Question

How many liters of NH3, at STP, will react with 19.5 g O2 to form NO and H2O?

Answer 1

10.9 L

Step-by-step explanation:

Let's begin by introducing the strategy to solve this problem:

• Write a chemical reaction and make sure it's balanced;
• Identify STP (standard temperature and pressure, that is, T = 273.15 K and p = 1.00 atm);
• Find moles of oxygen;
• From the stoichiometry of the equation, identify the number of moles of ammonia;
• Convert moles of ammonia into volume using the ideal gas law pV = nRT.

(a) The first step is already fulfilled: the reaction is balanced and it shows that 4 moles of ammonia react with 5 moles of oxygen.

(b) Given the following variables:

`p=1.00 atm\\T=273.15 K\\m_O_2=19.5 g\\R=0.08206 (L\cdot atm)/(mol\cdot K)`

(c) Find moles of oxygen dividing mass of oxygen by its molar mass:

`n_O_2=(m_O_2)/(M_O_2)`

Here molar mass of oxygen is:

`M_O_2=32.00 g/mol`

(d) From stoichiometry, dividing moles of ammonia by its stoichiometric coefficient would be equal to the ratio of moles of oxygen divided by its stoichiometric coefficient:

`(n_(NH_3))/(4) =(n_O_2)/(5)`

Rearrange the equation to obtain moles of ammonia:

`n_(NH_3)=(4)/(5) n_O_2`

(e) Solve pV = nRT for volume of ammonia:

`pV_(NH_3)=n_(NH_3)RT\\\therefore V_(NH_3)=(n_(NH_3)RT)/(p)`

`V_(NH_3)=((4)/(5)n_O_2RT )/(p) =((4m_O_2)/(5M_O_2)RT )/(p)=(4m_O_2RT)/(5pM_O_2)`

Substitute the given data to obtain the final answer!

`{V}=(4m_O_2RT)/(5pM_O_2) =(4\cdot19.5 g\cdot0.08206 (L\cdot atm)/(mol\cdot K)\cdot273.15 K )/(5\cdot 1.00 atm\cdot32.00 g/mol)= 10.9 L`