Simple Diffusion Misconception

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lhh2003
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I get smaller molecules diffuse faster than larger ones across the membrane due to them passing more easily through gaps between phospholipids.

But in conditions WITHOUT membranes, would larger molecules / ions undergo simple diffusion faster than smaller ones due to them colliding and separating at a faster rate ?
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Thiexp53
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Under conditions without membranes larger molecules would still diffuse slower than smaller ones because lighter molecules can move faster under the same temperatures (their internal kinetic energy is the same). Using the equation Ke = 1/2mv2 we can see that if the kinetic energy is the same but there is a larger mass then the velocity of the particles must decrease in order to have a constant kinetic energy, this means larger molecules move slower and so diffuse slower.
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