stoichiometry

[chemistryaddict]

These questions look simple but i just couldn't get it right ..


A container contains 3.40g ammonia gas .

(a) How many moles of ammonia molecules are there ?

number of moles = m/M

= 3.4/(14+3)

=0.2

(b) How many moles of hydrogen atoms are there ?

Not really sure about this ..

2NH3 --- 2N + 3H2

(0.2)

2 moles of NH3 react with 3 moles of hydrogen .Thus 3/2x0.2=0.3moles

(c) What volume does this amount of ammonia gas occupy at room temperature and pressure ?

0.2=V/24

v=4.8dm^3

Can someone pls check all my workings .. Thanks a lot ..

[Sonic]

These questions look simple but i just couldn't get it right ..


A container contains 3.40g ammonia gas .

(a) How many moles of ammonia molecules are there ?

number of moles = m/M

= 3.4/(14+3)

=0.2

(b) How many moles of hydrogen atoms are there ?

Not really sure about this ..

2NH3 --- 2N + 3H2

(0.2)

2 moles of NH3 react with 3 moles of hydrogen .Thus 3/2x0.2=0.3moles

(c) What volume does this amount of ammonia gas occupy at room temperature and pressure ?

0.2=V/24

v=4.8dm^3

Can someone pls check all my workings .. Thanks a lot ..

a. No problems here

b. I interpreted the question of asking how many moles of hydrogen there were in the above amount of ammonia.

As you said ammonia is NH3, this means for every mole of ammonia there are 0.25 moles of N2 and 0.75 moles of H2. In 0.2 moles you will have 0.75*0.2 = 0.15 moles

c. Any ideal gas (which we assume ammonia is for this type of calculation) occupies 22.4L of space at STP which is room temperature and pressure

[chemistryaddict]

b. I interpreted the question of asking how many moles of hydrogen there were in the above amount of ammonia.

As you said ammonia is NH3, this means for every mole of ammonia there are 0.25 moles of N2 and 0.75 moles of H2. In 0.2 moles you will have 0.75*0.2 = 0.15 moles




Thanks Sonis , i am still unsure about part B . How did you know for every mole ammonia there are 0.25 moles of N2 and 0.75 moles of H2 ?

[Sonic]

Thanks Sonis , i am still unsure about part B . How did you know for every mole ammonia there are 0.25 moles of N2 and 0.75 moles of H2 ?

That comes from the molecular formula for ammonia which is NH3 and in total we can see that there are 4 atoms in each molecule (add 1 nitrogen to 3 x 1 hydrogen)

From this it's the atomic fraction in the compound which is just a more formal way of saying that one of the 4 molecules is N so it has 25% of the atoms in a molecule and so the three hydrogens must be 75% or 3/4.

Since to move from molecules to moles we just multiply by Avogadro's number this does not affect the fraction of moles

[chemistryaddict]

That comes from the molecular formula for ammonia which is NH3 and in total we can see that there are 4 atoms in each molecule (add 1 nitrogen to 3 x 1 hydrogen)

From this it's the atomic fraction in the compound which is just a more formal way of saying that one of the 4 molecules is N so it has 25% of the atoms in a molecule and so the three hydrogens must be 75% or 3/4.

Since to move from molecules to moles we just multiply by Avogadro's number this does not affect the fraction of moles


Wow i din know it can be done that way .. thanks a lot for helping .