chemistry aqa a level help

Nitrogen and hydrogen were mixed in a 1:3 mole ratio and left to reach equilibrium in a flask at a temperature of 550 K. The equation for the reaction between nitrogen and
hydrogen is shown.
N2(g) + 3H2(g) ⇌ 2NH3(g)
When equilibrium was reached, the total pressure in the flask was 150 kPa and the
mole fraction of NH3(g) in the mixture was 0.80
Calculate the partial pressure of each gas in this equilibrium mixture.



i dont understand how for example N2 = 7.5kpa as i keep getting 75kpa

Hi there, I hope you're having a great day! I think it's due to an error in calculation somewhere.


To solve this question, you'll have to use the information provided,

"N2(g) + 3H2(g) ⇌ 2NH3(g)
When equilibrium was reached, the total pressure in the flask was 150 kPa and the
mole fraction of NH3(g) in the mixture was 0.80."


Firstly, calculate the partial pressure of ammonia by using the formula,
partial pressure of ammonia = mole fraction of ammonia x total pressure in the flask

Answer: partial pressure of ammonia is 120kPa.
Hence, we know that the partial pressure of the nitrogen and hydrogen added up would be 150kPa-120kPa, 30kPa in total.

Secondly, calculate the individual mole fractions of hydrogen and nitrogen.
Since ammonia's mole fraction is 0.8, it means, 0.8/1 moles of gas in the flask is ammonia.
Hence, from this, we know that the remaining 0.2 moles of gas are nitrogen/ hydrogen.

Using the information above...
Since we know that nitrogen and hydrogen combine in a 1:3 ratio, the mole fraction of nitrogen would be (3/4) the remaining moles of gas, (3/4)x0.2
and, the mole fraction of hydrogen would be (1/4) the remaining moles of gas, (1/4)x0.2

Then, use the formula, partial pressure of gas A = mole fraction of gas A x total pressure in the system to solve for the partial pressure of nitrogen and hydrogen.