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Chapter 8 Chemical Equilibrium Chemistry 11th Class Punjab Short Questions

Question No. 1 - A catalyst does not affect the equilibrium position and Kc of a reversible reaction. Explain ?

Answer No. 1 - In most of the reversible reactions, the equilibrium is not always reached within a suitable short time. So an appropriate catalyst is added. A catalyst does not effect the equilibrium position of the reaction. It increases the rates of both forward and backward reactions and it reduces the time to attain the state of equilibrium. Actually a catalyst lowers the energy of activation of both forward and reverse steps by giving new path to the reaction.

Question No. 2 - State Le-Chatlier's principle?

Answer No. 2 - Le-Chatlier's principle:If stress is applied to a system at equilibrium, the system will act in such a way so as to nullify as for as possible the effect of that stress.

Question No. 3 - Reversible reaction attains the position of equilibrium which is dynamic in nature and not static.Explain it?

Answer No. 3 - At Equilibrium state the reaction is not stopped.Only the rate of forward reaction become equal to reverse reaction.Since reaction is in progress in both the direction. Therefore equilibrium is dynamic in nature not static.

Question No. 4 - Define Kr and Kb for reversible reactions?

Answer No. 4 - Kr and Kb: Kf is rate constant for forward reaction and Kb is rate constant for reverse or backward reaction. At equilibrium, rate of forward reaction becomes equal to reverse reaction.

Question No. 5 - Write two application of equilibrium constant?

Answer No. 5 - There are following applications of equilibrium constant.
Prediction of direction of reaction.
Extent of a chemical reaction.
Effect of various factors on chemical equilibrium.

Question No. 6 - Why the equilibrium constant value has its units for some of the reversible reactions but has not units for some other reactions?

Answer No. 6 - Units of Kc depends upon the number of moles of reactions and products involved in the reaction.

1. If number of moles of reactant and products are same it has no unit.

2. If number of moles of reactants are different from products then Kc has units, related to the concentration or pressure.

Question No. 7 - What will be nature of solution when (s) pH is more than 7 (b) pH is smaller than 7?

Answer No. 7 - pH scale generally ranges from 0 to 14. When pH is less than 7 the solution has acidic nature.When pH is greater than 7 then solution is base.

Question No. 8 - Why do rates of forward reactions slow down the reversible reaction approaches the equilibrium stage?

Answer No. 8 - The rate of forward reaction is directly proportional to molar conc. of reactants.Near the equilibrium stage, the concentration of reactant become small. Therefore the rate of forward reaction slow down due to decrease in concentration.

Question No. 9 - State Law of Mass Action?

Answer No. 9 - The rate at which substance reacts is directly proportional to its active mass and the rate of reaction is directly proportional to the product of active masses of the reactants.

Question No. 10 - Explain the terms buffer and buffer capacity?

Answer No. 10 - Buffer: The solution which resist the change in pH by the addition of small amount of an acid or base is called buffer.
Buffer Capacity: The capacity of a buffer to maintain definite pH is called buffer capacity.

Question No. 11 - Differentiate between acidic and basic buffers?

Answer No. 11 - The buffer which is prepared by mixing a weak acid and a salt of it with a strong base is known as acidic buffer. Such solutions give acidic buffers with pH less than 7. Mixture of acetic acid and sodium acetate is one of the best example of such a buffer.
The buffer which is prepared by mixing a weak base and a salt of it with a strong acid is known as basic buffer.Such solution give basic buffers with pH more than 7 mixture of NH4OH and NH4CI is one of the best example of basic buffer.

Question No. 12 - Define buffer solution.Give an example of basic buffer?

Answer No. 12 - Buffer Solution: The solution that resist in pH changes when small amount of an acid or base is added to it is called buffer solution.It is formed by mixing a weak base and its salt with strong acid.e.g NH4OH/NH4 CI

Question No. 13 - Why we need buffer solution?

Answer No. 13 - Buffers are the substances which resist the change in pH. Buffers are very important in many areas of chemistry.Buffers are needed in chemical analysis, pharmaceuticals, electroplating etc.

Question No. 14 - What will be nature of solution when: (a) pH=3.0 (b) pH=8.0?

Answer No. 14 - The value of pH varies between 0-14.A solution having pH value 0-7 are acidic in nature while a solution having pH value 7-14 are basic in nature.
1. PH= 3 This solution is acidic.
2. pH= 8 This solution is basic.

Question No. 15 - A mixture of NH4OH and NH4CI gives a basic buffer.Justify the statement ?

Answer No. 15 - A buffer which consists of a weak base and its salt with strong acid is called basic buffer.Since NH4OH is a weak base and NH4CI is its salt with strong acid.Therefore it is basic buffer.

Question No. 16 - Define state of Dynamic Equilibrium.

Answer No. 16 - When the forward and reverse reactions are taking place exactly at the same rate the equilibrium established is called dynamic equilibrium.

Question No. 17 - Define pH and pOH. Give its equation?

Answer No. 17 - pH:The negative logarithm of H+ Ions concentration is called pH.
pH = -LOG[H+ ]
pOH:The negative logarithm of OH- Ions concentration is called pOH.
pOH =-log [OH-]

Question No. 18 - What will be the nature of solution having pH equal to 12?

Answer No. 18 - The value of pH varies between 0-14.A solution having pH value 0-7 are acidic in nature while a solution having pH value 7-14 are basic in nature.
PH=12, This solution is basic.

Question No. 19 - Solubility of glucose increase in water by heating.Give reason?

Answer No. 19 - Formation of solution of glucose in H2 O is an endothermic process.The solution becomes cold.Therefore , according to Le-Chatelier's principle an increase in temperature will favour the formation of glucose solution.Thus by increasing temperature more quantity of glucose will dissolve in water.

Question No. 20 - How Kc predict the extent of chemical reaction?

Answer No. 20 - The value of Kc also helps us to predict extent of chemical reaction. There are three possibilities.

1. Large Kc Value: If Kc value is large it means reaction is almost completed.

2. Small Kc Value: If Kc value is small amount it means reaction does not proceed appreciably in forward direction. Small amount of product will be formed

3. Kc is in fractions: If Kc is in fractions. It means little forward reaction.

Question No. 21 - How can you determine Ksp From solubility?

Answer No. 21 - Solubility are given in number of grams of solute per 100g of H2O .Since density ofH2O is 1 gcm-3.Therefore solubility can be written as number of grams of solute/100 cm-3Of solvent. From the amount of solute/dm3Is calculated.Then amount in grams is converted into moles and using equilibrium KspCan be calculated.

Question No. 22 - Is it true that the sum of Pka and pKb is always equal to 14 at all temperature for any acid?

Answer No. 22 - It is not true because pKa and pKb values are temperature dependent. The degree of ionization of any acid increases as the temperature increases.Hence the value of Pka and pKb change with change in temperature.

Question No. 23 - What are Buffer Solutions? How Acidic Buffers are prepared?

Answer No. 23 - Those solution, which resist the change in their pH when a small amount of an acid or a base is added to them, are called buffer solutions.They have specific constant value of pH and their pH values do not change on dilution and on keeping for a long time.
Acidic buffer is prepared by mixing a weak acid and a salt of it with a strong base.Such solution give acidic buffers with pH less than 7.Mixture of acetic acid and sodium acetate is one of the best example of such a buffer.

Question No. 24 - The change of temperature disturbs both the equilibrium position and equilibrium constant of a reaction.Explain with reason?

Answer No. 24 - According to Le-Chatelier's principle an increase in temperature will favour the endothermic reaction and decrease in temperature will favour the exothermic reaction.Therefore change of temperature will disturb equilibrium position.The Equilibrium constant is temperature dependent therefore with the change of temperature a new equilibrium a position will be established.

Question No. 25 - What are application of buffer in daily life?

Answer No. 25 - Buffers are important in many areas of chemistry and allied science like molecular biology, microbiology, cell biology, soil science, nutrition and the clinical analysis.

Question No. 26 - Give the physical significance of Kf and Kb?

Answer No. 26 - The rate of forward and reverse reaction tell us the condition on which a reaction will depend. It also tells about:

1. Direction of area action

2. Extent of reaction.

Question No. 27 - Explain the term reversible reaction and state of equilibrium?

Answer No. 27 - State of Equilibrium: The state of reversible reaction in which rate of forward reaction becomes equal to rate of reverse reaction is called chemical equilibrium.There are two types:Static EquilibriumDynamic Equilibrium.

Question No. 28 - Write two uses of buffer solution?

Answer No. 28 - 1. The pH of human blood is maintain at 7.35 with the help of buffers. A higher or lower value than this may prove fatal.
2. Buffers are used in many industrial processes like electroplating, dyes etc.

Question No. 29 - What are buffer solutions? How a basis buffer can be prepared?

Answer No. 29 - The solution that resists in pH changes when small amount of an acid or a base is added to it is called buffer solution.
Basic buffers are formed by mixing a weak base and its salt with strong acid.Such solution will give basic buffers with pH more than 7.Mixing of NH4OH and NH4CI is one of the best example of such a basic buffer.

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