

and the molar ratio of CH4 to water is 1/2

photon336 · Answer

so that's why I did 



$$\frac{ CH4 }{ 2H_2O }*1~Mol~H_2O = mol~?~CH_4$$

anonymous · Answer

So it's .5?

photon336 · Answer

yep so now you need to figure out the number of grams of CH4 you need

photon336 · Answer

you know you have 0.5 moles of CH4 finding the number of grams is easy: 

1. Moles of CH4*(molar mass of CH4) = grams 

$$moles*(grams/mole) = grams $$

anonymous · Answer

Ok, I don't have the proper periodic table, but 0.5 moles of CH4 is 8? Or did I do that wrong?

photon336 · Answer

16 grams/mole

anonymous · Answer

(0.5 mol CH4) * (16 grams/mole)= 8 grams? Right?

photon336 · Answer

yes

anonymous · Answer

So 8 is the molar mass?

photon336 · Answer

16 is the molar mass in grams/mole

photon336 · Answer

when you take the product of those two you end up getting the number of grams of CH4

anonymous · Answer

oh. okay thanks for the help :D

photon336 · Answer

no problem. just remember to close out your question when you're done.