please explain.. (1 Viewer)

[Abtari]

can someone explain how they would explain this dotpoint. I find it confusing, because according to me the Haber process isn't about a delicate balance involving whatever, it involves a delicate balance between maximum yield and optimum reaction rate:

explain why the Haber process is based on a delicate balancing act involving reaction energy, reaction rate and equilibrium

wth is BOS on about

thanks

 

[<Stretch>]

The Haber process must have reaction energy, reaction rate and equilibrium taken into account in order to produce a high enough yield in the shortest amount of time in the least expensive method.

Reaction energy for this process is high so a suitable catalyst in needed, Iron oxide with the addition of 0.4% potassium oxide and 0.8% aluminium oxide.
This lowers the time taken for the reaction to take place.

The reaction rate may be further increased by increasing temperatures. However the process is exothermic so it will decrease the overall yield. A balance of about 400C is about right.

By increasing the pressure of the reaction vessel, equilibrium will do its bit and act against this change, lowering pressure and producing more ammonia. 250 atm is ideal. Also say that producing vessels to cope with high pressures is costly.

Hope that explains it.

 

[Abtari]

yeah i see what u mean, but its just the way they worded the dotpoint that confuses me. i would have thought it would have been a delicate balancing act involving, say, the compromise between reaction rate and reaction yield...which are influenced by factors such as temperature, pressure, catalyst.

hmmm neway thanks

 

[Dreamerish*~]

Reaction energy would be the temperature, which in turn affects the reaction rate. Equilibrium is the explanation for why it affects the rate.

It's a messy question. We had it in our trials.

 

[Looking Glass]

Can anybody clarify exactly what the difference between yield and reaction rate is for me? I'm having a bit of trouble with this.

I understand the concepts of collisions and Le Chatelier's Principle just fine, but I just can't differentiate yield and rate in my head.

There is a graph in Pathways To Chemistry that shows the impact of temperature on an exothermic reation. It shows that the higher the temperature, the lower the maximum yield. It also shows that the limit of the yield is reached faster when the temperature is higher.
Therefore am I correct in determining that reaction rate is defined by the speed at which the maximum yield is achieved?

Would it not, then, be more economically desirable (over time) to run a reaction at the lowest possible temperature? You could just wait for the maximum yield to be achieved and then sustain the reaction at this higher yield by removing the products and resupplying the reactants? Could save on heating costs, too.

In fact, if yield is the amount of product over time that one gets, how is that not determined by the rate of the reaction?

I know this isn't essential to the course, but it's really fucking with my brain.

Thanks for any help anyone could give.

 

[xiao1985]

I think you understand what yield is.

Rate is how much stuff is been produced. NOT necessarily how fast equilibirum is achieved.

So at low temperatures, you might have 1 molecule of ammonia produced per second, whereas at high temperatures you can have say 20,000 ammonia produced per second.

Also, I am thinking you are over emphasising on the yield over rate.

Let's look at this scenario: Your customer wants ammonia at $10m a tonne. At low temperatures, you can harvest 20 tonnes in 10 years. So you say to youself, ok I'm gonna wait 20 years to earn 200m. Whereas your competitor use high temperature alternative, made 1tonne in a year, and has $10m straight way.

As you can see, rate also matters, in addition to yield. Which is why there's a huge fuss about balancing yield and rate.