Cracking, catalyst, activation energy, equilibrium

[kenhung123]

Are these at all relevant to unit 3? Coz old exams seems to have questions on these in unit 3

[stonecold]

You need to know this:

-Cracking (thermal or catalyctic) are reactions where alkanes are reacted to form an alkane and an alkene.
-Catalyst is an inorganic substance that increases the rate of reaction by lowering the activation energy required for the reaction.  Enzymes do the same thing, but are organic, highly specific, and will only function in a narrow range of conditions.
-Activation energy is the amount for energy required to begin a chemical reaction.

I don't really get what you mean by equilibrium.  I would just use that term to describe mole ratios.
'The reaction is complete when the reactants are in equilibrium, according to the mole ratio.'

Something like that.

You should also know what catalysts are to be used depending on the reaction.
i.e. Phosphoric acid for ethene ---> ethanol
     Sulfuric acid for alkanol + carboxilic acid ---> ester + water
     etc.

[simonhu81292]

i think equilibrium is now in unit 4.. yeah it was in unit 3 back in the old study design  
the rest is in unit 3, so it might be on the exam

[akira88]

I was thinking of this exact same question, I came across them in some practise exam I did :O
Thanks for the clear up stonecold- but is what you wrote about cracking is all we need to know?

[stonecold]

I thought equilibrium may be something important in Unit 4.

Yeah, that is all you need to know about cracking.  We go into it in much more depth in Unit 4 I believe.

An example is like  Decane ----> Ethene + Octane

[naved_s9994]

You need to know this:

-Cracking (thermal or catalyctic) are reactions where alkanes are reacted to form an alkane and an alkene.
-Catalyst is an inorganic substance that increases the rate of reaction by lowering the activation energy required for the reaction.  Enzymes do the same thing, but are organic, highly specific, and will only function in a narrow range of conditions.
-Activation energy is the amount for energy required to begin a chemical reaction.

I don't really get what you mean by equilibrium.  I would just use that term to describe mole ratios.
'The reaction is complete when the reactants are in equilibrium, according to the mole ratio.'

Something like that.

You should also know what catalysts are to be used depending on the reaction.
i.e. Phosphoric acid for ethene ---> ethanol
     Sulfuric acid for alkanol + carboxilic acid ---> ester + water
     etc.

Well basically thats all you need to know.
The only thing for general knowledge, I'd add would be its USE. It's used in industry to
cost save, as by cracking, you use less energy/ hence money is saved. Otherwise without cracking there
would be a great deal of energy required, to form lighter fractions...hence more heat required--> costing more money

[Mao]

-Cracking (thermal or catalyctic) are reactions where alkanes are reacted to form an alkane and an alkene.

As well as a special case (dehydrogenation), where alkane --> alkene + H2

-Catalyst is an inorganic substance that increases the rate of reaction by lowering the activation energy required for the reaction.  Enzymes do the same thing, but are organic, highly specific, and will only function in a narrow range of conditions.

Enzymes only work under certain conditions, but these are often a few thousand times more effective than artificial catalysts. Also, most artificial catalysts are prone to being 'poisoned' (i.e. form complexes with reactants/intermediates) and degrade in their effectiveness over time. Most catalysts work by providing alternative pathways.

-Activation energy is the amount for energy required to begin a chemical reaction.

Think of a reaction as reactants --> break bonds --> intermediate --> form new bonds --> products. Thus, the energy required to break bonds must be added for the reaction to proceed. A catalyst decreases this energy by participating in the reaction, forming a different intermediate at lower energy, thus less energy is required to break bonds.

I don't really get what you mean by equilibrium.  I would just use that term to describe mole ratios.
'The reaction is complete when the reactants are in equilibrium, according to the mole ratio.'

Something like that.

I'm not quite sure what you mean, but equilibrium is in unit 4. I would avoid mentioning it in a unit 3 exam. Equilibrium is related to mole ratios, but in a different way. Equilibrium concentrations themselves don't actually have a direct relationship to the mole ratio. You will learn more about these in a few months.

[kenhung123]

Does inorganic have any difference in one being used up in reaction and the other is not?

[akira88]

Does inorganic have any difference in one being used up in reaction and the other is not?

All catalysts are not part of the products in a reaction, therefore they are not used up