Dekoyl's Questions

[chem-nerd]

catalysts LOWER the activation energy of a reaction (ie E' is lower than E'') thus there will be a higher proportion of particles with sufficient kinetic energy to react

[ilovevce]

Just a confirmation..
Is it true that catalysts affect the reaction by having more particles have lower kinetic energy and uncatalysed reactions have a lower number of particles at higher kinetic energy?
(Image removed from quote.)
That's one of the answers to Heinemann.

What that diagram shows is that a catalyst reduces the kinetic energy requirement for the reaction to proceed (i.e. it lowers the activation energy). The catalyst does not do anything to the kinetic energy of the actual particles.

In the diagram E' represents the activation energy with a catalyst. E'' represents the activation energy without a catalyst. E' is lower and so at any instant in time more particles will have the required energy to overcome the activation energy barrier. Hence, the reaction will happen faster.

[dekoyl]

^Thanks to both of you.

Q:How would you measure the rate of a reaction (more specifically between limestone and hydrochloric acid) in a school laboratory?

I'm just interested in people's answers if this were in an exam or something.
Thanks

[/0]

You could measure:
The pH of the solution.
The volume of evolved.
The mass of solution remaining after the has been expelled.

[TrueTears]

you could also measure the time taken by using the stop watch

[dekoyl]

You could measure:
The pH of the solution.
The volume of evolved.
The mass of solution remaining after the has been expelled.

Yeah you got it
Did you happen to come across this question before?

you could also measure the time taken by using the stop watch

Oh yeah. Thanks

[/0]

You could measure:
The pH of the solution.
The volume of evolved.
The mass of solution remaining after the has been expelled.

Yeah you got it
Did you happen to come across this question before?

you could also measure the time taken by using the stop watch

Oh yeah. Thanks

Yeah we spent half a period on the whole concept in class

[dekoyl]

I think this is a bit trivial but... Can catalysts change weight? I know that they aren't consumed in the reaction, so does it mean that the weight of the catalyst will not be effected at all?
Thanks

[TrueTears]

Change weight of the final products or the weight of the catalyst itself?

soz I can't interpret anything today

[dekoyl]

Change weight of the final products or the weight of the catalyst itself?

soz I can't interpret anything today

Change of the catalyst itself.

Sorry if I didn't make that clear

[TrueTears]

If the catalyst loses weight due to a reaction with a reagents, then it itself would be a reagent not a catalyst.

But if it speeds up the reaction first then loses some weight (maybe it might decompose or something), then yeah it's still a catalyst so I don't see why it can't lose any weight. As far as it fulfilled its role of speed up the reaction it can do whatever the hell it wants lolz.

[dekoyl]

^Thanks TT!

Q: Do the size of containers affect the rate of reaction? I know it will for reactions occurring in gaseous state but how about in solution?
Thanks!

[ilovevce]

^Thanks TT!

Q: Do the size of containers affect the rate of reaction? I know it will for reactions occurring in gaseous state but how about in solution?
Thanks!

First of all, I should clarify what is meant by rate of reaction. There are actually two different definitions that are commonly used.

1. The real rate of reaction is simply a measure of how many moles of a reactant are converted per unit time. So if you simply have a greater bulk of reactants then your rate of reaction will be greater. The unit would be mol/s. This is not useful for understanding how quickly a certain percentage of reactants will be converted.

2. The definition that is perhaps more useful is 'rate of reaction per unit volume'. This tells us the rate at which reactants are converted for each unit of volume. The unit would be or . I will call this the 'specific rate of reaction' and it is useful for giving us an idea of how quickly a certain percentage of the original amount of reactants will actually be converted.

If we are talking about specific rate of reaction, then the size of the container will have no effect upon this value. However, if you are adding one reactant to another, the size and shape of the container will affect the speed and manner in which the two reactants mix. So that things aren't too complicated, always assume that when one reactant is added to another the two mix perfectly. If this is the case, size will not affect the specific rate of reaction.

I hope that all makes sense.

[ilovevce]

I think this is a bit trivial but... Can catalysts change weight? I know that they aren't consumed in the reaction, so does it mean that the weight of the catalyst will not be effected at all?
Thanks

Applying the principle of conservation of mass, if a catalyst loses mass, then that means some of the catalyst has reacted, and the products have been carried away. But we know that catalysts do NOT react. So no, catalysts do not lose mass.

In reality, catalyst surfaces do wear down over time, and need to be replaced every so often. This is not actually  because the catalyst reacts - rather, the catalyst gets worn down and particles of the catalyst get carried away (like how rocks slowly erode over time).

[dekoyl]

There's a question that's been bugging me...
I've got here in my notes that the pH of water decreases when it is heated. I don't fully understand why this is so.
Thanks to anyone who can explain it better than my teacher =P