MCQ ON THERMODYNAMICS

Gibb’s free enrgy is defined as [Pb. CET 2001] (a) (b) (c) (d) Standard enthalpy and standard entropy changes for the oxidation of ammonia at are and , respectively. Standard Gibbs energy change for the same reaction at is [CBSE PMT 2004] (a) – 439.3 kJ (b) – 523.2 (c) – 221.1 (d) – 339.3 For spontaneity of a cell, which is correct [Orissa JEE 2004] (a) (b) (c) (d) The free energy for a reaction having . at is [Orissa JEE 2005] (a) – 9336 cal (b) – 7386 cal (c) –1936 cal (d) + 9336 cal The and for a reaction at one atmospheric pressure are +30.558 kJ and respectively. The temperature at which the free energy change will be zero and below of this temperature the nature of reaction would be [Kerala CET 2005] (a) 483 K, spontaneous (b) 443 K, non-spontaneous (c) 443 K, spontaneous (d) 463 K, non-spontaneous (e)463 K, spontaneous. Adsorption of gases on solid surface is generally exothermic because [IIT JEE (Screening) 2004] (a) Enthalpy is positive (b) Entropy decreases (c) Entropy increases (d) Free energy increase Two mole of an ideal gas is expanded isothermally and reversibly from 1 litre ot 10 litre at . The enthalpy change (in ) for the process is [IIT JEE (Screening) 2004] (a) 11.4 kJ (b) –11.4 kJ (c) 0 kJ (d) 4.8 kJ Heat of neutralization of strong acid against strong base is constant and is equal to [EAMCET 1980; AFMC 1989; DPMT 1991; MP PET 1999; BHU 1999; MP PMT 1995] (a) 13.7 kcal (b) 57 kJ (c) J (d) All of the above The value of heat generated when 36.5 gm and 40 gm of reacts during neutralization [NCERT 1984; CPMT 1993] (a) 76.5 kcal (b) 13.7 kcal (c) More than 13.7 kcal (d) 108 kcal When a gas undergoes adiabatic expansion, it gets cooled due to [DCE 2002] (a) Loos of kinetic energy (b) Fall in temperature (c) Decrease in velocity (d) Energy used in doing work The heat content of a system is called (a) Internal energy (b) Entropy (c) Free energy (d) Enthalpy To calculate the amount of work done in joules during reversible isothermal expansion of an ideal gas, the volume must be expressed in [KCET (Med.) 2001] (a) only (b) only (c) only (d) Any one of them In an isobaric process, the ratio of heat supplied to the system and work done by the system for diatomic gas is [AFMC 2002] (a) 1 : 1 (b) 7 : 2 (c) 7 : 5 (d) 5 : 7 The enthalpy change for the reaction of 50.00 ml of ethylene with 50.00 ml of at 1.5 atm pressure is . The value of will be [DPMT 2004] (a) –0.3024 kJ (b) 0.3024 kJ (c) 2.567 kJ (d) –0.0076 kJ Enthalpy of solution of (solid) in water is . When is dissolved in water, the temperature of water [UPSEAT 2004] (a) Increase (b) Decreases (c) Does not change (d) Fluctuates indefinitely In which of the following entropy decreases ? [CPMT 1988, 94; MP PMT 2000] (a) Crystallization of sucrose from solution (b) Rusting of iron (c) Melting of ice (d) Vaporization of camphor For conversion C (graphite) ( C (diamond) the is [MP PMT 2001; MP PET 2003] (a) Zero (b) Positive (c) Negative (d) Unknown For a reaction and Which of the following statements is correct for the reaction [AMU (Engg.) 2000] (a) Reversible and Isothermal (b) Reversible and Exothermic (c) Spontaneous and Endothermic (d) Spontaneous and Exothermic For a reaction to occur spontaneously [CBSE PMT 1995] (a) must be negative (b) must be negative (c) must be negative (d) must be negative The total amount of energy in the universe is fixed, but [AMU (Engg.) 1999] (a) Disorder is increasing (b) Lightning is increasing (c) Matter is increasing (d) Gravitation is decreasing If for a given substance melting point is and freezing point is , then correct variation shown by graph between entropy change and temperature is [DCE 2001] (a) (b) (c) (d) In endothermic reaction, the value of change in enthalpy is [Pb. CET 2001] (a) Positive (b) Negative (c) Zero (d) None of these Which of the following would be expected to have the largest antropy per mole [MP PMT 2004] (a) (b) (c) (d) The enthalpies of formation of and are and respectively. for the reaction is [KCET 2003] (a) (b) (c) (d) Heat of reaction at constant volume is measured in the apparatus (a) Bomb calorimeter (b) Calorimeter (c) Pyknometer (d) Pyrometer Which of the following gas has the highest heat of combustion (a) Methane (b) Ethane (c) Ethylene (d) Acetylene The amount of heat measured for a reaction in a bomb calorimeter is [AIIMS 1991] (a) (b) (c) (d) For an endothermic reaction where represents the enthalpy of the reaction in kJ/mole, the minimum value for the energy of activation will be [IIT JEE 1992; MP PET 1993] (a) Less than (b) Zero (c) More than (d) Equal to The heat of neutralization of a strong acid by a strong base is nearly equal to [MP PET 1993; BCECE 2005] (a) + 57.32 J (b) – 57.32 kJ (c) + 13.7 J (d) – 13.7 kJ A Beckmann thermometer is used to measure [Kurukshetra CEE 2002] (a) High temperature (b) Low temperature (c) Normal temperature (d) All temperature The heat required to raise the temperature of a body by 1 K is called [AIEEE 2002] (a) Specific heat (b) Thermal capacity (c) Water equivalent (d) None of these Mechanical work is specially important in system that contain [Kerala (Med.) 2002] (a) Solid-liquid (b) Liquid-liquid (c) Solid-solid (d) Amalgam (e) Gases “The quantity of heat which must be supplied to decompose a compound into its element is equal to the heat evolved during the formation of that compound from the elements.” This statement is known as (a) Hess's law (b) Joule's law (c) Le–chatelier's principle (d) Lavoiser and Laplace law Hess law deals with [BHU 1979] (a) Changes in heat of reaction (b) Rate of reaction (c) Equilibrium constant (d) Influence of pressure on volume of a gas For which one of the following reactions, is not equal to [IIT JEE 1995] (a) ⇌ (b) ⇌ (c) ⇌ (d) ⇌ The heat liberated when 1.89 g of benzoic acid is burnt in a bomb calorimeter at increases the temperature of 18.94 kg of water by .If the specific heat of water at is 0.998 cal/g-deg, the value of the heat combustion of benzoic acid is [CPMT 1999; BHU 2000] (a) 771.1 kcal (b) 871.2 kcal (c) 881.1 kcal (d) 981.1 kcal For a hypothetic reaction , the activation energies for forward and backward reactions are 19 kJ/mole and 9 kJ/mole respectively. The heat of reaction is [CBSE PMT 2000] (a) 28 kJ (b) 19 kJ (c) 10 kJ (d) 9 kJ The enthalpy of neutralization of by is . The enthalpy of ionisation of will be [BHU 1997] (a) 4.519 kJ (b) 45.10 kJ (c) 451.9 kJ (d) 45.19 kJ In thermodynamics, a process is called reversible when [AIIMS 2001] (a) Surroundings and system change into each other (b) There is no boundary between system and surroundings (c) The surroundings are always in equilibrium with the system (d) The system changes into the surroundings spontaneously Which of the following unit represents largest amount of energy [AMU 2001] (a) Calorie (b) Joule (c) Erg (d) Electron volt Which of the following will have the highest bond energy [MP PMT 1990] (a) (b) (c) (d) therefore [DPMT 2001] (a) ; (b) (c) Graphite is the stabler allotrope (d) Diamond is harder than graphite Enthalpy of formation of two compounds x and y are – 84 kJ and – 156 kJ respectively. Which of the following statements is correct [CBSE PMT 2001] (a) x is more stable than y (b) x is less stable than y (c) Both x and y are unstable (d) x and y are endothermic compounds For the process dry ice [KCET 2000] (a) is positive while is negative (b) Both and are negative (c) Both and are positive (d) is negative while is positive For melting of 3 moles of water at the is [MP PMT 2001] (a) Zero (b) + ve (c) – ve (d) Unpredictable The equilibrium constant of a reaction at is and at is . What is the sign of for the reaction [Pb. CET 1998] (a) (b) is negative (c) is positive (d) None of these Which of the following has lowest fusion temperature [MP PET 2003] (a) Naphthalene (b) Diamond (c) NaCl (d) Mn Consider the reactions The bond energy of bond is [JIPMER 1997] (a) (b) (c) (d) Given the bond energies and bonds are and respectively, the enthalpy of the following reaction is [EAMCET 1992; JIPMER 1997] (a) (b) (c) (d) The relation between and for a cell is ; the cell reaction will be spontaneous if [MP PET 1995] (a) is negative (b) is positive (c) is negative (d) is positive 1. (a) (Gibb’s free energy equation) 2. (d) 3. (d) ; For spontaneity , 4. (a) 5. (d) or If sign mean. If is reversible process 6. (b) Due to randomness of particles is reduced since entropy decreases. 7. (c) The process is isothermal therefore ; 8. (d) . 9. (b) When strong acid and strong base neutralize each other than the value of heat generated is about 13.7 kcal. 10. (b) Due to fall in temperature. 11. (d) . 12. (d) As it involves the ratio , volume can be used in any units. (R should be in joules). 13. (b) ; ; {for diatomic of gas } 14. (a) ; , ; 15. (a) Since process is exothermic then heat is evolved due to this temperature of water increases. 16. (a) Because randomness is decreases. 17. (c) Conversion of graphite into diamond is an endothermic reaction. So, heat of diamond is higher than that of graphite. But would be negative for the conversion of graphite into diamond. 18. (c) and both are for spontaneous change, and for endothermic reaction. 19. (a) is negative for spontaneity. 20. (a) Entropy (a measure of disorder) of universe is increasing toward maximum. This is II law of thermodynamics. 21. (a) For a pure substance and represent the same temperature. Hence A is a correct choice. 22. (a) For endothermic reaction enthalpy of products > enthalpy of reactant Hence, change in enthalpy, Positive 23. (d) Suppose the no. of gm, 1gm for each case so the max. no of mole expected for which has to expected maximum entropy. 24. (b) …..(i) …..(ii) By (i) – (ii) . 25. (a) Bomb calorimeter is used to measure heat of reaction. 26. (b) Larger the number of C and H atoms, greater is the heat of combustion. 27. (c) The bomb calorimeter is used to measure . 28. (c) 29. (b) . 30. (b) Backmann thermometer is used to measure low temperature. 31. (b) Heat required to rise the temperature of a body by 1K called thermal capacity of the body. 32. (e) Mechanical work is important only in gases as they undergo appreciable change in volume. 33. (d) It is Lavoisier and Laplace law. This is another law of thermochemistry which was put forward before Hess's law. 34. (a) It is also known as "constant heat summation" law. It state that the total amount of heat evolved or absorbed in a reaction is same whether the reaction takes place in one step or in a number of steps. 35. (c) In this reaction so . 36. (a) = 37. (c) for forward reaction for backward reaction . 38. (d) 39. (c) Thermodynamics is a reversible process in which surroundings are always equilibrium with system. 40. (a) . 41. (b) Order of bond energy : 42. (c) Heat energy is also involved when one allotropic form of an element is converted in to another. graphite is the stabler allotrope because the heat of transformation of . (i) (ii) . 43. (b) The compound Y possess less energy than the X and thus Y is more stable than X. 44. (c) Both and are positive. 45. (a) For equilibrium . 46. (b) Equilibrium constant is decreases with temperature and is also decreases so it is –ve. 47. (a) The fusion temperature of napthalene is minimum, because it is non-polar covalent compound and has less fusion temperature. 48. (a) The bond energy of bond is y kcal . 49. (a) Net. energy released = 2346 – 2253 = 93 kJ i.e. ΔH = – 93 kJ . 50. (d) If than the cell reaction will be spontaneous. THERMODYNAMICS Mrs. SHALLU JINDAL AGGARWAL : (M)9878608983 Energy Enthalpy (H Ea Ea > (H TA TB (S T TA TB (S T TA TB (S T TA TB (S T