The ka of phosphoric acid, h3po4, is 7.6  10-3 at 25 °c. for the reaction h3po4 (aq) h2po4 - (aq) + h + (aq) ∆h° = - 14.2 kj/mol. what is the ka of h3po4 at 60 °c?

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Chemistry

Lennon

23 July, 18:21

The ka of phosphoric acid, h3po4, is 7.6  10-3 at 25 °c. for the reaction h3po4 (aq) h2po4 - (aq) + h + (aq) ∆h° = - 14.2 kj/mol. what is the ka of h3po4 at 60 °c?

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Neil Gilmore · Answer 1

Use the van't Hoff equation: ln (K2 K1) = Î" HÂş R (1 T1 â’ 1 T2) ln (K2 7.6*10^-3) = - 14,200 J 8.314 (1 298 â’ 1 333) ln (K2 7.6*10^-3) = â’ 1708 (0.00035) ln (K2 0.0076) = â’ 0.598 Apply log rule a = log b b a - 0.598 = ln (e â’ 0.598) = ln (1 e 0.598) Multiply both sides with e^0.598 K 2 e 0.598 = 0.0076 K e 0.598 e 0.598 = 0.0076 e 0.598 K 2 = 0.0076 e 0.598 = 4.2 â‹ ... 10 â’ 3 K2 = 4.2 â‹ ... 10 â’ 3