H2+pressure

[budullewraagh]

just wondering what i would end up with if i created an atmosphere with oh, say 3/4ths H2 and 1/4th air and increased pressure.

 

how much pressure would be required to form NH3?

how much pressure would be required to form H2O (i could imagine much less than the amount for NH3).

what else would be produced?

 

we can assume that not all of the H2 will form H2O because there is more H2 than the amount required to make the H2+O2 -> 2H2O reaction go to completion.

[pulkit]

You can mix hydrogen and oxygen and keep it for ages, nothing will happen untill you initiate the reaction. Pressure will govern the extent of formation (LeChatelier Principle). The kinetics of the reaction would also depend on concentration and hence pressure. So increased presssure, would mean a faster and more extensive reaction. There should be no minimum limit of pressure.

Same applies to hydrogen and nitrogen.

[budullewraagh]

i understand the principles explained above. i understand that the synth reactions for H2O and NH3 would be favored because there are less moles of gas. that is basic equilibrium. i was referring to specific calculations.

[pulkit]

how much pressure would be required to form NH3?

how much pressure would be required to form H2O

 

Why do you then think there is a minimum pressure requirement ?

Given pressure p, you'll get a certain amount of compound which is fixed and easily determined.

[budullewraagh]

there is a pressure requirement because at STP, the decomposition reaction is favored; you don't see too much NH3 or H2O gas when you release H2 gas.

[pulkit]

there is a pressure requirement because at STP, the decomposition reaction is favored

As far as I can think, if you provide enough energy to overcome the activation barrier, the reaction should take place, even if it does occur to a small extent......thats just basic equilibrium.

[budullewraagh]

right, but i'm not looking forward to making an incredibly small amount of NH3 and H2O at STP.

[pulkit]

Simple procedure :

Assume a temperature T, from that get the value of rate constant and equilibrium constant.

Then you can arrive at an expression for concentration in which ammonia and water will form as a function of p alone.

However, all this is again subject to the fact that you can somehow initiate the reaction and keep it going, spontaneity would intuitively require a very high temperature (to make free energy change just neagative). As free energy is directly linked to temperature by Gibbs-Helmholtz equation, the ideal way of achieving spontaneity would be to go on increasing temperature (endothermic reactions).