Chemical Forums
Chemistry Forums for Students => Analytical Chemistry Forum => Topic started by: AhmedEzatAlzawalaty on March 19, 2007, 02:53:02 PM
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the order of the reaction H2+I2=2HI is second order.The order of the raection H2+Br2=2HBr is 1.5
how the rate of the latter couldnt be like the rate of the former rections?
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The two reactions probably proceed through different reaction mechanisms.
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do you know what that mechanism is?
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Unfortunately, no. Sorry.
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Does any one know what the mechanism is?
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Dear ahmedezat,
Mr. Bodenstein found by his experiments, that the following Formula
for the Reactiontime holds for Br2:
d[HBr] / dt = [/sub] k’ * [H2] * [Br2]½
k’’ + [HBr] / [Br2]
YES, what surprise: [Br2]½ !!!
As the reaction is Light induced to build first radicals:
0.) Br2 <?> 2Br. (fast! )
Next Steps: A.) Br. + H2 ?> HBr + H. (slow!)
B.) H. + Br2 ?> HBr + Br. (fast! )
That’s telling you, that reaction A.) is relevant for the reaction speed,
and the whole "thing" is a so called "chain-reaction" ,
so in this case, (for H2 + Cl2 too, but NOT for H2 + I2!), it means,
you have to use:
d[HBr] / dt = k’ * [H2 ] * [Br.] from A.)
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From 0.) it follows, that: [Br.] = ? K * [Br2] , and combined:
d[HBr] / dt = k’ * K½ * [H2] * [Br2]½
Now, may be all clear?
Good Luck!
ARGOS++
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Thank u vey much, ARGOS++