Chp9_QuantElectr

# Chp9_QuantElectr - produce a certain amount of H 2 In other...

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Quantitative Electrochemistry The key to most of these problems is the link between the amount of charge, Q (not to be confused with the reaction quotient here), carried between an external circuit and the internal redox reaction. The working equation is: × = × = n t i Q where, i is the current in amps (A); t is the time in seconds; n is the number of mols of electrons; and is the Faraday constant. P. Example 9.12 For how long (s) must a 2.56A current be run to produce 25 mL of H 2 gas from water at 1.0 atm and at 298K. Step 1: Identify the appropriate, in this case, half-reaction: - - + + 1 2 1 2 2 ) ( 2 2 OH g H e O H KEY: Realize that we are effectively relating mols of electrons to mols of H 2 since the external current information relates quantitatively to mols electrons and we seek to
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Unformatted text preview: produce a certain amount of H 2 . In other words, as emphasized in chapter 1 & 2, a balanced reaction tells us relative proportion of mols! Step 2: Convert H 2 info to mols: ( 29 ( 29 ( 29 2 3 10 02 . 1 298 0821 . ) 025 . ( 00 . 1 H mol K L atm RT PV n-× = × × = = n.b. the appropriate value of the gas constant and that THIS ‘n’ is mol H 2 . Step 3: Use the balance reaction stoichiometry to convert mols of H 2 to mols of electrons:-× =-× ×--e mol H mol e mol H mol 3 2 2 3 10 04 . 2 1 2 10 02 . 1 Step 4: Now we exploit the “working equation” (where ‘n’ refers to electrons): min 28 . 1 . 77 56 . 2 485 , 96 10 04 . 2 3 = = × × = ℑ =-s A i n t...
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