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# Order of a Reaction Watch

1. Mg(s) + 2HCl (aq) --> MgCl2 (aq) + H2(g)

In the equation above, I can work out the order of HCl by adding magnesium ribbon to HCl, then collect the H2 gas and record the volume of gas at set time intervals. Plotting volume against time, I can find out the rate of reaction. Then if I repeat the experiment for different concentrations of HCl I can compare the rates of reactions and work out the order of HCl.

But how would I work out the order of magnesium / How do I change the concentration of magnesium?

(this is for the A2 Investigation Coursework)
2. (Original post by SherlockHolmes)
Mg(s) + 2HCl (aq) --> MgCl2 (aq) + H2(g)

In the equation above, I can work out the order of HCl by adding magnesium ribbon to HCl, then collect the H2 gas and record the volume of gas at set time intervals. Plotting volume against time, I can find out the rate of reaction. Then if I repeat the experiment for different concentrations of HCl I can compare the rates of reactions and work out the order of HCl.

But how would I work out the order of magnesium / How do I change the concentration of magnesium?

(this is for the A2 Investigation Coursework)
The rate equation tells you the relationship between rate and the concentrations of the species present.

Mg is a solid and hence cannot have a concentration.

The 'orders' only apply to dissolved substances or gases, i.e. something which is in a homogeneous phase.
3. (Original post by charco)
The rate equation tells you the relationship between rate and the concentrations of the species present.

Mg is a solid and hence cannot have a concentration.

The 'orders' only apply to dissolved substances or gases, i.e. something which is in a homogeneous phase.
I have been told to form a rate equation for the reaction, so is there anyway to modify the experiment or use a different equation to work out the orders of both the reactants?

If I dissolve magnesium powder in water first would this work?
4. (Original post by SherlockHolmes)
I have been told to form a rate equation for the reaction, so is there anyway to modify the experiment or use a different equation to work out the orders of both the reactants?

If I dissolve magnesium powder in water first would this work?
It is not possible to dissolve magnesium in water.

5. (Original post by charco)
It is not possible to dissolve magnesium in water.

I see... if magnesium cannot have a concentration then does that mean a rate equation does not exist for the reaction?
6. Mg doesn't 'really' have an order as it's solid afaik.
7. (Original post by tamimi)
Mg doesn't 'really' have an order as it's solid afaik.
Ok, now I am confused as to how I am meant to form a rate equation.

Thanks for the clarification anyway.
8. Its easier if you employ another reaction which involved 2 dissolved reactants, such as an acid-alkali neutralisation reaction. My teacher said so.

I think you should do for an organic reaction, shouldn't you? There are a lot of possible reactions

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9. (Original post by SherlockHolmes)
I see... if magnesium cannot have a concentration then does that mean a rate equation does not exist for the reaction?
Yes, you can have a rate equation, but it can only contain the acid concentration....
10. If anyone needs help check out retro teach 32 on tutor hunt
11. Thanks for the help everyone

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Updated: August 18, 2013
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