CBSE NCERT Solutions For Class 11 Chemistry Chapter 6

Class–XI–CBSE-ChemistryThermodynamicsCBSE NCERT Solutions for Class 11 Chemistry Chapter 6Back of Chapter Questions1. Choose the correct answer. A thermodynamic state function is a quantity(i) used to determine heat changes(ii) whose value is independent of path(iii) used to determine pressure-volume work(iv) whose value depends on temperature onlySolution:A thermodynamic state function is a quantity whose value is independent of a path. Functions likeetc. depend only on the state of a system and not on the path.2. For the process to occur under adiabatic conditions, the correct condition is:(i)(ii)(iii)(iv)Solution:A system is said to be under adiabatic conditions if there is no exchange of heat between thesystem and its surroundings. Hence, under adiabatic conditions,3. The enthalpies of all elements in their standard states are:(i) unity(ii) zero(iii)(iv) different for each element

The enthalpy of all elements in their standard state is taken to be zero.4.of combustion of methane isThe value ofis(i)(ii)(iii)(iv)Solution:givenSinceTherefore, alternativeandis correct.5. The enthalpy of combustion of methane, graphite and dihydrogen atare,andrespectively. Enthalpy of formationofwill be(i)(ii)(iii)(iv)Solution:According to the question,

ii)Thus, the desired equation is the one that represents the formation ofi.e.,Enthalpy of formation of6. A reaction,is found to have a positive entropy change. The reaction will be(i) possible at high temperature(ii) possible only at low temperature(iii) not possible at any temperature(v) possible at any temperatureSolution:Given :positivenegative (since heat is evolved)For a reaction to be spontaneous at constant pressure and temperature ,should be negative.According to the question, for the given reaction,negativeTherefore, the reaction is spontaneous at any temperature. Hence, alternativeis correct.

Class–XI–CBSE-ChemistryThermodynamics7. In a process,of heat is absorbed by a system andis the change in internal energy for the process?of work is done by the system. WhatSolution:Given: heat is absorbed by a system 701 Jwork is done by the system 394 JAccording to the first law of thermodynamics,Formula :change in internal energy for a process ((Since heat is absorbed than sign of q is positive )(Since work is done by the system so sign of w is negative )Substituting the values in a formulawe getHence, the change in internal energy for the given process is8. The reaction of cyanamide,andwas found to bereaction atwith dioxygen was carried out in a bomb calorimeter,atCalculate the enthalpy change for theSolution:Formula : Enthalpy change for a reactionWhere,change in internal energy change in the number of moles (moles of product – moles of reactant )For the given reaction,

sAnd,We know : Substituting the values in the expression of9. Calculate the number of of heat necessary to raise the temperature offromtoMolar heat capacity of isSolution:molar mass of aluminium 27From the expression of heatWhere,molar heat capacity mass of substance change in temperature () 20Moles of Al weight/molecular weight 60/27Substituting the values in the expression ofof aluminium

Class–XI–CBSE-ChemistryThermodynamics10. Calculate the enthalpy change on freezing ofatof water atto ice atSolution:Given :of water 1.0Total enthalpy change involved in the transformation is the sum of the following changes:(a) Energy change involved in the transformation ofwater atof water at(b) Energy change involved in the transformation ofof water at(c) Energy change involved in the transformation ofof ice attototoofof ice atof ice atHence, the enthalpy change involved in the transformation is11. Enthalpy of combustion of carbon toisformation ofoffrom carbon and dioxygen gas.Solution:Calculate the heat released upon

Class–XI–CBSE-ChemistryThermodynamicsGiven: Enthalpy of combustion of carbon to Weight ofFormation offrom carbon and dioxygen gas can be represented as:Heat released on formation ofThe heat released on formation of12. Enthalpies of formation ofrespectively. Find the value ofandarefor the reaction:andSolution:Given: Enthalpies of formation of Enthalpies of formation of for a reaction is defined as the difference betweenreactants.value of products andFor the given reaction,Substituting the values offorandfrom given data, we get:value of

Class–XI–CBSE-ChemistryHence, the value ofThermodynamicsfor the reaction is13. GivenWhat is the standard enthalpy of formation ofgas?Solution:Given :Standard enthalpy of formation of a compound is the change in enthalpy that takes place duringthe formation ofof a substance in its standard form from its constituent elements in theirstandard state.Re-writing the given equation forofStandard enthalpy of formation of14. Calculate the standard enthalpy of formation ofSolution:from the following data:

Class–XI–CBSE-ChemistryThermodynamicsThe reaction that takes place during the formation ofcan be written as: (i)(ii)(iii)(iv)The reaction (i) can be obtained from the given reactions by following the algebraic calculationsas:15. Calculate the enthalpy change for the processand calculate the bond enthalpy ofwhereinis enthalpy of atomizationSolution:The chemical equations implying to the given values of enthalpies are:(i)(ii)(iii)(iv)

Class–XI–CBSE-ChemistryThermodynamicsThe enthalpy change for the given processfollowing algebraic calculations as:can be calculated using theinso Bond enthalpy ofbond in16. For an isolated system,what will beSolution:Sincei.e. The Changes in internal energy ( U) for an isolated system is zero So; it does not exchangeany energy in any form with the surroundings.But , The entropy tends to increase in case,will be positive, i.e. greater than zeroof spontaneous reaction.17. For the reaction atandAt what temperature will the reaction become spontaneous, consideringover the temperature range?Solution:From the expression,Assuming the reaction at equilibrium,for the reaction would be:andto be constant

Class–XI–CBSE-ChemistryThermodynamicsFor the reaction to be spontaneous,must be negative. Hence, for the given reaction to bespontaneous, should be greater than18. For the reaction,what are the signs ofandSolution:The given reaction; the formation of chlorine molecule from chlorine atoms.Here, bond formation is taking place. Therefore, energy is being released. Hence,is negative.Also, two moles of atoms have more randomness than one mole of a molecule. Since spontaneityis decreased,is negative for the given reaction.19. For the reactionandCalculatefor the reaction, and predict whether the reaction may occur spontaneously.Solution:For the given reaction,

ituting the value ofin the expression of 12977.572 JSubstituting the values ofSinceandin the expression offor the reaction is positive so the reaction is non- spontaneously.20. The equilibrium constant for a reaction isSolution:At equilibrium 0 and Q Hancefor the reaction,What will be the value of

Class–XI–CBSE-ChemistryThermodynamics21. Comment on the thermodynamic stability ofgivenSolution:The positive value ofindicates that heat is absorbed during the formation ofThismeans thathas higher energy than the reactants ( and ). Hence,is unstable.The negative value ofindicates that heat is evolved during the formation ofandThe product,is stabilized with minimum energy.Hence, unstablefromchanges to unstable22. Calculate the entropy change in surroundings whenconditions.ofis formed under standardSolution:It is given thatof heat is evolved on the formation ofequal amount of heat will be absorbed by the surroundings.Entropy change of the surroundingsofThus, an

Class–XI–CBSE-Chemistry Thermodynamics CBSE NCERT Solutions for Class 11 Chemistry Chapter 6 Back of Chapter Questions 1. Choose the correct answer. A thermodynamic state function is a quantity (i) used to determine heat changes (ii) whose value is independent of path (iii) used to determine pressure-volume work