Physical Chemistry

In the Haber process, ammonia is produced by passing a mixture of nitrogen andhydrogen over a catalyst: N2(g) + 3H2(g) → 2NH3(g)

a) Calculate ∆rH*, ∆rS*, ∆rG*, and K for the reaction at 298 K.

b) An industrial reactor operates at 600 K. Calculate K at this temperature, assumingheat capacities to be independent of temperature.

c) The gas flowing into the reactor has the composition ratio 3 mol H2: 1 mol N2. If themole fraction of ammonia in the exhaust gas from the reactor is 0.35, what is thetotal pressure in the reactor? (Assume that equilibrium is established in the reactorat 600 K).

Ive done the first 2 parts but am stuck on c, any ideas?

Reply 1

charco

Study Forum Helper

Original post by hannahcalista

In the Haber process, ammonia is produced by passing a mixture of nitrogen andhydrogen over a catalyst: N2(g) + 3H2(g) → 2NH3(g)

a) Calculate ∆rH*, ∆rS*, ∆rG*, and K for the reaction at 298 K.

b) An industrial reactor operates at 600 K. Calculate K at this temperature, assumingheat capacities to be independent of temperature.

Use the value of the equilibrium constant to work out the moles of each component at equilibrium ...

Now use the mole fraction of ammonia and the fact that the ratio of nitrogen to hydrogen is 1:3 to work out the mole fractions of the other two components.

Then use PV=nRT (if you have the volume of the reactor)

Reply 2

hannahcalista

Original post by charco

Thanks very much, and what if I don't have the volume of the reactor as its not in the question?

Reply 3

charco

Study Forum Helper

Original post by hannahcalista

Thanks very much, and what if I don't have the volume of the reactor as its not in the question?

If you are given neither initial pressure data nor volume data then I really can't see how you can calculate the final pressure.

Reply 4

hannahcalista

Original post by charco

If you are given neither initial pressure data nor volume data then I really can't see how you can calculate the final pressure.

Im not given either. I think it is to do with dissociation tables and alpha but This is formation...?

Reply 5

samb1234

Original post by hannahcalista

Im not given either. I think it is to do with dissociation tables and alpha but This is formation...?

Well we know that partial pressure = mole fraction x total pressure. We can work out the mole fraction of the n2 and hydrogen as we're told their ratio in the question, and then use our expression for kp to work out the total pressure.

Reply 6

hannahcalista

Original post by samb1234

Is it the mole fraction of just the starting reagents i.e. 1/4 and 3/4? and where is the expression for Kp coming from? Thanks very much

Reply 7

samb1234

Original post by hannahcalista

Is it the mole fraction of just the starting reagents i.e. 1/4 and 3/4? and where is the expression for Kp coming from? Thanks very much

Is the k you calculated in the previous part not a kp value (since all the species are gases?) i believe the mole fraction would be 1/4 and 3/4 of 0.65 (since the product is a fraction of 0.35). I may be wrong as never seen anything like this on my spec