catalyst question (1 Viewer)

[googleplex]

What is the end all definition of a catalyst? Conc acids are used to speed up the rate of reaction/lower activation energy/increase rate of reaction both ways in equilibrium, but surely if conc acids are dehydrating agents then they are actually getting involved in the equlibrium, e.g. favouring the formation of an ester

Is the conc acid technically a catalyst if it is a dehydrating agent? Am I missing something?

(BTW I was told that the addition of such a small amount of conc acid (5-10 drops) to the esterification process wouldn't be sufficient to dehydrate)

thx

 

[mervvyn]

What is the end all definition of a catalyst? Conc acids are used to speed up the rate of reaction/lower activation energy/increase rate of reaction both ways in equilibrium, but surely if conc acids are dehydrating agents then they are actually getting involved in the equlibrium, e.g. favouring the formation of an ester

Is the conc acid technically a catalyst if it is a dehydrating agent? Am I missing something?

(BTW I was told that the addition of such a small amount of conc acid (5-10 drops) to the esterification process wouldn't be sufficient to dehydrate)

thx

A catalyst is a substance that provides an alternate, lower energy path for the reaction to occur on. As a result, the number of particles with sufficient energy to react is increased (ie activation energy is lowered), and thus the reaction rate increases; in an equilibrium, a catalyst will not change the equilibrium position but it makes the system more easily manipulated by other factors. A catalyst is not consumed in the reaction.

With regards to esters, the conc sulfuric is a catalyst because it speeds up the rate of the reaction. The fact that it pushes the equilibrium further to the right by absorbing water, is something of a happy coincedence (so i was told).

 

[Tommy_Lamp]

The catalyst definition that mervvyn said is correct, but in regards to esterification, conc. H2SO4 is used because it is a catalyst and a de-hydrating agent (i.e. it removes water). Its best to use the correct terminology

 

[steph@nie]

What is the end all definition of a catalyst? Conc acids are used to speed up the rate of reaction/lower activation energy/increase rate of reaction both ways in equilibrium, but surely if conc acids are dehydrating agents then they are actually getting involved in the equlibrium, e.g. favouring the formation of an ester

Is the conc acid technically a catalyst if it is a dehydrating agent? Am I missing something?

(BTW I was told that the addition of such a small amount of conc acid (5-10 drops) to the esterification process wouldn't be sufficient to dehydrate)

thx

Something is not a true catalyst if it are incorporated into the final product, like peroxide isn't a true catalyst because it is incorporated into LDPE.

Because the conc sulfuric acid isn't incorporated into the ester, it's still a catalyst. The fact that it is a dehydrating agent, like tommy and mervyyn have said, just makes it more useful.

 

[tennille]

It is a catalyst because it increases the reaction rate- that is the purpose of a catalyst.

 

[googleplex]

Yes but isn't part of le chateliers principle that catalyst do not favour equilibrium one way or the other

 

[tennille]

The syllabus point states- describe the purpose of using acid in esterification for catalysis

* Esterification is catalysed by the addition of a small amount of acid. Esterification is called a condensation reaction because a water molecule condenses out.

* Only a few drops of concentrated acid needs to be added to a mixture of alkanol and alkanoic acid to catalyse the reaction.

* If concentrated sulfuric acid is added in large amounts, say 5% to 10% of the reaction volume, it can have a significant effect on the position of equilibrium. Concentrated sulfuric acid is a dehydrating agent, that is, it has a strong affinity for water. If a significant amount of sulfuric acid is present, it will shift the equilibrium position to the right by absorbing water.

alcohol + acid <--> ester + water

This increases the yield of ester. However using large amounts of sulfuric acid is wasteful, uneconomic and complicates the separation of ester from the reaction mixture.

This is from http://hsc.csu.edu.au/chemistry/core/acidic/chem935/chem935net.html#net4.

If you add only a little bit of H2SO4, then it won't effect the equilibrium.

 

[jumb]

alcohol + acid ester + water

What the hell?

I think you mean: Alcohol + Alkonoic acid <> Ester + water

 

[tennille]

Sorry, i just copied and pasted that from hsc.csu.edu.au and it musn't have accepted the reversible arrows.

 

[jumb]

Sorry, i just copied and pasted that from hsc.csu.edu.au and it musn't have accepted the reversible arrows.

Oh i see now! I was starting to wonder what an ester acid was.

 

[tennille]

hehehe...I am so sick of chem!!!