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Author Topic: Temperature dependence of Gaseous diffusion and effusion  (Read 414 times)

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Viktor2

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Temperature dependence of Gaseous diffusion and effusion
« on: September 11, 2017, 11:01:53 AM »

As per the expression of rate of effusion, it is proportional to pressure but at the same time inversely proportional to square root of temperature. Can we say that as a combination, it will be directly proportional to square root of temperature?
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mjc123

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Re: Temperature dependence of Gaseous diffusion and effusion
« Reply #1 on: September 11, 2017, 10:56:04 PM »

No, because temperature and pressure can be separately varied.
Consider the gas equation P = nRT/V. Under what conditions will the rate of effusion be proportional to sqrt(T)?
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Viktor2

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Re: Temperature dependence of Gaseous diffusion and effusion
« Reply #2 on: September 12, 2017, 09:15:57 AM »

You want to say that changing temperature may not affect pressure, I think that for the constant volume it does, the expression of rate of diffusion has proportionality of P/sqrt(T) ... Can you explain that what can we say about effect of temperature on rate of effusion or diffusion?
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mjc123

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Re: Temperature dependence of Gaseous diffusion and effusion
« Reply #3 on: September 12, 2017, 10:49:36 PM »

If you're talking about a fixed amount of gas in a constant volume, then yes, pressure is proportional to temperature. Note that the condition for this is that n/V is constant, not simply V. If you just added more gas to the volume, so that you doubled the pressure without changing the temperature, the rate of effusion would change though T doesn't.
But I was talking (as I assumed you were) about the general case, where P, V and T are not specified. In that case you can't simply say effusion is proportional to sqrt(T); you have to state the dependences on P and T explicitly.
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