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I am a year 11 student studying high school chemistry and we are currently studying catalysts.

I am working on an assessment and need to come up with a unique but testable hypothesis surrounding one of the 5 variables of chemical reaction rate.

The 5 variables that affect the rate of a chemical reaction that my teacher have given to the class are as follows:

  • The concentration of each reactant (pressure of gases)
  • The temperature
  • The surface area of reacting solids
  • The nature of catalytic material
  • The quantity of catalytic material

So far I have come up with one testable question that I think is unique but need some help from others who will most definitely be more knowledgable than me.

My current question is, “Does the physical condition of a catalyst change its effect on a chemical reaction rate?”

To make this make any sort of sense, I intend on comparing the effect a powdered solid has as a catalyst, compared to a chunk of something, for example - zinc crushed into a powder, if that’s possible, versus a solid chunk of zinc of the same mass in the reaction between zinc and sulphuric acid.

If anyone knows any other good questions that are unique, or if my question seems worthy of putting into a hypothesis, I would greatly appreciate any input. Thanks in advance to anyone who reads all of this and helps me, you are a legend!

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The greater the surface area, the more accessible the reagent in a heterogeneous reaction. Hence, assuming the same chemical purity, Zn (metal) is less reactive than Zn (shot), and this is less reactive as Zn (dust) e.g. in the course of a Barbier reaction (e.g., THF/aqueous $\ce{NH4Cl}$, Zn, allyl bromide and carbonyl compound; it carries some similarities to the Grignard reaction). It equally «works» the less obvious way, i.e. old turnings of Mg (exposed for long to air) frequently have to be etched by a little of iodine to get past the oxidative layer to initiate the wanted Grignard reaction; finer shot is more prone to this, than coarse fresh turnings.

Though not used as a catalyst but as suspended reagent at lab scale, the efficiency of $\ce{MnO2}$ to oxidize organic compounds (e.g., allyl alcohols to the corresponding aldehydes and ketones) equally depends greatly from how this powder is synthesized in first place.* Polymorphism (different spatial arrangement of molecules in the solid/crystalline state; you possibly know about the allotropes of sulfur) and different frequency of defects in the solid state's structure seem to contribute to this observation. (The $\ce{MnO2}$ in dry cell batteries often is mangese dioxide prepared chemical synthesis (CMD), or electrolysis (EMD); this sum formula then can be a great simplification of the true composition.)

* See e.g. an earlier post here.

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Careful using the word unique. The 5 conditions put too much emphasis on catalysts. It is basically 3 conditions: Concentrations, temperature, and adequate mixing. A catalyst changes the mechanism. The new mechanism responds to the same three conditions; there is just an additional component to consider: the catalyst amount and its molecular size ie. concentration. Mixing is next. There are two main methods, stirring or shaking and flow over a surface.

If you want a simple system to consider try electrolysis of water. a simple equation involving two reactions with all the components. There is probably a kit in the school lab to set up an experiment, set up a cell in series with a battery, ammeter and light bulb. Current flow is the reaction rate; measure it by the ammmeter or a digital camera or Crookes radiometer to measure light intensity.

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My current question is, “Does the physical condition of a catalyst change its effect on a chemical reaction rate?”

That is a good question.

To make this make any sort of sense, I intend on comparing the effect a powdered solid has as a catalyst, compared to a chunk of something, for example - zinc crushed into a powder, if that’s possible, versus a solid chunk of zinc of the same mass in the reaction between zinc and sulphuric acid.

If this is your question, you might want to ask "How does the surface area of a catalyst affect reaction rate". It is a common question, but becomes unique as you choose the reaction to study, and the specific set of experiments to test it.

Unfortunately, in the reaction you suggest, the zinc is a reactant, not a catalyst. However, you could take a different reaction, and test how the rate of reaction changes when you switch from a chunk of catalyst to a powder.

I am working on an assessment and need to come up with a unique but testable hypothesis surrounding one of the 5 variables of chemical reaction rate.

At the high school level, it is hard to come up with a unique but testable hypothesis. On the one hand, it makes sense to propose to work on a reaction that is well-studied (for safety reasons), on the other hand, that makes it less unique. Maybe "unique" in this assignment just means you thought about it carefully rather than taking an experiment from the internet (like getting a complete answer here).

If anyone knows any other good questions that are unique, or if my question seems worthy of putting into a hypothesis, I would greatly appreciate any input.

Your question is worthy. You just have to find a good reaction to test it on.

You could research the catalytic decomposition of aqueous hydrogen peroxide catalyzed by manganese oxide. It is a well-known reaction, and it is easy to observe the reaction because one product is elemental oxygen that bubbles out of the reaction vessel. You would have to think about how to make your question a bit different from the questions you encounter in your research.

For academic honesty's sake, it would be appropriate to cite all the resources you used to formulate your hypothesis. This is exactly how scientific progress works, researching and citing prior work that is relevant to your own work.

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