Energetics Questions and Answers

16 The heat evolved during the combustion of 112 litre of water gas at STP mixture of equal volume of H and CO is Given H g 1 2O g H O g AH 241 8 kJ CO g 1 2O g CO g AH 283 kJ 1 241 8 kJ 3 1312 kJ 2 283 kJ 4 1586 kJ 12

129 The heat of neutralization of HCI by NaOH is 135 55 9 kJ mol If the heat of neutralization of HCN by NaOH is 12 1 kJ mol The energy of dissociation of HCN is 1 43 8 kJ 2 68 11 2 43 8 kJ

3 Numerically equal to the heat of formation 4 1 and 3 both TC0135 120 The value of AH for the combustion of C s is 127 94 4 kCal The heat of formation of CO g is 1 49 5 kCal 2 94 4 kCal 3 188 0 kCal 4 More data required TC0136

252 Pre Medical Chemistry 115 The combustion of one mole of benzene takes place 121 at 298 K and 1 atm After combustion CO g and H O l are produced and 3267 0 kJ of heat is liberated Calculate the standard enthalpy of formation A H of benzene Standard enthalpies of formation of CO g and H O l are 393 5 kJ mol and 285 83 kJ mol respectively 1 48 51 kJ mol 2 48 51 kJ mol 122

95 For the reactions i H g Cl g 2HCl g xkJ ii H g Cl g 2HCI ykd Which one of the following statement is correct 1 x y 3 x y 2 x y 4 More data required TC0106

14 The enthalpy of formation for CH g CO g and H O at 25 C and 1 atm pressure are 52 394 and 286 kJ mole respectively The enthalpy of combustion of C H will be 1 1412 kJ mole 2 1412 kJ mole 3 142 2 kJ mole

94 The enthalpy of a reaction at 273 K is 3 57 kJ what will be the enthalpy of reaction at 373 K if 2 Zero AC zero 1 3 57 kJ 3 3 57 x 373 273 kJ 4 375 kJ 100 TH rea 1 3

18 be of 112 Heat of combustion of CH C H C H and C H gases are 212 8 373 0 337 0 and 310 5 kCal respectively at the same temperature The best fuel among these gases is 1 CH 2 C H 3 C H 112 Hea 4 C H TC0125 113 Given standard enthalpy of formation of

AIPMT 2015 8 The activation energy of a reaction can be determined from the slope of which of the following graphs 2 In k v s In k 1 TV S T T 1

22 If C H O s 90 g 6CO g 6H O g AH 680 kCal The weight of CO g produced when 170 kCal of heat is evolved in the combustion of glucose is 1 265 g 3 11 g 2 66 g 4 64 g

7 The heat of combustion of CH4C and H at 25 C are 212 4 K Cal 94 0 K Cal and 68 4 K Cal respectively the heat of formation of CH will be a 1 54 4 K Cal 3 375 2 K Cal 2 18 4 K Cal 4 212 8 K Cal TC0120 1 3 114 T H ar

5 The temperature at which the reaction Ag O s 2Ag s 1 0 g is at equilibrium is Given and 1 462 12 K 3 262 12 K AH 30 5 kJ mol AS 0 066 kJK mol 2 362 12 K 4 562 12 K TR007

Pre Medical Chemistry 251 CH and 109 The standard heats of formation of NO g and The AH N O g are 8 0 and 2 0 kCal mol respectively the heat of dimerization of NO in kCal is

and ozone 97 Reaction H s L g 2HI AH 12 40 kCal 1 According to this heat of formation of HI will be nd oxygen TC0101 1 12 40 kCal 3 6 20 kCal 2 12 40 kCal 4 6 20 kCal TC0108

1 55 2 kCal 3 55 2 kCal 2 30 2 kCal 4 19 4 kCal TC0114 103 The standard molar heat of formation of ethane CO and water are respectively 21 1 94 1 and 68 3 kCal The standard molar heat of combustion of ethane will be 2 162 kcal 4 183 5 kCal 1 372 kCal 3 240 kCal TC0115 1 110 ME 2 Wh OXU 1 3

8 For hypothetical reversible reaction 1 A g B g AB g AH 20 kJ if standard entropies of A B and AB are 60 40 and 50 JK mole respectively The above reaction will be in equilibrium at 1 400K 3 250K 2 500K 4 200K

104 The AH for CO CO and H O are 393 5 2 g 110 5 and 241 8 kJ mol respectively the standard enthalpy change in kJ for the reaction CO H CO H O is 2 1 524 1 2 41 2 3 262 5 4 41 2

105 The enthalpies of combustion of carbon and carbon monoxide are 393 5 kJ and 283 kJ respectively the enthalpy of formation of carbon monoxide is 1 676 5 kJ 3 110 5 kJ 2 110 5 kJ 4 676 5 kJ

119 H TC0125 113 Given standard enthalpy of formation of CO 110 kJ mol and CO 394 kJ mol The heat of combustion when one mole of graphite burns is 1 110 kJ 3 394 kJ 2 284 kJ 4 504 kJ CO136

of these The rate constant of first order reaction becomes 6 times when the temperature is increased from 350 K to 410 K Energy of activation for the reactin is 1 35 63 KJ mol 3 25 20 KJ mol 2 45 63 KJ mol 1 4 23 62 KJ mol

30 Which of the following reaction is expected never to be spontaneous 1 20 g 30 g AH Ve AS Ve 2 Mg s H g MgH AH Ve AS Ve 3 Br 1 Br g AH Ve AS Ve 4 2Ag s 3N g 2AgN AH Ve AS Ve 500

Determine the entropy change for the below 2H g Og 2H O at 300 K If standard entropies of H a Oa and H O 0 are 126 6 201 20 and 68 0J K mol respectively 1 218 4 JK mol 2 318 4 JK mol 1 3 520 2 J K mol 1 128 6 JK mol 201

When enthalpy and entropy change for a chemical reaction are 2 5 x 103 cal and 7 4 cal deg respectively predict the reaction at 298 K is 1 Spontaneous 2 Nonspontaneous 3 At equilibrium 4 None of these If a gas at constant temperature and pressure

53 The enthalpy of vaporisation of per mole of ethanol B pt 79 5 C and A S 109 8 JK mol is 1 27 35 kJ mol 2 32 19 kJ mol 4 42 37 kJ mol 3 38 70 kJ mol TD0058

250 Pre Medical Chemistry 90 Which of the following represents an exothermic reaction 1 N g O g 2NO g AH 180 5 kJ 2 H O g C s CO g H g AE 131 2kJ 3 2HqO s 180 4 KJ 2Hg O g

2 One mole of a gas occupying 3dm expands against a constant external pressure of 1 atm to a volume of 13 lit Find work is 1 10 atm dm 3 3 39 atm dm 2 20 atm dm 4 48 atm dm

reaction at 373 K if Zero 375 kJ TC0105 100 The enthalpy of formation of ammonia is 46 0 kJ mol The enthalpy change for the reaction 2NH g N g 3H g is 1 46 0 kJ mol 2 92 0 kJ mol 3 23 0 kJ mol 4 92 0 kJ mol TC0112 15 THERMODYNAMICS02 EXP

A chemist fills a reaction vessel with 6 53 atm nitrogen N gas 7 33 atm hydrogen H gas and 0 962 atm ammonia NH3 gas at a temperature 25 0 C Under these conditions calculate the reaction free energy AG for the following chemical reaction N g 3H g 2NH g 2 Use the thermodynamic information in the ALEKS Data tab Round your answer to the nearest kilojoule kJ

CH C C H C AH 270 6 KJ mol AS 139 0 J K mol Find value of AG at T 300 K 1 328 9 KJ mol 3 129 8 KJ mol 1 2 228 9 KJ me 4 528 9 KJ mc

1 2 6 1 Gibb s energy change for the dissolution of potassiumnitrate in water at 298 K is KNO S water K aq NO3 aq AH 34 KJ mol 45 0 116 KJ K mol 1 0 568 KJ mol 2 0 568 KJ mol 3 1 036 KJ mol

WORK DONE IN DIFFERENT PROCESS 40 The work in ergs for a reversible expansion of one mole of an ideal gas from a volume of litres to 20 litres at 25 C is 10 1 2 303 x8 314 x 10 x298 log2 2 2 303 x0 0821 x 298 log2 3 2 303 x0 0821x298 log 0 5 4 2 303 x2x298 log2 TH0043

57 For the reaction A s B s C g the value of AH 30 56 kJ mol and AS 66 JK mol The temperature at which the free energy change for the reaction will be zero is 1 373 K 3 463 K 2 413 K 4 493 K

9 According to the following reaction C s 1 2O g CO g AH 26 4 kCal 1 CO is an endothermic compound 2 CO is an exothermic compound 3 The reaction is endothermic 4 None of the above

1 A BC D AH 10 000 J mol AS 33 3 J mol K At what temperature the reaction will occur spontaneous from left to right 1 300 3 K 2 300 3 K 3 300 3 K 4 None of these

7 A first order reaction is 50 completed in 2 minutes at 27 C and 5 minutes at 47 C The ener of activation of the reaction is 1 43 85 KJ 3 11 97 KJ 2 55 14 KJ 4 6 65 KJ

3 890 KJ 4 3570 10 moles of an ideal gas expand isothermally and reversibly from a pressure of 5 atm to latm at 300 K what is work done 1 40 15 x 10 J 2 20 30 10 J 3 18 x 10 J 4 55 x10 J Enthaly of formation of H O is 68 Kcal mole 13 126 6 201 20 and 1 218 4 JK ma 2 318 4 J K ma 3 520 2 J K ma 4 128 6 JK me Out of E H q War 1 E H W

5 A swimmer coming out from a pool is covered with a film of water weighing about 80g How much heat must be suplied to evaporte this water Aap H 40 79 KJ mol 1 181 KJ 2 362 KJ 3 90 5 KJ 4 40 79 KJ

Enthaly of formation of H O is 68 Kcal Enthalpy of formation of OH ions Given 4H H 0 13 7 Kcal mol 54 3 Kcal mol 2 57 3 Kcal ma 4 20 1 Kcal ma

The ratio of the difference in energy between the first and second Bohr orbit of H to that between the second and the third Bohr orbit is 1 1 2 2 1 3 3 4 9 4 27 5

1 AH AE 3 AH AE 2 AH AE 4 None TH0037 35 For which change AHAE 1 H g g 2HI g 2 HCI 0 NaOH NaCl s H O 0 3 C s O g CO g 4 N g 3H g 2NH g Sessio TH0038

CK0033 33 The hypothetical reaction A B 2AB follows the mechanism as given below 34 A A A fast A B AB B slow A BAB fast The order of the over all reaction is 1 2 2 1 3 1 The rate for the reaction 4 Zero CK0034 ZE 40

mol 4 16 g of methane was subjected to combus C in a bomb calorimeter system The teme the calorimeter system including water was rise by 0 5 C Heat of combustion of me constant pressure is Heat capacity lorimeter system is 17 7 KJ K 890 KJ 890 KJ 2 885 KJ 4 885 KJ e standard beats of formation of CH fol

ant on C 30 Heat of reaction for CO g 1 2O g CO g at constant V is 67 71 K cal at 17 C The heat of reaction at constant P at 17 C is 1 68 0 kCal 3 67 42 kCal 2 68 0 kCal 4 None TH0032

38 For which of the following reactions AH is less than AE 1 C H O s 60 g 6CO g 6H O 0 2 2SO g O g 2SO g 3 N O g 2NO g ONC

4 At room temperature 300 K orange juice gets spoilt in about 52 hours In a referigerator at 200 K ju can be stored three times as long before it gets spoilt Estimate a the activation energy of the reaction that causes the spoiling of juice mistry Ex b How long should it take for juice to get spoilt at 400 K Given In 3 1 1 e 11 20 1 733

TH0029 8 For the reversible isothermal expansion of one mole of an ideal gas at 300 K from a volume of 10 dm to 20 dm AH is 1 1 73 kJ 2 1 73 kJ 3 3 46 kJ 4 Zero

2 The difference between heats of reaction at constan pressure and constant volume for the reaction 2CH 150 g 12CO g 6H O at 25 C in KJ is 1 7 43 3 7 43 2 3 72 4 3 72 TH0024

CK0014 5 For the reaction H g Br g 2HBrg the experimental data suggests Rate The order for this reaction is K H Br 1 2 2 3 1 4 22

134 Given CO H 10 20 2 200 CO HO AH 393 5 kJ mol AH 285 8 kJ mol CO 2H O CH 20 en AH 890 3 kJ mol Based on the above thermochemical equations the value of AH at 298 K for the reaction C 2H CH will be 1 144 0 kJ mol 2 74 8 kJ mol 3 144 0 kJ mol 4 74 8 kJ mol 4 Co H O JCI Q 134 far COCO AH H 0 H O CO 2H O after 298 K H 393 5 kJ mol 1 144 0 kJ mol 3 144 0 kJ mol 285 8 kJ mol 20 AH 890 3 kJ mol a C2H g CH g 2 74 8 kJ mol 4 74 8 kJ mol

When a certain amount of titanium is placed in a bomb calorimeter that has a heat capacity of 10 00 kJ K the temperature increases from 25 00 to 70 00 C If the heat of combustion of titanium is 1 98 x 10 kJ mol how many grams of titanium were added to the calorimeter