Can you help me with the chemistry problem on gases and fuels?

Question

A fuel composed of (CH3)2N2H2 is mixed with N2O4. The two components react according to the following reaction

 

(CH3)2N2H2+2N2O4=3N2+4H2O+2CO2(all gases).

 

If 150g of (CH3)2N2H2 reacts with excess N2O4 and the product gases are collected at 27°C in an evacuated 250mL tank, what is the partial pressure of nitrogen gas produced? What is the total total press in the tank assuming the recation has 100% yield?

Answer 1

Hi Adrianna from Decatur...hope you had a great day at school. Chemistry word problem everyone's favorite...Right? NOT!
And a gas law problem...
Anyway...I'm going to give you some hints in beginning to answer this question...but I won't do it for you because once you figure it out...you will see how to use the Gas laws. If you still have problems...contact me on Wyzant I will be glad to help.

 

Let's focus on the things we know...first of all I am assuming you have covered the 3 Gas Laws... Charles' Law, Boyle's Law and Gay Lussac's Law. Using these laws, we can then begin to solve this particular problem.

 

From the problem we know the temperature and volume are constant...we can now put them into our formulas.

 

Again...here are the hints to begin...try using the formulas and what knowledge you have...try to solve it...if you still need help...contact me on Wyzant...this is a great gas word problem...one that is very typical in high school and college general chemistry exams. Not so much on ACT or SAT exams.

Answer 2

Not sure you really need to use Charles' Law, Boyle's Law and Gay Lussac's Law.  How about using basic concepts of stoichiometry and the universal gas law.

 

(CH3)₂N₂H₂+2N₂O₄==> 3N₂+4H₂O+2CO₂(all gases).

Since there is excess N2O4, the moles of products (hence the volume of products) will be dictated by the moles of (CH3)₂N₂H₂.  So, determine that first.

150 g x 1 mole/60 g = 2.5 moles (CH3)₂N₂H₂ present

moles N₂ formed = 2.5 moles (CH3)₂N₂H₂ x 3 moles N2/1 moles (CH3)₂N₂H₂ = 7.5 moles N₂ formed

moles H2O formed = 2.5 x 4 = 10 moles H2O formed

moles CO2 formed = 2.5 x 2 = 5 moles CO2 formed

To determine pressure of each gas, you can use the universal gas law:  PV = nRT and solve for P after converting 27ºC to K and using 0.250 liters as the volume.

P = nRT/V

Calculate pressure for each gas using the appropriate n (moles) and add them all to get the total pressure.