Q47 of 54 Page 94

Note: In the following questions a statement of Assertion (A) followed by a statement of Reason (R) is given. Choose the correct option out of the choices given below each question.

Assertion (A): For any chemical reaction at a particular temperature, the Equilibrium constant is fixed and is a characteristic property.


Reason (R) : Equilibrium constant is independent of temperature.


For any chemical reaction, Equilibrium constant is dependent on temperature. Any reaction will always have the same value of Equilibrium constant if the temperature at which reaction is carried out is kept same.


Therefore, Equilibrium constant at constant temperature is a characteristic property of a reaction i.e. it will always be same if temperature is same.


Equilibrium constant is not independent of temperature.


For e.g. consider an endothermic reaction. The reactant will require heat in order to proceed in forward direction and form products. So, if the temperature is increased, reactants will get heat to carry out reaction and more product will be formed at higher temperature. Thus, Equilibrium constant (which is basically the ratio of concentration of product upon that of reactant) will increase.


Therefore, we can say for endothermic reaction, increased temperature will be favoured and more product will be formed which in turn will increase value of K.


And for exothermic reaction, reverse is true.


So from this it can be said that K is dependent on temperature.

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45

Note: In the following questions a statement of Assertion (A) followed by a statement of Reason (R) is given. Choose the correct option out of the choices given below each question.

Assertion (A) : A solution containing a mixture of acetic acid and sodium acetate maintains a constant value of pH on addition of small amounts of acid or alkali.


Reason (R) : A solution containing a mixture of acetic acid and sodium acetate acts as a buffer solution around pH 4.75.


46

Note: In the following questions a statement of Assertion (A) followed by a statement of Reason (R) is given. Choose the correct option out of the choices given below each question.

Assertion (A): The ionisation of hydrogen sulphide in water is low in the presence of hydrochloric acid.


Reason (R) : Hydrogen sulphide is a weak acid.


48

Note: In the following questions a statement of Assertion (A) followed by a statement of Reason (R) is given. Choose the correct option out of the choices given below each question.

Assertion (A) : Aqueous solution of ammonium carbonate is basic.


Reason (R) : Acidic/basic nature of a salt solution of a salt of weak acid and weak base depends on Ka and Kb value of the acid and the base forming it.


49

Note: In the following questions a statement of Assertion (A) followed by a statement of Reason (R) is given. Choose the correct option out of the choices given below each question.

Assertion (A): An aqueous solution of ammonium acetate can act as a buffer.


Reason (R) : Acetic acid is a weak acid and NH4OH is a weak base.