Question

For which of the following reaction, $ {{K}_{p}} $ is equal to $ {{K}_{c}}? $

• A. $ PC{{l}_{5}}(g)\rightleftharpoons PC{{l}_{3}}(g)+C{{l}_{2}}(g) $
• B. $ 2S{{O}_{2}}(g)+{{O}_{2}}(g)\rightleftharpoons 2S{{O}_{3}}(g) $
• C. $ {{N}_{2}}{{O}_{4}}(g)\rightleftharpoons 2N{{O}_{2}}(g) $
• D. $ {{H}_{2}}(g)+{{I}_{2}}(g)\rightleftharpoons 2HI(g) $

Answer 1

Answer: (D)

$ {{K}_{p}}={{K}_{c}}{{(RT)}^{\Delta {{n}_{g}}}} $ where, $ \Delta {{n}_{g}}= $ number of moles of gaseous products-number of moles of gaseous reactants. Hence, for $ {{K}_{p}} $ to be equal to $ {{K}_{c}}, $ $ \Delta {{n}_{g}} $ should be zero. For the reaction, $ {{H}_{2}}(g)+{{I}_{2}}(g)\rightleftharpoons 2\,HI(g) $ $ \Delta {{n}_{g}}=2-2=0 $ Hence, $ {{K}_{p}}={{K}_{c}}\,.\,\,{{(RT)}^{0}}={{K}_{c}} $