Thursday

April 17, 2014

April 17, 2014

Posted by **Shannon** on Monday, March 8, 2010 at 3:41pm.

- chemistry -
**DrBob222**, Monday, March 8, 2010 at 3:54pmWrite the balanced equation.

CH4 + 2O2 ==> CO2 + 2H2O

Two ways to do this:

a) brute force.

Use PV = nRT to calculate moles CH4 in the 3.00 L container. There is no P listed but you can choose a convenient one (I think 1 atm would be easy). Just remember to use the same P later.

Using the coefficients in the balanced equation convert moles CH4 to moles O2.

Now use PV = nRT again to calculate volume of O2.

b)simple approach. Only works IF both materials are gases, as in this case.

Since T and P are the same, we don't convert everything to moles. Volumes are proportional. So we reason that 3.00 L of CH4 will require (from the coefficients in the equation) twice that or 6.00 L O2. Problem finished. I really like this approach better but students sometimes are confused by it AND they sometimes use this shortcut when the shortcut is not allowed. Good luck.

- chemistry -
**Shannon**, Monday, March 8, 2010 at 4:03pmHow do I find n?

- chemistry -
**DrBob222**, Monday, March 8, 2010 at 4:20pm**The first time or the second time?**

Two ways to do this:

a) brute force.

Use PV = nRT to calculate moles CH4 in the 3.00 L container. There is no P listed but you can choose a convenient one (I think 1 atm would be easy). Just remember to use the same P later.**PV = nRT first time**

P = 1 atm

V = 3.00 L

R = 0.08206

T = 297 K

Solve for n.

n= 0.12 or close to that. You need to go through it for the actual number. And don't round until all of the problem is done.

Using the coefficients in the balanced equation convert moles CH4 to moles O2.**0.12 moles CH4 x (2 moles O2/1 mole CH4) = 0.12 x 2/1 = 0.24 moles O2. Again, you need to go through to do it exactly.**

Now use PV = nRT again to calculate volume of O2.**PV = nRT second time.**

P = 1 atm

V = ??

n = 0.24 or whatever you get exactly.

R = you know

T = 297.

Solve for V.

- chemistry -
**DrBob222**, Monday, March 8, 2010 at 4:24pmYou may have meant how to determine n for the simple way and the answer is "that's what makes it simple." You don't find n; therefore, there is no need to go through PV = nRT twice.

**Related Questions**

Chemistry - Determine the volume of methane CH4 gas needed to react completely ...

chemistry - a typical alberta home heated with natural gas assume methane CH4 (g...

ap chem - Assuming the volumes of all gases in the reaction are measured at the ...

chem repost - a 2L container is charged with 2atm of O2 at 298 Kelvin. Ch4(g) + ...

ap chem repost - a 2L container is charged with 2atm of O2 at 298 Kelvin. Ch4(g...

Stoichiometry - How many grams of oxygen are required to completely burn 85.6 ...

re-apchem post - a 2L container is charged with 2atm of O2 at 298 Kelvin. Ch4(g...

chemistry - A sample of methane gas, CH4, was collected over water at 25.0ºC and...

chemistry - How many liters of hydrogen gas can be produced if 102 grams of ...

AP chem - a 2L container is charged with 2atm of O2 at 298 Kelvin. Ch4(g) + 2O2(...