- #1
adf89812
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- TL;DR
- When to Multiply by Constants and do exponentiation in rate law equation ?
When to use exponents or multiply by constants in the rate law?
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Discussion Overview
The discussion revolves around the application of stoichiometric coefficients in rate laws, particularly when to use exponents versus multiplying by constants. Participants explore the implications of stoichiometry on reaction rates and concentration terms, with a focus on single-step kinetics and the internal structure of molecules.
Discussion Character
- Technical explanation
- Debate/contested
- Mathematical reasoning
Main Points Raised
- Some participants propose that concentration should be raised to the power of the stoichiometric coefficient, suggesting that the internal structure of the molecule does not affect this rule in single-step kinetics.
- Others question the origin of the doubling effect in reaction rates when stoichiometric coefficients are applied, particularly in relation to how reactants are consumed.
- There is a suggestion that the stoichiometric coefficient can influence both the rate and the exponent on the concentration term, but this is debated.
- Some participants argue that it is possible to perform calculations without doubling the rate, although they acknowledge that the stoichiometric coefficient must be considered at some point.
- A hypothetical scenario involving homonuclear triatomic molecules is raised, questioning whether the corresponding concentration should be cubed while the rate remains unaffected unless specified by stoichiometry.
- One participant emphasizes that the internal structure of the molecule is irrelevant to the discussion of stoichiometric coefficients.
Areas of Agreement / Disagreement
Participants express differing views on the implications of stoichiometric coefficients on reaction rates and concentration terms. There is no consensus on whether the stoichiometric coefficient always leads to a doubling of the rate or if it can be applied in different ways depending on the context.
Contextual Notes
Some assumptions about the relationship between stoichiometry and reaction rates remain unresolved, particularly regarding the effects of molecular structure and specific scenarios involving different types of molecules.
- #2
Borek
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You raise concentration to the power given by the stoichiometric coefficient, internal structure of the molecule (amount of atoms of different elements) doesn't matter (well, it can matter for the mechanism, but for a single step kinetics these are just black boxes doing some magic).
This is not different from the way reaction quotient is defined.
This is not different from the way reaction quotient is defined.
- #3
adf89812
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where does the doubling in theBorek said:
- #4
Borek
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Rate of the reaction is ##k_3[H_2][ I]^2## but because of the stoichiometry I is consumed twice as fast.
- #5
adf89812
- 37
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The stoichiometry coefficient of two means both double the speed and square the exponent on the concentration term always?Borek said:
- #6
adf89812
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the stoichiometry coefficient on the reactant side of the decomposition has two effects always?adf89812 said:
- #7
Borek
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Many ways to skin that cat. In general it is perfectly possible to do the calculations without doubling the rate, but this stoichiometry coefficient needs to be used at some point.
- #8
adf89812
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If there were homonuclear triatomic molecules, would that mean cubed the corresponding concentration but don't multiple the rate by three unless the stoichiometry means it's concentration is three times that of the others?Borek said:
- #9
Borek
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adf89812 said:
Why? I already told you whatever is inside the molecule doesn't matter.
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