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Explain effect of temperature change on chemical equilibrium by example. |
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Answer» Solution :When a change in TEMPERATURE of equilibrium reaction occurs the value of equilibrium constant `K_c` is changed. In general the temperature dependence of the equilibrium constant depends on the sing of `DeltaH` for the reaction. The RATE of reaction is also changed due to the changes of temperature. Exothermic reaction: The equilibrium constant for an exothermic reaction (negative `DeltaH`) decreases as the temperature increases : REVERSE reaction occurs, `Q_c` increases, products decrease. e.g. Production of ammonia is exothermic reaction. `N_(2(g)) + 3H_(2(g)) hArr 2NH_(3(g)) , DeltaH =-92.38 "kJ mol"^(-1)` According to Le-Chatelier.s principle, RAISING the temperature shifts the equilibrium to left and decreases the equilibrium concentration of ammonia. In other WORDS, low temperature is favourable for high yield of ammonia, but practically very low temperatures slow down the reaction and thus a catalyst is used. Endothermic reaction : The equilibrium constant for an endothermic reaction (positive `DeltaH`) increases as the temperature increases. Forward reaction will be occurs, `Q_c` decreases and products increases that types of equilibrium established. e.g, following reaction is endothermic. `{:("Reaction:",[Co(H_2O)_6]_((aq))^(2+)+,4Cl_((aq))^(-) hArr, 6H_2O_((l))+,[CoCl_4]_((aq))^(2-)),("Colour :","Pink","Colourless","Colourless","Blue"):}` At room temperature, the equilibrium mixture is blue due to `[CoCl_4]^(2-)` . When cooledin a freezing mixture, the colour of the mixture turns pink due to `[Co(H_2O)_6]^(3+)` |
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