Energetics Questions and Answers

If the solubility of cholesterol in methanol were 1 g 96 mL at 20 C and 1 g 4 2 mL at 80 C what is the absolute minimum amount of methanol needed to recrystallize 5 01 g cholesterol Report the number of mL to the nearest whole number OGMU 2020

If atmospheric pressure suddenly changes from 1 00 atm to 0 899 atm at 298 K how much oxygen will be released from 4 80 L of water in an unsealed container please put answer in scientific notation amount mol

Calculate the work done during combustion of 0 138 kg of ethanol C H5OH 1 at 300 K Given R 8 314JK mol molar mass of ethanol 46gmol A B 7482 J 7482 J Correct Answer

tion is false but reason is true Assertion Increasing pressure of pure water decreases its freezing point Density of water is maximum at 273 K Reason AIIMS 2003 a If both assertion and reason are true and the reason is the correct explanation of the assertion b If both assertion and reason are true but reason is not the correct explanation of the assertion c If assertion is true but reason is false d If the assertion and reason both are false e If assertion is false but reason is true

The difference in free energy of the reaction when all the reactants and products are in STP 1 atm and 298K is AG and ke and kp are the thermodynamics equilibrium constants of the reaction The relation between them is as follows 4 5 AG 2 303 RT log Kc and AG 2 303RT log Kp in case of ideal gas Which of the following statement is correct for a reversible process in state of equilibrium A AG 2 303 RT log K B AG 2 303 RT log K C AG 2 303 RT log K D AG 2 303 RT log K At 490 C the value of equilibrium constant k is 45 9 the reaction H g 1 g 2HI g Calculate the value of AG for the reaction at that temperature A 3 5 kcal B 3 5 kcal C 5 79 kcal D 5 79 kcal

The combustion of fuel in a piston cylinder causes an internal energy change of 2 843E3 kJ The components surrounding the cylinder absorb 9 566E2 kJ of heat How much work can be done by the fuel on the piston in the cylinder

Atmospheric O is measured in Dobson units 1 unit 2 69 x 1016 molecules O above each squared centimeter of Earth s surface Dobson thickness in hundredths of a millimeter that the O column would occupy if it were compressed to I atm at 0 C The graph shows variations in ozone concentration as a function of latitude and season Using an absorption cross section of 2 5 x 10 19 cm calculate the transmittance in the winter and the summer at 30 50 N latitude at which 0 varies from 290 to 350 Dobson units Twinter Tsummer Total ozone Dobson units 380 350 320 290 260 230 1989 1990 1991 30 N 50 N 10 N 30 N 10 N 10 S By what percentage is the ultraviolet transmittance greater in winter than in summer 1992 1993 Year Harris Lucy Quantitative Chemical Analysis 10e 2020 W H Freeman and Company Variation in atmospheric ozone at different latitudes Data from P S Zurer Chem Eng News 24 May 1993 p 8

The absorption cross section on the ordinate of the ozone absorption spectrum is defined by Transmittance T e b where n is the number of absorbing molecules per cubic centimeter is the absorption cross section in square centimeters cm and b is the panthlength in centimeters cm The total ozone in the atmosphere is approximately 8 x 10 8 molecules above each square centimeter of Earth s surface from the surface up to the top of the atmosphere If this were compressed into a pathlength of a 1 cm thick layer the concentration would be 8 x 10 8 molecules cm Ultraviolet radiation in the 200 to 280 nm range is essentially completely blocked by ozone in the atmosphere but barely absorbed in the 315 to 400 nm range Using the ozone spectrum estima the transmittance T and absorbance A of this 1 cm sample at 280 and at 340 nm Question 11 of 15 T at 280 nm A at 280 nm T740 Absorption cross section 10 19 cm 100 0 60 0 60 0 x 1000 250 CIO H CO 300 Wavelength nm Harris Lucy Quantitative Chemical Analysis 10e 2020 W H Freeman and Company 350 Spectra of trace gases in the atmosphere At ozone s maximum absorption at a wavelength near 260 nm a layer of ozone is more opaque than a layer of gold of the same mass Data from U Platt and J Stutz Differential Absorption Spectroscopy Berlin Heidelberg Springer Verlag 2008

AC Oce o 25801234 transienl interactions D CELL N cell D cell ACp Doe Noot 9540 1200 J mol K Using the above figure can you calculate the equlibrium constant between extracellula racellular folded protein N Denatured protein is designated D in the figure You ma inciples to calculate the value

21 Which of the following equations represents a AH f equation a CO2 g H2 g HCOOH HCOOH b CO g H O 1 C 2 C s 2 H2 g 2O2 g 2 HCOOH d C s H O 1 2O2 g HCOOH 1 C s H2 g O2 g HCOOH 1 e

Calculate the heat of formation of napthalene from the following data CO g L C S O g ii H g 1 2 O g iii C pHg S 120 g H O 1 10CO g GH O 1 H 94 405 Kcal H 68 3 Kcal H 94 405 Kcal

Select incorrect statement s A Entropy of an isolated system always remains constant during phase transition proces B AS 0 for reversible condensation of vapour surrounding C 4 G 0 for Br g at high temperature 2AB g 200 kJ D A g B g information AH AR a is 100 kJ mole

How much heat is evolved upon the complete oxidation of 6 g of aluminum at 25 C and 1 at 2Al2O3 s pressure for Al2O3 is 1676 kJ mol 4Al s 30 g Oa 85 59 kJ b 171 1 kJ Oc 342 3 kJ O d 9 238 x 10 kJ Oe 684 7 kJ

Question 2 a Under what conditions is a dA 0 condition that defines the spontaneity of a process b A sample containing 2 50 moles of He 1 bar 350 K is mixed with 1 75 mol of Ne 1 bar 350 K and 1 50 mol of Ar 1 bar 350 K Calculate AGmixing and ASmixing

ne voltage E of the cell Ag s AglO s Agt x M HIO3 0 300M Zn 0 4M Zn s f Ksp E 3 10 8 for AglO3 s and K 0 15 for HIO3 Ag Ag 0 8 V E Given 2 303RT F A 1 17 V C 3 02V Zn Zn 0 06 0 76 V B 2 17 V D 1 43

Question 1 a An ideal gas undergoes an adiabatic expansion into a vacuum Are AS AS surrounding and AStotal positive negative or zero Explain your reasoning b 2 25 moles of an ideal gas with Cv m 5R 2 are trans formed from an initial state T 680 K and P 1 15 bar to a final state T 298 K and P 4 75 bar Calculate for this pro cess AH AS

Amount of heat evolved during complete combustion of liquid benzene can be calculated from the following data i 18 gm of graphite on complete combustion evolves 591 kJ heat AH H O ii 286 kJ mol iii The heat of formation of liquid benzene is 50 kJ mole Magnitude of heat evolved in kJ from

1 In the hydrogen reduction reaction change the chemical energy given energy into electrical energy multiple of potential E and charge 2 Explain why the Gibbs energy change GG in the hydrogen reduction reaction is arbitrarily zeroed to obtain the potential of a chemical cell 3 When the standard potential of galvanic cells is 0 76 V what is the standard Gibbs energy GGO in this reaction 1 2 3 H aq e 12 H2 g E O H H2 0 2 H aq Zn s Zn2 aq H2 g E O 0 76 V

The melting points of CCl4 at various pressures are given below along with the Molar Volume change for Fusion Calculate AHfus and ASfus at 1 atm and at 4000 atm P atm 1 1000 2000 5000 7000 2 t C 22 6 15 3 48 9 130 8 176 2 AV cm mol 3 97 3 06 2 51 1 52 S 1 08 1000 OF 259 1 Meral C OG TV all

When a solution of 30 0mL of 1 0M magnesium hydroxide at 25 0 C is added to 30 0mL of 1 1 M hydrochloric at 25 0 C in a coffee cup calorimeter the temperature of the solution increases to 33 5 C Assuming that the specific heat of the solution is 4 18 J g C and that the calorimeter absorbs a negligible amount of heat The density of water is 1 00g ml 250C Please write the balanced equation and calculate the AHneutralization in kJ mol for the reaction

45 Equal masses of ethane and hydrogen are mixed in an empty container at 298 K The fraction of total pressure exerted by hydrogen is A 15 16 B 1 1 D 1 6 298 C 1 4 KATA A DRUGE SARGING B 1 1 A 15 16 C 1 4 D 1 6

By calculating ASuniv at each temperature determine if the melting of 1 mole of NaCl s is at 500 C and at 700 C spontaneous S NaCl s 72 11 mol K S NaCl 95 06 mol K kJ mol AHofusion 27 95

28 Under the same condition heats of formation of 2 water CO are 285 and 394 kJ mol respectively The heat of combustion of methane is 890 kJ mol 1 The heat of formation of methane in kJ mol is 1 964 3 222 2 890 4 74

A certain ideal gas whose R 278 6J kg K and cp 1 015 KJ kg K expand isentropically from 1517 kPa 288 C to 965 kPa For 454 g s of this gas determine a WNE b V2 c Delta U and g Delta U With Derivation of Formulas A certain ideal gas whose R 278 6 J kg K and cp 1 015 KJ kg K expand isentropically from 1517 kPa 288 C to 965 kPa For 454 g s of this gas determine a WNF b V c AU and g AU T LJ

Enthalpy changes for two reactions are given b the equation 3 2Cr s O g 2 C s O g The enthalpy Cr O3 3C 1 1460 kJ 3 800 kJ Cr O3 s AH 1130 kJ CO g AH 110 kJ change for the reactio 2Cr 3CO will be 2 800 kJ 4 1020 kJ

1 CH3COOC H5 H O CH3COOH C H5OH 2 203 30 NH H Decomposition of NH on platinum catalyst surface dil H SO4 2H0

Which of the following statement is correct 1 Entropy of egg decreases on boiling 2 Entropy of rubber band decreases on stretching 3 Entropy decreases during fusion of ice 4 All of these

400 gm of ice at 20 C is mixed with 400 gm water at 50 C then which of the following statement s is are correct Specific heat capacity value for ice and water are s ice 0 5 cal g C S water i One More Correct Answer s A B 1 cal g C and Lfusion C D Final weight of ice is 200 gm ice Final temperature of the mixture is less than 0 C Final weight of water is 600 gm 80 cal gm Weight of ice converted into water is 200 gm

1 For an ideal binary solution A and B YA is the mole fraction of A in vapour phase Which of the following plot should be linear 1 PTotalVS YA 3 P 1 VS YA 2 PTotalVS YB 1 Vs VB YA PTotal 4

9 For the conversion of water to steam at 110 C and 1 atm determine the sign 0 or for the change in Gibbs free energy the change in enthalpy and the change in entropy Please explain fully

Mixing of N and H form an ideal gas mixture at room temperature in a container For this process which of the following statements is true a AH 0 AS surrounding 0 ASsystem 0 and AG ve b AH 0 AS surrounding 0 ASsystem 0 and AG ve c AH 0 AS surrounding 0 AS system 0 and AG ve d AH 0 AS surrounding 0 ASS system 0 and AG ve e AH 0 AS surrounding 0 AS system 0 and AG ve

For the cell shown the measured cell potential Ecell is 0 3563 V at 25 C Pt s H g 0 721 atm H aq M Cd aq 1 00 M Cd s The balanced reduction half reactions for the cell and their respective standard reduction potential values E are 2H aq 2e H g Cd aq 2e Cd s Calculate the H concentration E 0 00 V E 0 403 V

Correct statement s for the ideal gas from the given graph is are 0 g 600K AP 7 CH g 400K O Average speed of CH4 g is higher than O g Average kinetic energy per mole of CH4 g is higher than that of O g O Fraction of molecules showing most probable speed is higher for O g Most probable speed of O2 g is higher than CH4 g

3 Which of the following statements are correct A Each atom has at least one orbital symmetrical about the nucleus B Each orbital has at least one orbital symmetrical about the nucleus C Number of elctrons in Ne having their angular momentum equal to zero are four D Number of waves made by an electron in an orbit is equal to number of orbit No 43

Calculate A H in units of kJ mol for the following reaction Ga O3 s 3 CO g 2 Ga s 3 CO g Use the following two reactions 2 Ga s 3 2 O g CO g O g Ga O3 s CO g AH 1077 8 kJ mol AH 282 7 kJ mol L

A monoatomic ideal gas undergoes the shown cyclic process in which path of the process 2 3 is a semicircle If 2 mol of gas is taken find Maximum temperature in the cyclic process is R V P 2Po P P 2 7 V 1 3 2V

A sample consisting of 3 mol of ideal gas molecules with Cp m 20 8 J K mol is initially at 240 kPa and 325 K It undergoes reversible adiabatic expansion until its pressure reaches 150 kPa Calculate i the final volume and temperature ii q iii w and iv AU

2 Which of the following conditions has a negative entropy Smelting gold at high pressure and high temperature Decomposition reaction of water to hydrogen and oxygen gas A perfectly crystalline material in temperature approximately near zero K An insoluble salt has a zero enthalpy of solution at room temperature

0 1 mole of an ideal monoatomic gas with Cv independent of temperature is made to undergo a reversible cyclic process consisting of the following steps State 1 1 lit 1 atm State 2 1 lit 3 atm State 2 1 lit 3 atm State 3 2 lit 3 atm State 3 2 lit 3 atm State 4 2 lit 1 atm State 4 2 lit 1 atm State 1 1 lit 1 atm Calculate q w and AE for each step and for the complete cycle Comment on ca ICI

30 At 298 K the standard enthalpies of formation of H O l and H O are 286 0 kJ mol and 188 0 kJ mol 1 The enthalpy change for reaction 2H O 1 2H O 1 O g will be 1 948 kJ mol 2 196 kJ mol 1 3 196 kJ mol 1 4 948 kJ mol 1

Three bulbs I II and III of volume V litres 2V litres and 3V litres are connected by tubes of negligible volume fitted by stopping valve as shown in fig The bulb I is at 1 atm containing 0 3 mol of H gas at temp 127 C Bulb III contains O2 gas at 77 C and pressure of 2 atm Bulb II is vacuum and maintained at temp 27 C 1 atm VL 0 3 moles of H i 127 C valve a 2VL ii 27 C valve b 3VL 02 gas 77 C iii 2 atm The valve b is opened first and then closed after some time Then the valve a is opened and closed after same time as for valve b The number of moles O2 diffused into bulb II is 0 1 mol The partial pressure in atm of H observed in bulb 1 after diffusion is

Given the following thermochemical data 4 B s 3 O2 g 2 B2O3 s 2 B s 03 g B20O3 s 1 What is AH for the reaction 2 03 g 3 02 g OA 1122 kJ OB 284 kJ OC 284 kJ OD 1122 kJ OE 5340 kJ OF 5340 kJ AH 2528 kJ AH 1406 kJ

7 Consider the following process A B AH kJ mol 1 325 kJ mol 3 525 k l mol 150 3B2C D 125 E A 2D 350 For B D E 2C AH will be AIPMT Mains 2011 2 325 kJ mol 1 175 k

3 The heat of combustion of ethanol into carbon dioxids and water is 327 kcal at constant pressure The heat evolved in cal at constant volume at 27 C if all gases behave ideally is R 2 cal mol K 36 37 Section 2 46 47 Chemistry

47 Two moles of helium gas are taken over the cycle ABCDA as shown below in the P T diagram Assume the gas to be ideal and R is gas constant 400R 2x105 P Pascal 1x 105 A 416R 300 K Floor B C 500 K 693 Temp K Now match List I with List II and select the options given below List I PY Magnitude of work done by the gas in taking from A to B Q Magnitude of work done by the gas in taking from B C R Magnitude of work done on the gas in taking from D A S 2x2 V 2 0 0121 30 Clash 300 k Magnitude of the net heat absorbed evolved in the cycle ABCDA 1 693 R 2 277 R 3 400 R 4 416 R ISOR List II 24 63 1 S

A aq B aq AB aq The reaction shown above is carried out in a coffee cup calorimeter The reaction occurs in 350 0 of solution initially at 22 6 C The temperature of the solution increases to 50 7 C when the reaction is carried out using 0 495 mol of A Calculate the enthalpy change for the reaction AH i kJ mol Enter a numerical value in the box provided in 3 significant figures including the proper sign Assume that the specific heat capacity of the solution is 4 18 J g C

H g C H4 g C H6 g AG 98 0 kJ and AS 120 7 J K at 323 K and 1 atm The maximum amount of work that could be done by this reaction when 2 10 moles of H g react at standard conditions at this temperaturo in 22k L

4 Calculate the change in the entropies of the system and the surroundings and the total change in entropy when a sample of nitrogen gas of mass 14 g at 298 K and 1 00 bar doubles its volume in a an isothermal reversible expansion b an isothermal 0 and c an adiabatic irreversible expansion against pext reversible expansion

Consider the reaction A s B s C g anc the following thermodynamic data at 298 K Substance AH kJ mol AG kJ mol 1034 33 1020 02 845 02 650 93 462 83 576 77 A s B s C g Pc at 1230 44 K in bar

IE and IE of Mg are 178 and 348 kcal mol respectively The energy required for the reaction Mg g Mg 2e is 2 1 a 170 kcal mol c 170 kcal mol b 526 kcal mol d 525 kcal mol