Question

Does volume affect the reaction rate?

Answer 1

Does volume affect concentration?

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If you answered yes to that, then it affects reaction rate, as you see in every rate law...

`r(t) = k[A]^m[B]^n`

for reactants `A` and `B` of reactant orders `m` and `n` respectively, with their rate constant `k` at a given temperature `T` over time `t` for rate `r(t)`.

...and is not concentration the amount of substance divided by the volume?

`"Conc." = "Number of particles"/"unit volume"`

CASE I

• As container volume increases without adding more gas, reaction rates of gas-phase reactions decrease, as these gases will collide less frequently in a larger space.

`"Number of particles constant"/(uarr "unit volume") => "Conc." darr`

CASE II

• As the gas sample volume increases (e.g. as we add more gas into a flexible container, like a balloon), reaction rate stays about the same... The concentration effectively does not change due to the increase in mols of gas changing proportionally with the increase in container volume...

That is,

`(uarr "Number of particles")/(uarr "unit volume") => "Conc. stays constant"`

What is the distinction between the two scenarios?