Does volume affect the reaction rate?

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Does volume affect the reaction rate?

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Answer 1 · 2018-06-22T10:07:05

Does volume affect concentration?

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

$r (t) = k {[A]}^{m} {[B]}^{n}$ $r(t) = k[A]^m[B]^n$

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

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

$Conc. = \frac{Number of particles}{unit volume}$ $"Conc." = "Number of particles"/"unit volume"$

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.

$\frac{Number of particles constant}{↑ unit volume} \Rightarrow Conc. ⏐ ⏐ ⏐ ⏐ ↓$ $"Number of particles constant"/(uarr "unit volume") => "Conc." darr$

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,

$\frac{↑ Number of particles}{↑ unit volume} \Rightarrow Conc. stays constant$ $(uarr "Number of particles")/(uarr "unit volume") => "Conc. stays constant"$

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Does volume affect the reaction rate?

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