a 2L container is charged with 2atm of O2 at 298 Kelvin.
Ch4(g) + 2O2(g) --> CO2(g) + 2H20(g)
calculate the partial pressure of methane needed to react completely with the O2 in the vessel. What is the total pressure after the reaction is complete if the temperature increased to 750 Celcius?
Responses
AP chem - DrBob222, Saturday, April 11, 2009 at 11:54pm
Use PV = nRT
You know P, V, R, and T, calculate n for oxygen.
That allows you to calculate CH4 moles and from there moles CO2 and moles H2O.
Then calculate total P from new conditions for PV = nRT.
NEW:
once I have calculated the number of moles, how do i calculate the partial pressure of methane needed to completely react with O2? is that the number of moles?
I have you need .0817 moles of methane but i don't know if this is the same as partial pressure
Responses
ap chem repost - DrBob222, Sunday, April 12, 2009 at 8:20pm
No, moles isn't the same thing as partial pressure. I obtained an answer of 0.0818 moles CH4 needed.
Now use PV = nRT again.
You know V, R, n, and T (but T is different at the new conditions); calculate P of CH4 and that will be the partial pressure of CH4. (By the way, note the correct spelling of Celsius.)
I got 3.44 atm for the partial pressure of methane, then to get the total pressure after the reaction is complete if the temperature has increased to 750C, do I add up the moles and plug this in for n in PV=nRT?
Thank you
Yes and no. You add the moles CO2 to moles H2O and use that for n but there should be no CH4 or O2 remaining if all of the CH4 and O2 have reacted. Moles H2O will be twice that of CO2.
To calculate the partial pressure of methane needed to completely react with the O2 in the vessel, you have already calculated the number of moles of methane needed, which is 0.0818 moles.
To find the partial pressure of methane, you can use the formula PV = nRT. You know the volume (2L), the gas constant R (0.0821 L*atm/mol*K), and the temperature (298 K).
Now, rearrange the formula to solve for pressure (P): P = nRT/V.
Substitute the values into the equation: P = (0.0818 moles) * (0.0821 L*atm/mol*K) * (298 K) / (2 L).
Calculating this, you will find that the partial pressure of methane needed is approximately 1.348 atm.
To calculate the total pressure after the reaction is complete, you need to consider the new temperature of 750 degrees Celsius.
First, convert the temperature to Kelvin by adding 273: 750°C + 273 = 1023 K.
Now, use the formula PV = nRT again. But this time, you will use the new temperature (1023 K) and solve for the total pressure.
Plug in the known values: P * 2 L = (0.0818 moles + moles of CO2 + 2 * moles of H2O) * (0.0821 L*atm/mol*K) * (1023 K).
Since you don't have the exact number of moles of CO2 and H2O, you will need to calculate them first.
Using the balanced chemical equation: CH4(g) + 2O2(g) --> CO2(g) + 2H2O(g), the ratio of moles is 1:1 for CH4 and CO2. So, the moles of CO2 will also be 0.0818 moles.
From the same equation, the ratio of moles between CH4 and H2O is 1:2. So, the moles of H2O will be 2 times the moles of CH4, which is 2 * 0.0818 moles = 0.1636 moles.
Now, plug in these values into the equation: P * 2 L = (0.0818 moles + 0.0818 moles + 0.1636 moles) * (0.0821 L*atm/mol*K) * (1023 K).
Finally, solve for P: P = (0.0818 moles + 0.0818 moles + 0.1636 moles) * (0.0821 L*atm/mol*K) * (1023 K) / (2 L).
Calculating this, you will find the total pressure after the reaction is complete at 750 degrees Celsius is approximately 21.01 atm.