Question on gasses in chemical reaction (2)?

Question

I do not understand how to do the following problem:

Nitrogen dioxide reacts with water to produce oxygen and ammonia.

4NO2(g) + 6H2O (g) → 7O2(g) + 4NH3(g)

At a temperature of 415°C and a pressure of 725 mmHg, how many grams of NH3 can be produced when 4.00 L NO2 react?

Answer bank:
a.1.25 g NH3
b.1.15 g NH3
c.6.51 g NH3
d.0.0676 g NH3
e.2.15 g NH3
f.1.91 g NH3
g.2.64 g NH3


I asked this question eairlier and someone answered:
"1) Calculate the # of moles NO2 that are in 4 L of gas.
2) The # of moles NO2 will equal the # of moles NH3 produced.
3) Convert the moles to grams and you will have your answer."

However, I do not not know how to calculate the number of moles of NO2 that are in 4 L of gas. Can someone please explain how to do this, or provide the answer. THANKS VERY MUCH.

Answer 1

Hi, you have to apply the general law for gases (.perfect gases!,
It states

p*V = n*R*T

where p is the absolute pressure, n the number of moles, R the universal gas constant and T the absolute temperature. As unit system we are using N/m^2 for pressure,
grad Kelvin (K) for temperature , m^3 for volume, J = Ws for energy and s for time.

Given: R = 8314,4 J/(kmol*K)
V = 4l = 4*10^-3 m^3
T = 273,1 + 415 = 688,1 K
p = 725 mmHg = 725*1 bar/760 mmHg =
0,954*10^5 N/m^2

The number of moles is

n = p*V/(R*T)

Just put in the numbers. Watch the units!


1Ws = 1 J
760 mmHg = 1 bar = 10^5 N/m^2
amount of gramms = n*M with M molecular weight of the substance, in case of NH3 m = 17g/mol

Answer 2

Use pV = nRT, so that n = pV/RT

You must convert the temperature to Kelvin, and the 4 litres to cubic metres, and the pressure to Pascals.