4131 + Interview Questions in THERMODYNAMICS IN GENERAL AWARENESS Page 79 InterviewSolution

3901.	How does internal energy of a gas change in adiabatic expansion?A. `DeltaU=0`B. `DeltaU=`negativeC. `DeltaU=`positiveD. `DeltaW=`zero
Answer» Correct Answer - B

Discussion

3902.	The pressure in the tyre of a car is four times the atmospheric pressure at 300 K. if this tyre suddenly bursts, Its new temperature will the `(gamma=1.4)`A. `300(4)^(1.4//0.4)`B. `300((1)/(4))^(1.4//0.4)`C. `300(2)^(-1.4//0.4)`D. `300(4)^(-1.4//0.4)`
Answer» Correct Answer - D

Discussion

3903.	(a) A certain mass of gas initially at `(1L, 5 atm, 300 K)` is expanded reversible and isothermally to final volume of `5L`, calculate the work done by the gas and heat supplied in this process to the gas. (b) Now, if the gas is released to initial position by compressing it using an external constant pressure of `5` atm. Fins work done on the gas in this process and heat rejected by gas (c ) In the above two processes, what is the net gained by surroundings ? [Note: From above question see that surrounding has done extra work on the system but system has returned that work in the form of heat to surrounding and work is considered on organized form of energy while heat as an unorganised form hence in the above process, there must be net increment in randomness of universe which be called Entropy, soon]
Answer» `PV=nRT " " rArr5xx1=nxx0.82xx300 " "rArrn=0.203` (a) `{:("Initial",,,,"Final"),(V=1L,,,,V_(2)=5L),(P=5atm,,,,),(T=300K,,,,T=300K):}` `w= -2.303 nRT "log "(V_(2))/(V_(1))= -2.303xx0.203xx8.314xx300 log 5= -816J` `w= -816J` and `q= -w=816 J` So, work done by the gas `=816 J` (b) `w= -P_(ext)(V_(2)-V_(1))= -5[1.5]= +20xx101.325` `w=2026 J` (c ) `q_(1)= -w_(1)= +816 J` `q_(2)= -w_(2)= -2026 J` `q_(1)+q_(2)= -1210 J` So, Net heat released by the system `= -1210`

Discussion

3904.	Discuss whether the following phenomena are reversible? (i) Water fall (ii) Rusting of iron (iii) Electrolysis.
Answer» (i) Water fall : The falling of water is not a reversible process. During the fall of water, the major part of its potential energy is converted into kinetc energy of water. On strinking the ground , a part of it is converted into heat and sond energy. It is not possible to convert the heat and sound produced along with the `K.E` of water into potential energy so as to make the water rise back to the initial height. Therefore, water fall is not a reversible process. (ii) Rusting of Iron: In the rusting of irion, the iron gets oxidised by the oxygen from the air. Since it is a chemical change, it is not a reversible process. (iii) Electrolysis: It is a reversible process provided the resistance of the electrolyte to the flow of current is zero. On reversing the direction of current, the direction of motion of ions is reversed.

Discussion

3905.	Is rusting of iron a reversible process?
Answer» No, rusting of iron is irreversible process.

Discussion

3906.	A gas contained in a cylinder fitted with a frictionless piston expands against a constant pressure 1 atmosphere from a volume of 4 litre to a volume of 14 litre. In doing so, it absorbs 800 J thermal energy from surroundings. Determine `DeltaU` for the process.A. `-213.7 J`B. `-112 J`C. `-50 J`D. `-25 J`
Answer» Correct Answer - A `W=-2.303 nRT "log" V_(2)/V_(1)`

Discussion

3907.	For adiabatic expansion of an ideal gasA. `PV ^(gamma) =`constantB. `TV^(gamma -1) = ` constantC. `TP ^(1- gamma) = ` const.D. `TP^( 1//gamma) = `constant
Answer» Correct Answer - a,b (c ) and (d) are wrong. The correct relation is `TP ^((1-gamma)/(gamma))= ` constant

Discussion

3908.	Which of the following relationship are correct?A. `( DeltaH- DeltaE)/( DeltanxxT ) =`ConstantB. `DeltaG= -T DeltaS_("Total")`C. `K= e^(- DeltaG^(@) //RT)`D. `[(del(DeltaH))/(delT)]_(P)= DeltaC_(p)`
Answer» Correct Answer - a,b,c,d (a) followsfrom `DeltaH = DeltaE +Deltan RT`. (b) is well known relationship (c ) is wrong because `DeltaU = q+w` (d) follows from `- DeltaG^(@) = RT ln K`. (e ) represents Kirchhoff equation.

Discussion

3909.	In the dissociation of `CH_(4)`,minimum energy is required in the ______ step.A. fourthB. thirdC. secondD. first
Answer» Correct Answer - A Because the bond broken in the fourth step has minimum percentage of `s` character.

Discussion

3910.	Heats of formation of `SiO_(2)` and `MgO` are `-48.24` and `-34.7` kJ respectively. The heat of the reaction : `2Mg+SiO_(2) rarr 2MgO+Si` isA. `21.64 kJ`B. `-21.16 kJ`C. `-13.62 kJ`D. `13.62 kJ`
Answer» Correct Answer - B `DeltaH=H_(P)-H_(R)`

Discussion

3911.	The buring of magnesium may be represented by: `2Mg(s) +O_(2)(g) rarr 2MgO(s), DeltaH^(Theta) =- 1204 kJ (mol O_(2))^(-1)` Which one of the following correctly descride what would happen if the reaction were allowed to proceed at constant external pressure in such a way that no enegry transfer could taken place between the reaction mixture and its surroundings?A. No reaction could occur.B. The tempertaure of the reaction mixture would increase.C. The temperature of the reaction mixture would decrease.D. The pressure of the system would increase.
Answer» In combustion, heat evolved, hence temperature of system will increase.

Discussion

3912.	Which of the following statement (s) is correct? Statement-I: The entropy of isolated system with P-V work only, is always maximized at equillibrium. Statement-2: It is possible for the entropy of closed system to decrease substantialy in an irreversible process. Statemet-3: Entropy can be crearted but not destroyed. Statement-4 `DeltaS_(system)` is zero for reversible process in an isolated system.A. Statement i, ii, iiiB. Statement ii, ivC. Statement I, ii, iiiD. None of these
Answer» Correct Answer - D

Discussion

3913.	Which of the following statement (s) is correct? Statement-I: The entropy of isolated system with P-V work only, is always maximized at equillibrium. Statement-2: It is possible for the entropy of closed system to decrease substantialy in an irreversible process. Statemet-3: Entropy can be crearted but not destroyed. Statement-4 `DeltaS_(system)` is zero for reversible process in an isolated system.A. Statement 1,2,3B. Statement 2,4C. Statemetn 1,2,4D. All of these
Answer» Correct Answer - D

Discussion

3914.	Which of the following statement(s) is /are correct: Statement (a): The entropy of isolated system with P-V work only is always maximized at equilibrium Statement (b) : It is possible for the entropy of closed system to decrease substanilly in a irreverrsible process. Statement (c): Entrophy can be created but not destrpoyed . Statment (d) : `DeltaS_(system)` is always zero for reversible processe in an isolated systemA. Statement a, b, cB. Statement b,dC. Staement a,b,cD. All
Answer» Correct Answer - D

Discussion

3915.	Which of the following option the first compound has less entropy than second:A. `(i)` aqueous solution of `1 "M of" MgCI_(2) (ii)` aqueous solution of `1 "M of" NaCI`B. `(1) Br_(2)` liquid at `25^(@) (ii) Br_(2)` liquid at `20^(@)C`C. `(i) HgO` solid `(ii) HgS` solidD. `(i) Br_(2)` liquid `(ii) I_(2)` solid
Answer» Correct Answer - C

Discussion

3916.	During winters , moisture condenses in the form of dew and can be seen on plant leaves and grass, The entropy of the system in such cases decreases as liquids process lesser disorder as compared to gases. With reference to the second law, which statement is correct , for the above process?A. The randomeness of the universe decreasesB. The randomness of the surrounding decreasesC. Increase is randomness of surrounding equals to the decrease in randomness of systemD. The increase in randomness of the surroundings in greater as compared to the decrease in randomness of the system.
Answer» Correct Answer - D As dew formation is spontaneous process, therefore, entrophy or randomness of the universe will increase. As randomeness of the system has decreased but randomness of the surrounding will increase larger so that change is positive.

Discussion

3917.	During winters, moisture condness in the form of dew and can be seen on plant leaves and grass. The entropy of the system in such cases decreases as liquids posses lesser disorder compared to gases. With prefrence to the second law, which statement is correct, for the above proces?A. The randomnes of the unierse decreases.B. The randomnesof the surroundings decreases.C. Increases is randomne of surrroundings equals the decreases in randomnes of system.D. The increase in randomnes of the surrounding is greater as compared to the decrease in randomnes of the system.
Answer» Correct Answer - D

Discussion

3918.	For the gas phase reaction `PCl_(5)rarrPCl_(3)(g)+Cl_(2)(g)` which of the following conditions are correct?A. `Delta H lt 0` and `Delta S lt 0`B. `Delta H gt 0` and `Delta S lt 0`C. `Delta H = 0` and `Delta S lt 0`D. `Delta H gt 0` and `Delta S lt 0`
Answer» Correct Answer - D

Discussion

3919.	Consider the following reactions: `C(s)+O_(2)(g)toCO_(2)(g)+x " kJ"` `CO(g)+(1)/(2)O_(2)(g)toCO_(2)(g)+y" kJ"` The heat formation of CO(g) is :A. `-(x+y)" kJ"//mol`B. (x-y) kJ`//`molC. (y-x) kJ`//` molD. None of these
Answer» Correct Answer - C

Discussion

3920.	The enthalpy change for the following reaction is 368 kJ. Calculate the average O-F bond energy. `OF_(2)(g)rarrO(g)+2F(g)`A. 184 kJ/molB. 368 kJ/molC. 536 kJ/molD. 736 kJ/mol
Answer» Correct Answer - A `(O-F)=(368)/(2)=184`

Discussion

3921.	A 10.00g piece of metal is heated to `80.00^(@)C` and placed in 100.0g of water at `23.00^(@)C`. When the system has reached eqvillibrium the temperature of the water and metal are `23.50^(@)C`. What is the identify of the metal? `"Specify heat capacity of" H_(2)O=4.184J//g overset(@)C`A. `Ag(C_(p) 0.236 J//g overset(@)C)`B. `Cu(C_(p) 0.385 J//g overset(@)C)`C. `Fe(C_(p) 0.385 J//g overset(@)C)`D. `Al(C_(p) 0.385 J//g overset(@)C)`
Answer» Correct Answer - B

Discussion

3922.	The heat conductivity of helium is `8.7` times that of argon (under standard conditions). Find the radio of effective diameters of argon and helium atoms.
Answer» `k = (1)/(3) lt v gt lamda rho c_v` =`(1)/(3) sqrt((8 kT)/(m pi)) (1)/(sqrt(2) pi d^2 n) mn (C_V)/(M)` `(C_V` is the specific heat capacity which is `(C_V)/(M) )`. Now `C_V` is the same for all monoatomic gases such as `He` and `A`. Thus `k alpha (1)/(sqrt(M) d^2)` or `(k_(He))/(k_A) = 8.7 = (sqrt(M_A) d_A^2)/(sqrt(M_(He) d_H^2)) = sqrt(10) (d_A^2)/(d_(He)^2)` `(d_A)/(d_(He)) = sqrt((8.7)/(sqrt(10))) = 1.658 ~~ 1.7`.

Discussion

3923.	Under standard conditions helium fills up the space between two long coaxial cylinders. The mean radius of the cylinders is equal to `R`, the gap between them is equal to `Delta R`, with `Delta R lt lt R`. The outer cylinder rotates with a fairly low angular velocity `omega` about the stationary inner cylinder. Down to what magnitude should the helium pressure be lowered (keeping the temperature constant) to decrease the sought moment of friction forces `n = 10` times if `Delta R = 6 mm` ?
Answer» In this case `N_1 (r_2^2 - r_1^2)/(r_1^2 r_2^2) = 4 pi eta omega` or `N_1 (2 R Delta R)/(R^4) ~~ 4 pi eta omega` or `N_1 = (2 pi eta omega r^3)/(Delta R)` To decrease `N_1, n` times `eta` must be decreased `n` times. Now `eta` does not depend on pressure until the pressure is so low that the mean free path equals, say, `(1)/(2) Delta R`. Then the mean free path is fixed and `eta` decreases with pressure. The mean free path equals `(1)/(2) Delta R` when `(1)/(sqrt(2) pi d^2 n_0) = Delta R(n_0 = concentration)` Corresponding pressure is `p_0 = (sqrt(2) kT)/(pi d^2 Delta R)` The sought pressure is `n` times less `p = (sqrt(2) k T)/(pi d^2 n Delta R) = 70.7 xx (10^-23)/(10^-18 xx 10^-3) ~~ 0.71 Pa` the answer is qualitative and depends on the choice `(1)/(2) Delta R` for the mean free path.

Discussion

3924.	Two identical parallel discs have a common axis and are located at a distance `h` from each other. The radius of each disc is equal to `q`, with `a gt gt h`. One disc is rotated with a low angular velocity `omega` relative to the other, stationary, disc. Find the moment of friction forces acting on the stationary disc if the viscosity coefficient of the gas between the disc is equal to `eta`.
Answer» We consider two adjoining layers. The angular velocity gradient is `(omega)/(h)`. So the moment of the frictional force is `N = int_0^a r.2 pi r dr.eta r (omega)/(h) = (pi eta a^4 omega)/(2 h)`.

Discussion

3925.	A gas fills up the space between two long coaxial cylinders of radii `R_1` and `R_2`, with `R_1 lt R_2`. The outer cylinder rotates with a fairly low angular velocity `omega` about the stationary inner cylinder. The moment of friction forces acting on a unit length of the inner cylinder is equal to `N_1`. Find the viscosity coefficient `eta` of the gas taking into account that the friction force acting on a unit area of the cylindrical surface of radius `r` is determined by the formule `sigma = eta r(del omega//del r)`.
Answer» We neglect the moment of inertia of the gas in a shell. Then the moment of friction forces on a unit length of the cylinder must be a constant as a function of `r`. So, `2 pi r^3 eta (d omega)/(dr) = N_1` or `omega (r) = (N_1)/(4 pi eta) ((1)/(r_1^2) -(1)/(r^2))` and `omega = (N_1)/(4 pi eta) ((1)/(r_1^2) -(1)/(r_2^2))` or `eta = (N_1)/(4 pi omega) ((1)/(r_1^2) -(1)/(r_2^2))`.

Discussion

3926.	Explain the meaning of the thermochemical equation for the reaction. 2H2(g) + O2(g) → 2H2O(l) +136 kcal.
Answer» When two moles i.e., 4 grams of gaseous H₂ reacts with 1 mole (32g) of gaseous O₂ to give 2 moles of liquid water i.e., 36 gram of liquid water, 136 kcal of heat is liberated.

Discussion

3927.	A thermodynamic system is taken through the cyclic `PQRSP` process. The net work done by the system is A. 2PVB. 20 jC. `-20 j`D. `400j`
Answer» Correct Answer - B

Discussion

3928.	In an isobaric process, the ratio of heat supplied to the system `(dQ)` and work done by the system `(dW)` for diatomic gas isA. `1:1`B. `7:2`C. `7:5`D. `5:7`
Answer» Correct Answer - B

Discussion

3929.	`DeltaG^(@)` for a reaction `25^(@)C is 3.5kJ xx mol^(-1)`. What is the value of K?A. `2.2 xx 10^(5)`B. `1.1`C. `0.86`D. `4.5 xx 10 ^(-6)`
Answer» Correct Answer - D

Discussion

3930.	If for a chemical reaction `Delta C_(p)` I stemperature of reactants of this reaction bya certain amount =`q_(1)` and heat required to increase temperature of products of the same reaction by same amount =`q_(2)`, then:A. `q_(1)gtq_(2)`B. `q_(1)ltq_(2)`C. `q_(1)=q_(2)`D. `q_(1)` may or may not be equal to `q_(2)` will depend on nature of reactants and products .
Answer» Correct Answer - a

Discussion

3931.	Calculate the amount of heat released at constant pressure when 10 moles of carbon react with 6 moles of `O_(2)` leaving none of the reactants. `DeltaH_("combustion")C_(("graphite"))=-390KJ//"mole",` `DeltaH_("combustion")CO(g)=-250KJ//"mole"`A. 1900KJB. 750KJC. 3900KJD. 2450KJ
Answer» Correct Answer - a

Discussion

3932.	`DeltaH` and `DeltaU` are the same of the reaction, `N_(2)(g)+O_(2)(g)iff2NO(g)`, All reactants and products are gases where all gases are ideal.A. If both the statements are TRUE and STATEMENT-2 is the correct explanation of STATEMENT-1B. If both the statements are TRUE but STATEMENT-2 is NOT the correct explanation of STATEMENT-1C. If STATEMENT-1 is TRUE and STATEMENT-2 is FALSED. If STATEMENT-1 is FALSE and STATEMENT-2 is TRUE
Answer» Correct Answer - B

Discussion

3933.	Two cyclinder A and B of equal capacity are connected to eachother via a stopcock. The cyclinder A contains an ideal gas at standard temperature and pressure, while the cyclindr B is completely evacuated. The entire system is thermally insulated. The stopcock is suddenly opened. Answer the following: (a) What is the final pressure of the gas in A and B? (b) What is the change in internal energy of the gas? (c ) What is the change in temperature of a gas? (d) Do the intermidiate states of the system (before settling to the final equilibrium state)lie on its `P-V-T` surface?
Answer» (a) When a stopcock is suddenly opened, the volume available to the gas at 1 atmosphere pressure will become two times. Therefore, pressure will decrease to one half, i.e., `0.5` atmosphere. (b) There will be no change in the internal energy of the gas as no work is done on//by the gas. (c) Also, there will be no change in temperture of the gas as gas does not work in expansion. (d) No, because the process called free expansion is rapid and cannot be controlled. The intermediates states are non-equilibrium staes and do not satisfy the gas equation. In due course, the gas does return to an equilibrium state.

Discussion

3934.	Statement-1 : Change in internal energy in the melting process is due to change in internal potential energy. Statement-2 : This is because in melting, distance between molecules increases but temperature remains constant.A. If both, Assertion and Reason are true and Reason is the correct explanation of the Asserrion.B. If both,Assertion and Reason are true but Reason is not a correct explanation of the Assertion.C. If Assertion is true but the Reason is false.D. If both, Assertion and Reason are false.
Answer» Correct Answer - A In an adiabatic process, no exchange of heat is permissible i.e., `dQ=0`. As `dQ=dU+dW=0 :. dU= -dW` Statement-1 is true. Statement-2 is true and statement- 2 is correct explanation of statement-1

Discussion

3935.	Statement-1 : Heat from the sun reaches the earth by convection. Statement-2 : Air can be heated only by convectionA. If both, Assertion and Reason are true and Reason is the correct explanation of the Asserrion.B. If both,Assertion and Reason are true but Reason is not a correct explanation of the Assertion.C. If Assertion is true but the Reason is false.D. If both, Assertion and Reason are false.
Answer» Correct Answer - D Heat from sun reaches us by radiation. Air between is not heated. Air can be heatd only by convection Statement-1 is false. Statement-2 is true.

Discussion

3936.	Which is a good fuel`CH_(4)` or`C_(2)H_(6)` ? The standard enthalpy of formation of `CH_(4), C_(2)H_(6), CO_(2)` and `H_(2)O` are `- 74.8, - 84.6 , - 393 . 5` and `-286kJ mol^(-1)` respectively.
Answer» Correct Answer - `CH_(4)` Calculate `Delta H `for `CH_(4) + 2O_(2) rarr CO_(2)+ 2H_(2)O` and `C_(2)H_(6) + (7)/(2) O_(2) rarr 2CO_(2)+ 3H_(2)O` Then calculate `Delta H ` per gram

Discussion

3937.	One method to produce hydrogen on an industrial on an industrial scale is the reaction of methane with overheated water vapour at 1100 K to form hydrogen and carbon monoxide . The reaction is known as steam reforming Calcuate the pressure in the vessel at 1100K and the % conversion of methane.
Answer» Correct Answer - Total pressure at 1100K =6.550 bar Conversion (methene) `~~ 49%`

Discussion

3938.	The internal energy of an ideal gas increases during an isothermal process when the gas isA. Expanded by adding more molecules to itB. Expanded by adding more heat to itC. Expanded against zero pressureD. Compressed by doing work on it
Answer» Correct Answer - A

Discussion

3939.	A gaseous mixture enclosed in a vessel of volume `V` consists of one gram mole of gas `A` with `gamma = (C_(P))/(C_(V)) = (5)/(3)`an another gas `B` with `gamma = (7)/(5)` at a certain temperature `T`. The gram molecular weights of the gases `A` and `B` are `4` and `32` respectively. The gases `A` and `B` do not react with each other and are assumed to be ideal. The gaseous mixture follows the equation `PV^(19//13)` = constant , in adiabatic process. Find the number of gram moles of the gas `B` in the gaseous mixture.A. 2B. 3C. 4D. 5
Answer» Correct Answer - A Let the number of moles of gas B=n The number of moles of gas A=1 Since `U=(nRT)/(gamma-1)` For mixture, `U=U_(m),gamma=(19)/(13)` `therefore U_(m)=U_(A)+U_(B)` `therefore (n_(A)+n_(B)RT)/(gamma_(m)-1)=(n_(A)RT)/(gamma_(A)-1)+(n_(B)RT)/(gamma_(B)-1)` or `(1+n)/((19)/(13)-1)=(1)/((5)/(3)-1)+(n)/((7)/(5)-1)` or `(13(1+n))/(6)=(3)/(2)+(5n)/(2)or 13+13n=9+15n` or 4=2n or n=2

Discussion

3940.	In a chemical reaction, `Delta H = 150 kJ and Delta S = 100 JK^(-1)` at 300 K. Therefore, `Delta`G will beA. ZeroB. 300 kJC. 330 kJD. 120 kJ
Answer» Correct Answer - D

Discussion

3941.	Pick out the correct option which represents for the work done by the system on the surroundingsA. `p_("in") gt p_("ex")`B. `p_("in") = p_("ex")`C. `p_("in") lt p_("ex")`D. `p_("ex") ge 1` atm
Answer» Correct Answer - A

Discussion

3942.	18.0 g of water completely vaporises at `100^(@)C` and 1 bar pressure and the enthalpy change in the process is40.79 kJ `mol^(-1)`. What will be the enthalpy change for vaporising two moles of water under the same conditions ? What is the standard enthalpy of vaporisation for water ?
Answer» `18.0` g of water `=` 1 mole `:. ` Standard enthalpy of vaporisation at`100^(@)C` and 1 bar pressure `=40.79 kJ mol^(-1)` Enthalpy change in vaporisationof 2 moles of water `= 2 xx 40.79 kJ = 81. 58 kJ`

Discussion

3943.	`X(g) + 2Y(g) rarr 2Z(g) + 3A(g)` The change in enthalpy at `27^(@)C` is 79.5 kJ. The value of `Delta`U isA. 74.5 kJB. 4.99 kJC. 79.5 kJD. 75.9 kJ
Answer» Correct Answer - A

Discussion

3944.	The free energy change, `Delta`G = 0, whenA. The reactants are completely consumedB. A catalyst is addedC. The system is at equilibriumD. The reactants are initially start reacting
Answer» Correct Answer - C

Discussion

3945.	The following are the `P-V` diagram for cyclic process for a gas. In which of these processes, heat is not obsorbed by the gas?A. B. C. D.
Answer» In `(d)` process is not cyclic.

Discussion

3946.	At `25^(@)C`, the following heat of formations are given: `{:("Compound",SO_(2)(g),H_(2)O(l),,),(Delta_(f)H^(Theta)kJmol^(-1),-296.0,-285.0,,):}` For the reactions at `25^(@)C`, `2H_(2)S(g) +Fe(s) rarr FeS_(2)(s) +2H_(2)(g), DeltaH^(Theta) =- 137 kJ mool^(-1)` `H_(2)S(g) +(3)/(2)O_(2)(g) rarr H_(2)O(l) +So_(2)(g),DeltaH^(Theta) =- 562kJ mol^(-1)` Calculate the heat of formation of `H_(2)S(g)` and `FeS_(2)(g)` at `25^(@)C`.
Answer» `4C(s)+5H_(2)+SrarrH-overset(H)overset(\|)underset(H)underset(\|)(C)-overset(H)overset(\|)underset(H)underset(\|)(C)-S-overset(H)overset(\|)underset(H)underset(\|)(C)-overset(H)overset(\|)underset(H)underset(\|)(C)-H` `4C(s)+5H_(2)+2SrarrH-overset(H)overset(\|)underset(H)underset(\|)(C)-overset(H)overset(\|)underset(H)underset(\|)(C)-S-S-overset(H)overset(\|)underset(H)underset(\|)(C)-overset(H)overset(\|)underset(H)underset(\|)(C)-H` `DeltaH = sum(BE)_(R)-sum(BE)_(P)` a. `-147.2 =` Heat of atomisation of `4C,10H,1S -BE` of `10(C -H), 2(C-S), 2(C-C)` b. `-201.9 =`Heat of atomization of `4C, 10H, 2S - BE of 10(C-H), 2(C-S), 2(C-C), (S-S)` Subtracting equations (i) from (ii), we get `-201.9 +14.2 =`Heat of atomisation of `1S -BE of (S-S)` `= 22.8 kJ -BE of (S-S)` `BE of (S-S) = 277.5 kJ`

Discussion

3947.	In the cyclic process shown on `P_V` diagram, the magnitude of the work done is A. `pi((P_(2)-P_(1))/(2))^(2)`B. `pi((V_(2)-V_(1))/(2))^(2)`C. `(pi)/(4) (P_(2)-P_(1)) (V_(2)-V_(1))`D. `pi(P_(2)V_(2) = P_(1)V_(1))`
Answer» Work done `=` Area under the curve Area of sphere `= pir^(2) = pi = pi((V_(2)-V_(1))^(2))/(2) (r=(V_(2)-V_(1))/(2))` `=(pi(P_(2)^(2)-P_(1))^(2))/(2) (r =(P_(2)-P_(1))/(2))` `:. `(b) and (a)

Discussion

3948.	A gas expands isothermally against a constant external pressure of 1 atm from a volume of 10 `dm^(3)` to a volume of 20 `dm^(3)`. It absorbs 800 J of thermal energy from its surroundings. The `Delta`U isA. `-312` JB. `+123` JC. `+312` JD. `-213` J
Answer» Correct Answer - D

Discussion

3949.	For a reaction `M_(2)O_((g))to2M_((s))+1/2O_(2(g))`, `DeltaH=30 k J mol^(-1)` and `DeltaS=0.07 k J mol^(-1)` at `1 atm`. Calculate up to which temperature, the reaction would not be spontaneous.
Answer» Correct Answer - `T < 428.57 K`

Discussion

3950.	Bond dissociation enthalpies of `H_(2)(g)` and `N_(2)(g)` are `436.0 kJ mol^(-1)` and `941.8 kJ mol^(-1)`, respectively, and ethalpy of formation of `NH_(3)(g)` is `-46kJ mol^(-1)`. What is the enthalpy fi atomisation of `NH_(3)(g)`?. What is the avergae bond ethalpy of `N-H` bond?
Answer» `N_(2)(g) +3H_(2)(g) rarr 2NH_(3)(g),DeltaH =-2 xx 46 kJ mol^(-1)` `DeltaH = sum(BE)_(R) -sum(BE)_(P)` `=(941.8 +3 xx 436) - (6x) =- 2 xx 46` (Here `x = BE` of `N-H` bonds) `x = 390.3 kJ mol^(-1)` `NH_(3) rarr N +3(H)` Heat of atomisaiton `=3xx 390.3 = 1170.9 kJ mol^(-1)`

Discussion

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How does internal energy of a gas change in adiabatic expansion?A. `DeltaU=0`B. `DeltaU=`negativeC. `DeltaU=`positiveD. `DeltaW=`zero

The pressure in the tyre of a car is four times the atmospheric pressure at 300 K. if this tyre suddenly bursts, Its new temperature will the `(gamma=1.4)`A. `300(4)^(1.4//0.4)`B. `300((1)/(4))^(1.4//0.4)`C. `300(2)^(-1.4//0.4)`D. `300(4)^(-1.4//0.4)`

Discuss whether the following phenomena are reversible? (i) Water fall (ii) Rusting of iron (iii) Electrolysis.

Is rusting of iron a reversible process?

For adiabatic expansion of an ideal gasA. `PV ^(gamma) =`constantB. `TV^(gamma -1) = ` constantC. `TP ^(1- gamma) = ` const.D. `TP^( 1//gamma) = `constant

Which of the following relationship are correct?A. `( DeltaH- DeltaE)/( DeltanxxT ) =`ConstantB. `DeltaG= -T DeltaS_("Total")`C. `K= e^(- DeltaG^(@) //RT)`D. `[(del(DeltaH))/(delT)]_(P)= DeltaC_(p)`

In the dissociation of `CH_(4)`,minimum energy is required in the ______ step.A. fourthB. thirdC. secondD. first

Heats of formation of `SiO_(2)` and `MgO` are `-48.24` and `-34.7` kJ respectively. The heat of the reaction : `2Mg+SiO_(2) rarr 2MgO+Si` isA. `21.64 kJ`B. `-21.16 kJ`C. `-13.62 kJ`D. `13.62 kJ`

For the gas phase reaction `PCl_(5)rarrPCl_(3)(g)+Cl_(2)(g)` which of the following conditions are correct?A. `Delta H lt 0` and `Delta S lt 0`B. `Delta H gt 0` and `Delta S lt 0`C. `Delta H = 0` and `Delta S lt 0`D. `Delta H gt 0` and `Delta S lt 0`

Consider the following reactions: `C(s)+O_(2)(g)toCO_(2)(g)+x " kJ"` `CO(g)+(1)/(2)O_(2)(g)toCO_(2)(g)+y" kJ"` The heat formation of CO(g) is :A. `-(x+y)" kJ"//mol`B. (x-y) kJ`//`molC. (y-x) kJ`//` molD. None of these

The enthalpy change for the following reaction is 368 kJ. Calculate the average O-F bond energy. `OF_(2)(g)rarrO(g)+2F(g)`A. 184 kJ/molB. 368 kJ/molC. 536 kJ/molD. 736 kJ/mol

The heat conductivity of helium is `8.7` times that of argon (under standard conditions). Find the radio of effective diameters of argon and helium atoms.

Explain the meaning of the thermochemical equation for the reaction. 2H2(g) + O2(g) → 2H2O(l) +136 kcal.

A thermodynamic system is taken through the cyclic `PQRSP` process. The net work done by the system is A. 2PVB. 20 jC. `-20 j`D. `400j`

In an isobaric process, the ratio of heat supplied to the system `(dQ)` and work done by the system `(dW)` for diatomic gas isA. `1:1`B. `7:2`C. `7:5`D. `5:7`

`DeltaG^(@)` for a reaction `25^(@)C is 3.5kJ xx mol^(-1)`. What is the value of K?A. `2.2 xx 10^(5)`B. `1.1`C. `0.86`D. `4.5 xx 10 ^(-6)`

Calculate the amount of heat released at constant pressure when 10 moles of carbon react with 6 moles of `O_(2)` leaving none of the reactants. `DeltaH_("combustion")C_(("graphite"))=-390KJ//"mole",` `DeltaH_("combustion")CO(g)=-250KJ//"mole"`A. 1900KJB. 750KJC. 3900KJD. 2450KJ

Which is a good fuel`CH_(4)` or`C_(2)H_(6)` ? The standard enthalpy of formation of `CH_(4), C_(2)H_(6), CO_(2)` and `H_(2)O` are `- 74.8, - 84.6 , - 393 . 5` and `-286kJ mol^(-1)` respectively.

One method to produce hydrogen on an industrial on an industrial scale is the reaction of methane with overheated water vapour at 1100 K to form hydrogen and carbon monoxide . The reaction is known as steam reforming Calcuate the pressure in the vessel at 1100K and the % conversion of methane.

The internal energy of an ideal gas increases during an isothermal process when the gas isA. Expanded by adding more molecules to itB. Expanded by adding more heat to itC. Expanded against zero pressureD. Compressed by doing work on it

In a chemical reaction, `Delta H = 150 kJ and Delta S = 100 JK^(-1)` at 300 K. Therefore, `Delta`G will beA. ZeroB. 300 kJC. 330 kJD. 120 kJ

Pick out the correct option which represents for the work done by the system on the surroundingsA. `p_("in") gt p_("ex")`B. `p_("in") = p_("ex")`C. `p_("in") lt p_("ex")`D. `p_("ex") ge 1` atm

18.0 g of water completely vaporises at `100^(@)C` and 1 bar pressure and the enthalpy change in the process is40.79 kJ `mol^(-1)`. What will be the enthalpy change for vaporising two moles of water under the same conditions ? What is the standard enthalpy of vaporisation for water ?

`X(g) + 2Y(g) rarr 2Z(g) + 3A(g)` The change in enthalpy at `27^(@)C` is 79.5 kJ. The value of `Delta`U isA. 74.5 kJB. 4.99 kJC. 79.5 kJD. 75.9 kJ

The free energy change, `Delta`G = 0, whenA. The reactants are completely consumedB. A catalyst is addedC. The system is at equilibriumD. The reactants are initially start reacting

The following are the `P-V` diagram for cyclic process for a gas. In which of these processes, heat is not obsorbed by the gas?A. B. C. D.

In the cyclic process shown on `P_V` diagram, the magnitude of the work done is A. `pi((P_(2)-P_(1))/(2))^(2)`B. `pi((V_(2)-V_(1))/(2))^(2)`C. `(pi)/(4) (P_(2)-P_(1)) (V_(2)-V_(1))`D. `pi(P_(2)V_(2) = P_(1)V_(1))`

A gas expands isothermally against a constant external pressure of 1 atm from a volume of 10 `dm^(3)` to a volume of 20 `dm^(3)`. It absorbs 800 J of thermal energy from its surroundings. The `Delta`U isA. `-312` JB. `+123` JC. `+312` JD. `-213` J

For a reaction `M_(2)O_((g))to2M_((s))+1/2O_(2(g))`, `DeltaH=30 k J mol^(-1)` and `DeltaS=0.07 k J mol^(-1)` at `1 atm`. Calculate up to which temperature, the reaction would not be spontaneous.

Bond dissociation enthalpies of `H_(2)(g)` and `N_(2)(g)` are `436.0 kJ mol^(-1)` and `941.8 kJ mol^(-1)`, respectively, and ethalpy of formation of `NH_(3)(g)` is `-46kJ mol^(-1)`. What is the enthalpy fi atomisation of `NH_(3)(g)`?. What is the avergae bond ethalpy of `N-H` bond?