# How Does the Rate Law Indicate Reaction Mechanism Complexity?

In summary, the conversation discusses the rate law for a chemical reaction and whether it occurs through a single-step mechanism. The rate law formula is given and it is determined that the experimentally determined rate law does not match the expected expression, indicating that the reaction is not a single-step mechanism.
"The Rate Law" in Chemistry

Hey I've just been working on a chemistry lab lately in my chemistry course, and one of the problems on the lab write-up asks to:

Write the rate law for the following reaction, if it were to occur through a single-step mechanism.
2I^-(aq) + S2O8^2-(aq) -> 2SO4^2-(aq) + I2(aq)

Now since it is asking to write it as a single-step mechanism I would assume there is only one step needed.

Now in the lab it has given us this formula:

rate = -(delta[S2O8^-2])/(delta t) = -(1/2)(delta [I^-])/(delta t) = (1/2)(delta[SO4^2-])/(delta t) = (delta[I2])/(delta t)

So could you not just say the only step needed is:
-(delta[S2O8^-2])/(delta t) = (delta[I2])/(delta t)

Then for the second part to the question it asks "By examination of the experimentally determined rate law, explain whether this reaction does in fact proceed through a single-step mechanism. Explain."

Any help on this problem would be great, thanks.

The rate law would be

rate=k(forward)[I-]^2[S2O8]

does your experimentally determined rate law concur with this expression?

The rate law would be

rate=k(forward)[I-]^2[S2O8]

does your experimentally determined rate law concur with this expression?

Ahh I see what you are saying, yeah it's just
rate=k[S2O8^2-][I^-]^2

And my rate law does not coincide with this, therefore it cannot be a single-step mechanism. Gotcha! Thanks.

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## What is the rate law in chemistry?

The rate law in chemistry is a mathematical expression that describes the relationship between the reaction rate and the concentrations of reactants in a chemical reaction. It is also known as the rate equation or the rate expression.

## What is the purpose of the rate law?

The rate law helps us understand how the rate of a chemical reaction is affected by changes in the concentration of reactants. It also allows us to predict the rate of a reaction under different conditions.

## How is the rate law determined?

The rate law is determined experimentally by measuring the initial reaction rates at different concentrations of reactants. The data is then analyzed to determine the relationship between the rate and the concentrations of reactants.

## What is the difference between the rate law and the equilibrium constant?

The rate law describes the rate of a reaction while the equilibrium constant describes the ratio of product and reactant concentrations at equilibrium. The rate law is dependent on the concentrations of reactants while the equilibrium constant is not affected by changes in concentration.

## Can the rate law change?

Yes, the rate law can change under different conditions such as temperature, pressure, and the presence of a catalyst. These changes can affect the rate constant and the reaction mechanism, resulting in a different rate law.

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