Energetics Questions and Answers

Consider the following reaction Calculate AG for this reaction at 25 C under these conditions CO g CCl4 g 2COC1 g Pco Pccl PCOCI AG for CO g is 394 4 kJ mol AG for CC14 g is 62 3 kJ mol and AG for COC1 g is 204 9 kJ mol Express the energy change in kilojoules per mole to one decimal place 0 130 atm 0 175 atm 0 755 atm

The enthalpy of vaporisation of liquid is Q 7 30 kJ mol and entropy of vapourisation is 75 J mol K The boiling point of the liquid at 1 atm is 1 250 K 3 450 K 2 400 K 4 600 K 1 250 K 3 450 K t 30 kJ mol 75 J mol K 1 atm 2 400 K 4 600 K

JEE ADVANCED A S for the reaction A2 g B2 g AB2 g A S 298 K 17 J k mol at 5 bar and 298 K is 2 A 23 69 JK mol B 23 69 JK mol C 10 31 JK mol 10 31 JK mol mperature 0 K

26 Standard enthalpy of vapourisation AH Q 26 for water a 100 C is 40 66 kJmol The internal energy of vaporisation of water at 100 C in kJmol is 1 43 76 3 37 56 2 40 66 4 43 76 100 C ofert pretent ApH 40 66 Tituls Gift 1 43 76 3 37 56 kJmol 1 100 C 2 40 66 4 43 76 kJmol

The dissolution of CaCl2 6H O in large volume of water is endothermic to the extent of 3 5 kcal mol For the reaction CaCl s 6H O l CaCl 6H O s AH 23 2 kcal Hence heat of solution of CaCl2 anhydrous in a large volume of water is

ectrolytes of solute ALLEN 26 At a certain temperature pure water has H O 1067 mol L What is the value of Kat this temperature

ET CHEMISTRY 16 The Gibb s energy for the decomposition of Q 16 Al O3 at 500 C is as follows All India Major Test Series Phase I II Major Test 45 39 10 09 2020 500 C TR Al O fac fad fr Afafea sid ALO Al 0 A G 960 kJ mol The potential difference needed for the electrolytic reduction of aluminium oxide Al O3 at 500 C is at least 1 2 5 V 3 4 5 V 2 5 0 V 4 3 0 V ALO AI O AG 960 kJ mol 500 C 1 2 5 V 3 4 5 V AL O faga 782 f fand side 2 5 0 V 4 3 0 V

Based on the given information AG Cao 604 2 kJ mol and AG Al2O3 1582 kJ mol which of the following is correct a 3CaO 2Al Al2O3 3Ca is spontaneous b 3CaO 2AI Al2O3 3Ca is non spontaneous c AG for the reaction 3 CaO 2AI Al2O3 3Ca is 230 6 d AG for the reaction 3CaO 2AI Al2O3 3Ca is 977 8

5 A hydrogen gas electrode is made by dipping Q 15 platinum wire in a solution of HCl of pH 10 and by passing hydrogen gas around the platinum wire at one atm pressure The oxidation potential of electrode would be 1 1 18 V 2 0 059 V 3 0 59 V 4 0 118 V was is BI54RG310 pH lex a 1 1 18 V 3 0 59 V 1 atm Sex and A 2 0 059 V 4 0 118 V

The enthalpy of combustion of methane graphite and dihydrogen at 298 are 890 3 kJ mol 393 5 kJ mol and 285 8 kJ mol respectively Enthalp of formation of CH g will be 74 8 kJ mol iii 74 8 kJ mol ii iv 52 27 kJ mol 52 26 kJ mol

Predict the signs of AH AS and AG for the evaporation of water at 25 C For each give an explanation Also describe the temperature dependence of AG H O l H O g The sign of AH is The sign of AS is The sign of AG is The reaction is spontaneous at because because because temperatures

We can regard table salt NaCl is a relatively simple material When we compress it the atoms directly push against each other causing the bonds between atoms to become shorter The bond energy U between Na and Cl atoms in NaCl is about 5 x 10 19 J The distance between atoms is about 0 282 nanometers 1 nm 1x 10 9 m 1 Use this information to estimate the elastic modulus of NaCl Give your answer in GPa i e giga Pascals

variation a hollow Pre Medical Physics 207 40 The gravitational potential energy is maximum at 1 infinity 2 the earth s surface 3 The centre of the earth

11 Following curve shows the variation of intensity of gravitational field I with distance from the centre of solid sphere r 1 2 3 Ft R R Session GRO011

259 An ideal gas heat engine operates in carnot cycle between 227 C and 127 C It absorbs 6 x 10 cal of heat at higher temperature Then amount of heat converted to work is 1 2 4 x 10 cal 3 1 2 x 10 cal 2 6 x 10 cal 4 4 8 x 10 cal HT0280

DA T0278 on taking to 50 HT0280 260 A refrigerator works between temperature 10 C and 27 C the coefficient of performance is 2 1 4 15 47 X 21 1 7 1 3 8 1 HT0285

256 A camot engine shows efficiency of 40 on taking energy at 500 K To increase the efficiency to 50 at what temperature it should take energy 1 400 K 2 700 K 3 600 K 4 800 K HT0279

atic ve er 59 242 The volume of a poly atomic gas 3 1 compressed adiabatically to of the original volume If the original pressure of the gas is P the new pressure will be 1 8 Po 3 6 P on 2 16 Po 4 2 P HT0265 PHYSICS EXEROSEP65

HT0258 236 Graphs between P V diagram for isothermal and adiabatic processes are drawn the relation between their slopes will be 1 Slope of adiabatic curve y slope of isothermal curve 2 Slope of isothermal curvey slope of adiabatic 3 Slope of isothermal curve slope of adiabaticSIO 4 Slope of adiabatic curve y slope of isother

s expended and a simillar is expanded ALLEN 238 One mole ideal gas is compressed adiabatically at 27 C Its temperature becomes 102 C The work done in this process will be y 1 5 1 625 J 2 625 J

HT0272 SECOND LAW OF THE HEAT ENGINES AND REFRIGERATORS THERMODYNMAMICS 20 250 According to the second law of thermodynamics 1 heat energy cannot be completely converted to work 2 work cannot be completely converted to heat energy 3 for all cyclic processes we have dQ T 0 4 the reason all heat engine efficiencies are less than 100 is friction which is unavoidable

235 If an ideal gas is compressed during isothermal process then 1 No work is done against gas 2 heat is rejected by gas 3 It s internal energy will increase 4 Pressure does not change 24

0265 the 243 During isothermal isobaric and adiabatic processes work done for same change in volume will be maximum for P 1 Isothermal 2 Isobaric 3 Adiabatic B

230 When a gas is adiabatically compressed then it s temperature increase because 1 Work done is zero 2 Internal energy is increased 3 Heat is supplied to it 4 No change in pressure 202

4 89 g of a gas 21 2 g mol was dissolved in liquid water in a calorimeter with a calorimeter constant of 75 7 J K 1 Prior to mixing everything was equilibrated to 86 4 C The resulting solution with a mass of 33 6 g was observed to be at a temperature of 101 7 C and have a specific heat capacity of 3 89 Jg K 1 Determine q per mole for this dissolution process a 8670 J mol b 1 37 x 104 J mol c 1 77 x 105 J mol d 3160 J mol e 1 37 x 104 J mol

essed to ht about adiabatic crease in Pre Medical Physics 95 228 One mole of an ideal monoatomic gas is heated at a constant pressure of one atmosphere from 0 C to 100 C Then the change in the internal energy is 1 20 80 x 10 J 2 12 48 x 10 J

ease in 229 The specific heat of a gas at constant pressure is more than that of the same gas at constant volume because 1 Work is done in the expansion of gas at constant re will 0245 which s given Q 0246 pressure 2 Work is done in the expansion of the gas at contant volume 3 The molecular attraction incrcase under constant pressure 4 The vibration of molecules increases under constant pressure

HT0255 233 A quantity of air y 1 4 at 27 C is compressed suddenly the temperature of the air system will 1 Fall 2 Rise 3 Remain unchanged

215 P V plots for two gases during adiabatic processes are shown in the figure Plots 1 and 2 should correspond respectively to PA 1 He and O 3 He and Ar Session 2 O and He 4 O and N HT0237

1 The neutron lifetime for a neutron produced by fission in a thermal reactor is 10 3 sec For a reactivity of 0 05 determine the power increase of a reacto in 2 seconds State any assumptions reference any data table or plot used

d It is less rea One mole of an ideal gas is allowed to expand reversibly and adiabatically from a temperature of 27 C If the work done during the process is 3 kJ then final temperature of the gas is C 20 J K V a 100K b 150K c 195K d 195 K d 255 K

Two equal and like charges when placed 5 cm apart experience a repulsive force of 0 144 newtons The magnitude of the charge in micro coulomb will be 1 0 2 2 2 3 20 4 12

HT0226 206 If the heat of 110 J is added to a gaseous system and change in internal energy is 40 J then the 2 amount of external work done is 1 180 J 2 70 J HOD 3 110 J 4 30 J HT0227

2 Two rigid adiabatic vessels A and B which initially contains two gases at different temperatures are 5 connected by pipe line with valve of negligible volume The vessel A contains 2 moles Ne gas C P m 2 p m at 300 K vessel B contains 3 moles of SO2 gas Cp is 4 and 6 litre respectively The final total pressure in atm when valve is opened and 12 Kcal heat supplied through it to vessels Use R 2 cal mol K and R 0 08 L atm mol K as per desire B A Ne 11 R 1 4 R at 400 K The volume of A B vessel SO

con Effect of temperature gros the solubility of a solid in a liquid is significantly affected by temper changes Consider the equilibrium represented by equation 2 112 being dynamic equilibrium must follow Le Chateliers Princip general if in a nearly saturated solution the dissolution pro endothermic Asol H 0 the solubility should increase with temperature and if it is exothermic sol H 0 the solubility decrease These trends are also observed experimentally Effect of pressure IN Pressure does not have any significant effect on solubility of s liquids it is so because solids and liqu compr Ten mi 5

207 If amount of heat supplied is Q work done is W and change in internal energy is mC dT then relation among them is C gram specific heat 1 mC dT Q W 2 Q W mC dT 4 None of these 3 Q mC dT W 0339

HT0203 187 For a diatomic gas change in internal energy for unit change in temperature at constant pressure and volume is U and U respectively then U U is 1 5 3 4 5 7 2 7 5 3 1 1

178 On mixing 1 g mole of a monoatomic with 1 g mole of a diatomic gas the specific heat of mixture at constant volume will be 1 R 2 3 2 R 3 2R 4 5 2R HT0194 BOBO BATARGET PHYENG MC

2 37 The heat of hydrogenation of benzene is 51 kcal mol and its resonance energy is 36 kcal mol What will be the heat of hydrogenation of cyclohexene 1 18 kcal mol 3 50 kcal mol 2 29 kcal mol 4 26 kcal mol

4 Two moles of ethanol C H5OH are subjected to isothermal compression from 10 atm to 20 atm at 40 C Calculate the change in free energy in kJ mol for this liquid compression The mass density of ethanol 0 789 g ml 18 pts

A mass of diatomic gas Y 1 4 at a pressure of 2 atm is compressed adiabatically so that its temperature rise from 27 C to 927 C The pressure of the gas is final state is 1 28 atm 2 68 7 atm 3 256 atm 9 otm

261 Which of the following is correct for fre expansion of ideal gas under isotherma condition 1 q 0 AT 0 w 0 2 q 0 AT 0 w 0 3 q 0 AT 0 w 0 4 q 0 AT 0 w 0

10 72 Pre Medical Physics 89 162 If the root mean square speed of hydrogen molecules is equal to root mean square speed of oxygen molecules at 47 C the temperature of hydrogen is 1 20 K 2 47 K

vo components D Formation of a solution can be considered as 1 pure solvent separated solvent molecules AH pure solute separated solute molecules AH ii iii separated solvent and solute molecules solution AH Solution so formed will be ideal if a AH soln AH AH AH3 b AH soln AH AH AH3 c AH soln AH3 AH AH d AHsoln AH AH AH3

swered Answers Molar enthalpy of fusion of ice is 6 008 kJ mol at 273 15 K and 1 bar Molar volum of fusion is 1 6 cm mol What will be the melting point in K of ice at 100 bar 265 8 Between 272 2 and 272 6 O with margin 0 0 with margin 0

143 A body is thrown with a velocity of 9 8 m s making an angle of 30 with the horizontal It will hit the ground after a time 1 3 s 2 2 s 3 1 5 s 4 1s

anu find b of He 24ml mol Molecular diameter of He is 2 67 10 For a hypothetical gas a 4 0 atm L mol of then Te of gas is loovigonelyg C fons x 0 Tc 27Rb 2 da 33 33 9c for Yangur pressure Viscosity Surface tension 8x4 27x

3 Two spheres P and Q of same colour having radii 8 cm and 2 cm are maintained at temperatures 127 C and 527 C respectively The ratio of energy radiated by P and Q is 1 0 054 3 1 2 0 0034 4 2

86 If a piece of metal is heated to temperature 0 and 90 then allowed to cool in a room which is at temperature 0 the graph between the temperature T of the metal and time t will be closest to T 1 0 3 T4 2 0 4 TA 91

1 The standard heat of formation of sodium ions in aqueous solution from the following data will be Heat of solution NaOH aq from NaOH s 470 7 kJ Heat of formation of OH aq from OH s 228 8 kJ a 251 9 kJ c 241 9 kJ For the rag b 241 9 kJ d 251 9 kJ