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(i) What is the effect of added inert gason the reaction at equilibrium. (ii) Explain the equilibrium constants for heterogenous equilibrium. |
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Answer» SOLUTION :(i) When an inert gas (i.e., a gas which does not react with any other species involved in equilibrium) is added to an equilibrium system at constannt volume, the total number of moles of gases present in the container increases, that is, the total pressure of gases increases, the partial pressure of the reactants and the products are unchanged. Hence at constant volume, addition of inert gas has no effect on equilibrium. (ii) Equilibrium constants for heterogeneous equilibrium: Consider the following heterogeneous equilibrium. `CaCO_(3)(s) hArrCaO(s)+CO_(2)(g)` The equilibrium constant for the above reaction can be written as `K_(c)=([CaO(s)][CO_(2)(g)])/(CaCO_(3)(s))` A pure solid always has the same concentration at a given temperature, as it does not expand to fill its container. IE.., it has same number of moles `L-1` of its volume. therefore, the concentration of a pure solid is a constant. the above expression can be MODIFIED as follows `K_(c)=[CO_(2)(g)]` (or) `K_(p)=p_(CO_(2))` The equilibrium constant for the above reaction depends only the concentration of carbon dioxide and not the calcium carbonate or calcium oxide. similarly, the ACTIVE mass (concentration) of the pure liquid does not change at a given temperature. consequently, the concentration terms of pure liquids can also be excluded from the expression of the equilibrium constant. For example, `CO_(2)(g)+H_(2)O(l)hArr H^(+)(AQ)+HCO_(3)^(-)(aq)`. Since, `H_(2)O(l)` is a pure liquid the `K_(c)` can be expressed as `K_(c)=([H^(+)(aq)][HCO_(3)^(-)(aq)])/([CO_(2)(g)])`. |
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