540 + Interview Questions in CHEMICAL-THERMODYNAMICS IN GENERAL AWARENESS Page 5 InterviewSolution

201.	Calculate the enthalpy change for the following reaction: `CH_(4)(g)+2O_(2)(g)toCO_(2)(g)+2H_(2)O(l)` given, enthalpies of formation of `CH_(4),CO_(2) and H_(2)O` are `-74.8kJ` `mol^(-1),-393.5kJ" "mol^(-1) and -286.2kJ" "ml^(-1)` respectively.
Answer» `DeltaH^(@)=DeltaH_(f("products"))^(@)-DeltaH_(f("reactants"))^(@)` `=[DeltaH_(f(CO_(2)))^(@)+2DeltaH_(f(H_(2)O))^(@)]-[DeltaH_(f(CH_(4)))^(@)+2DeltaH_(f(O_(2)))^(@)]` `=[-393.5+2xx(-286.2)]=[-74.8+2xx0]` `=-393.5-572.4+74.8` `=891.1kJ`

Discussion

202.	The enthalpies of formation of `Al_(2)O_(3)` and `Cr_(2)O_(3)` are `-1596KJ` and `-1134KJ` respectively. `DeltaH` for the reaction `2Al+Cr_(2)O_(2)rarr2Cr+Al_(2)O_(3)` isA. `-2730KJ`B. `-462KJ`C. `-1365KJ`D. `+2730KJ`
Answer» Correct Answer - D `2Al+(3)/(2)O_(2)rarrAl_(2)O_(3),DeltaH=-1596KJ" "…(i)` `2Cr+(3)/(2)O_(2)rarrCr_(2)O_(3),DeltaH=-1134KJ" " …(ii)` By (i),, (ii) `2Al+Cr_(2)O_(3)rarr2Cr+Al_(2)O_(3),DeltaH=-462KJ`

Discussion

203.	The enthalpies for the following reactions `(DeltaH^(Theta))` at `25^(@)C` are given below. a. `(1)/(2)H_(2)(g) +(1)/(2)O_(2)(g) rarr OH(g)` `DeltaH = 10.06 kcal` b. `H_(2)(g) rarr 2H(g), DeltaH = 104.18 kcal` c. `O_(2)(g) rarr 2O(g), DeltaH = 118.32 kcal` Calculate the `O-H` bond energy in the hydroxyl radical.
Answer» Required equation is `H(g)+O(g)toO-H(g)`, `DeltaH=?` Given, `(1)/(2)H_(2)(g)+(1)/(2)O_(2)(g)toOH(g)," "DeltaH=+10.06kcal` `H(g)to(1)/(2)H_(2)(g)," "DeltaH=-52.09kcal` `O(g)to(1)/(2)O_(2)(g)," "DeltaH=-59.16kcal` Adding, `H(g)+O(g)to OH(g)," "DeltaH=-101.19kcal`

Discussion

204.	The enthalpies of formation of `Al_(2)O_(3)` and `Cr_(2)O_(3)` are `-1596KJ` and `-1134KJ` respectively. `DeltaH` for the reaction `2Al+Cr_(2)O_(2)rarr2Cr+Al_(2)O_(3)` isA. `-1365 kJ`B. `+2730 kJ`C. `-2730 kJ`D. `-462 kJ`
Answer» Correct Answer - D `DeltaH=sumDeltaH_(f)("Products")-sumDeltaH_(f)("reactants")` `=DeltaH_(f)(Al_(2)O_(3))-DeltaH_(f)(Cr_(2)O_(3))` [`DeltaH_(f)` of elements in standard state `=0`] `=-1596 kJ-(-1134 kJ)` `=1134 kJ-1596kJ=-462 kJ`

Discussion

205.	The enthalpies of formation of `Al_(2)O_(3)` and `Cr_(2)O_(3)` are `-1596KJ` and `-1134KJ` respectively. `DeltaH` for the reaction `2Al+Cr_(2)O_(2)rarr2Cr+Al_(2)O_(3)` is
Answer» Correct Answer - `-462kJ`

Discussion

206.	The heat of formation of `CO_(2)` is `-407KJ//mol` . The energy required for the process `3CO_(2)(g)rarr3C(g)+2O_(3)(g)` isA. less than `1221KJ`B. more than `1221KJ`C. is equal to `1221KJ`D. cannot be predicted
Answer» Correct Answer - A `3CO_(2)(g)rarr3C(g)+2O_(3)` `DeltaH=3DeltaH_("atomization" )C(s)rarrC(g))+2Delta_(f)^(@)(O_(3)(g))-3DeltaH_(f)^(@)` `(CO_(2))(g))` `DeltaH=3DeltaH_("atomiztion")C(s)rarrC(g))2DeltaH_(f)^(@)(O_(3)(g))+3xx407` As energy will be required for the processes `C(s)rarrC(g)` and `3O_(2)(g)rarr2O_(3)(g)` `:. DeltaH` will be more than `1221KJ` .

Discussion

207.	Calculate the standard free energy change for the combustion of glucose at 298K, using the given data, `C_(6)H_(12)O_(6)+6O_(2)to6CO_(2)+6H_(2)O` `DeltaH^(@)=-2820kJ" "mol^(-1),DeltaS^@=210JK^(-1)" "mol^(-1)`
Answer» `DeltaG^(@)=-2882.58kJ" "mol^(-1)`

Discussion

208.	The difference between `DeltaH` and `DeltaE` (on a molar basis) for the combustion of n-octane `(l)` at `25^(@)C` would be:A. `-13.6KJ`B. `1.14KJ`C. `-11.15KJ`D. `+11.15KJ`
Answer» Correct Answer - D `C_(8)H_(18)(l)+(25)/(2)O_(2)(g)rarr8CO_(2)(g)+9H_(2)O(l)` `Deltan_(g)=8-(25)/(2)=(16-25)/(2)=-4.5` `DeltaH-DeltaE=Deltan_(g)RT=-(4.5xx8.314xx298)/(1000)=-11.15KJ`

Discussion

209.	For the combustion reaaction at `298K` , `H_(2)(g)+1//2O_(2)(g)rarrH_(2)O(l)` Which of the following alternetive (s) is/are correct ?A. `DeltaH=DeltaE`B. `DeltaH gt DeltaE`C. `DeltaH lt DeltaE`D. `DeltaH` & `DeltaE` have no relation with each other
Answer» Correct Answer - C `Deltan=-1//2-1=-3//2` Since, `Deltanlt0` `:.DeltaH` is `lt DeltaE`

Discussion

210.	The value of enthalpy change `(DeltaH)` for the reaction `C_(2)H_(5)OH(l)+3O_(2)(g)rarr2CO_(2)(g)+3H_(2)O(l)` at `27^(@)C` is `-1366.5KJmol^(-1)` . The value of internal energy change for the above reaction at this tempearature will beA. `-1371.5KJ`B. `-1369.0KJ`C. `-1364.0KJ`D. `-1361.5KJ`
Answer» Correct Answer - B Relation between `DeltaH` (enthalpy change) and `DeltaE` (internal energy change) is `DeltaH=DeltaE+Deltan_(g)RT` where `Deltan_(g)` =(moles of gaseous products)-(moles of gaseous reactants) For the given reaction, `Deltan_(g)=2-3=-1` implies `-1366.v5=DeltaE=-1xx8.314xx10^(-3)xx300` `:. DeltaE=-1364.0KJmol^(-1)`

Discussion

211.	The value of enthalpy change `(DeltaH)` for the reaction `C_(2)H_(5)OH (l)+3O_(2) (g) rarr 2CO_(2) (g) +3H_(2)O (l)` at `27^(@)C` is `-1366.5 kJ mol^(-1)`. The value of internal energy change for the above reactio at this temperature will beA. `-1371.5 kJ`B. `-1369.0 kJ`C. `-1364.0 kJ`D. `-1361.5kJ`
Answer» Correct Answer - C `C_(2)H_(5)OH(l)+3O_(2)(g)to2CO_(2)(g)+3H_(2)O(s)` `Deltan(g)=2-3=1` `DeltaU=DeltaH-Deltan(g)RT=-1366.5 kJ mol^(-1)` `-(-1xx8.314xx10^(-3)xx300kJ mol^(-1))` `=-1366.5+2.4942=-1364 kJ mol^(-1)`

Discussion

212.	At `500K` , for an isobaric pracess. `DeltaS_(system)=-10(KJ)/(molK)` and `DeltaS_(surr)=12(KJ)/(mol K)` Therefore, `DeltaG` for the entire process isA. `-500KJ//mol`B. `-1000KJ//mol`C. `-600KJ//mol`D. `-1100KJ//mol`
Answer» Correct Answer - D `DeltaS_("total")=DeltaS_("system")-(DeltaH)/(T)=2KJ//mol` or `(DeltaH-TDeltaS)/(T)=-2KJ//mol` or `DeltaH-TDeltaS=-2TKJ//mol=-2xx500KJ//mol` `=-1000(KJ)/(mol)`

Discussion

213.	using following data `H_(2)O(l)[373.15K , 1 atm ] to H_(2)O(g)[ 373.15 K , 1 atm], DeltaS_(1) H_(2)O(s) [ 273 .15 K, 1 atm] to H_(2)O(l)[273.15 K,1 atm], DeltaS_(2)` predict which of the following is correct ?A. `DeltaS_(1)=DeltaS_(2)`B. `DeltaS_(1)gtDeltaS_(2)`C. `DeltaS_(1)ltDeltaS_(2)`D. `DeltaS_(1)` may be greater or smaller than `DeltaS_(2)`
Answer» Correct Answer - c Vaporisation of water creates more creates more randomness. Hence , has more entropy.

Discussion

214.	on the basis of thermochemical equation a,b and c, find out which of the algebraic relationships given in option a , to d . Is correct ? a. C(graphite) ` + O_(2)(g) to CO_(2)(g), Delta_(c)H = x kJ mol^(-1)` b. C(graphite) ` + 1/2O_(2)(g) to CO_(2)(g), Delta_(c)H = y kJ mol^(-1)` `Co(g) + 1//2 O_(2)(g) to CO_(2)(g), Delta_(c)H = zkJ mol^(-1)`A. z=x+yB. x= y-zC. x = y +zD. y=2z-x
Answer» Correct Answer - c `C+O_(2)toCO_(2)(g),Delta_(r)H= xKJ mol^(-1) ......(i)` C (graphite) `+1/2O_(2)(g)to CO(g),Delta_(r)H= y KJ mol^(-1).....(ii)` `CO(g)+1/2O_(2)(g)toCO_(2)(g),Delta_(r)H=z kJ mol^(-1) ...... (iii)` ltbr gt `(i)=(ii)+(iii)` x=y+z

Discussion

215.	Which of the following is nor correct ?A. Dissolution of `NH_(4)Cl` in excess of water is an endothermic processB. Neutralisation is always exothermicC. The absolute value of enthalpy `(H)` can be determined experimentallyD. The heat of reaction ar constant volume is denoted by `DeltaE`
Answer» Correct Answer - C Factual questions.

Discussion

216.	Which of the following are not state functions? (I) `q+w` (II)`q` (III) `w` (IV) `H-TS`A. `I` and `IV`B. `II`, `III` and `IV`C. `I`, `II` and `III`D. `II` and `III`
Answer» Correct Answer - D `q` and `w` are not state functions.

Discussion

217.	Assertion:Spontaneous process is an irreversible process and may be reversed by some external agency. Reason:Decrease in enthalpy is a conrtributory factor for spontaneity.A. If both ther assertion and reason are true and the reason is the correct explanation of the assertion.B. If both the assertion and reason are true but reason is not the correct explantion of the assertion.C. If the assertion is true but reason is false.D. If assertion is false but reason is true.
Answer» Correct Answer - A Both are separate fects.

Discussion

218.	The internal energy change when a system goes fromk state `A` to `B` is `40 kJ mol^(-1)`. If the system goes from `A` to `B` by a reversible path and returns to state `A` by an irreversible path, what would be the net change in internal energy?A. `40 kJ`B. ` gt 40 kJ`C. ` lt 40 kJ`D. zero
Answer» Correct Answer - D Change in internal energy is a state function `:. DeltaU(AtoB)=40 kJ mol^(-1)` `DeltaU(BtoA)=-40 kJ mol^(-1)` `:. ` Net change in internal energy `=` Zero.

Discussion

219.	A reaction occurs spontaneously if:A. `TDeltaS lt DeltaH` and both `DeltaH` and `DeltaS` are `+ve`B. `TDeltaS gt DeltaH` and both `DeltaH` and `DeltaS` are `+ve`C. `TDeltaS = DeltaH` and both `DeltaH` and `DeltaS` are `+ve`D. `TDeltaS lt DeltaH` and `DeltaH` is `+ve` and `DeltaS` is `-ve`
Answer» Correct Answer - B `DeltaG=DeltaH-TDeltaS` When both `DeltaH` and `DeltaS` are `+ve`, for reaction to be spontaneous `(DeltaG lt0)`, `TDeltaS gt DeltaH` (When `DeltaH` is `+ve` and `DeltaS` is `-ve`, the reaction in never spontaneous)

Discussion

220.	The absolute enthalpy of neutralization of the reaction, `MgO(s)+2HCl(aq.)+H_(2)O(l)` will beA. `-57.33` kJ `mol^(-1)`B. greater than -57.33 kJ `mol^(-1)`C. less than -57.33 kJ `mol^(-1)`D. 57.33 kJ `mol^(-1)`
Answer» Correct Answer - C Since MgO is an oxide of a weak base, hence its neutralisation will evolve the heat less than 57.33 kJ `mol^(-1)`

Discussion

221.	The absolute enthalpy of neutralization of the reaction, `MgO(s)+2HCl(aq.)+H_(2)O(l)` will beA. less than `-57.33 kJ mol^(-1)`B. `-57.33 kJ mol^(-1)`C. greater than `-57.33 kJ mol^(-1)`D. `57.33 kJ mol^(-1)`
Answer» Correct Answer - C The absolute value of enthalpy of neutralisation of this reaction is greater than `-57.33 kJ mol^(-1)` . This is due to very high enthalpy of hydration of `Mg^(2+)` ion. Infact the `DeltaH` for this reaction is nearly `-146 kJ`. Thus enthalpy of neutralisation per mole of `H^(+) ion` is nearly`-73 kJ`, which is greater than enthalpy of neutralisation of strong acid `V_(s)` strong base i.e., `-57.33 kJ`.

Discussion

222.	The value of `DeltaH_(O-H)` is `109Kcal//mol` . The enthalpy of formation of 1 mole of water in gaseous state will beA. `109xx2KJmol^(-1)`B. `109KJmol^(-1)`C. data is not sufficient to predict itD. `109xx4Kcalmol^(-1)`
Answer» Correct Answer - B Formation of water does not merely require the formation of two `O-H` bonds but also require the dissociation of `1mol` of `H_(2)` and `(1)/(2)mol` of `O_(2)` `H_(2)(g)+(1)/(2)O_(2)(g)rarrH_(2)O(g)`

Discussion

223.	Find bond enthalpy of S-S bond from the following data: `C_(2)H_(5)-S-C_(2)H_(5)," "DeltaH_(f)^(@)=-147.2kJ" "mol^(-1)` `C_(2)H_(5)-S-S-C_(2)H_(5)," "DeltaH_(f)^(@)=-201.9kJ" "mol^(-1)` `S(g)," "DeltaH_(f)^(@)=222.8kJ" "mol^(-1)`
Answer» `4C(s)+5H_(2)O+StoH-underset(H)underset(\|)overset(H)overset(\|)(C)-underset(H)underset(\|)overset(H)overset(\|)(C)-S-underset(H)underset(\|)overset(H)overset(\|)(C)-underset(H)underset(\|)overset(H)overset(\|)(C)-H` `4C(s)+5H_(2)+2StoH-underset(H)underset(\|)overset(H)overset(\|)(C)-underset(H)underset(\|)overset(H)overset(\|)(C)-S-S-underset(H)underset(\|)overset(H)overset(\|)(C)-underset(H)underset(\|)overset(H)overset(\|)(C)-H` `DeltaH=sum(BE)_(R)-sum(BE)_(P)` (i). `-147.2="Heat of atomization of 4C, 10H, 1S"` `-BE" of "10(C-H),2(C-s),2(C-C)` (ii) `-201.9="Heat of atomization of 4C",10H,2S` `-BE` of `10(C-H),2(C-S),2(C-C),(S-S)` Subtracting (i) from (ii), `-201.9+147.2="Heat of atomization of "1S-BE" of "(S-S)` `=222.8kJ-BE` of `(S-S)` BE of `(S-S)=277.5kJ`

Discussion

224.	(1) For the given heat of reaciton, (i) `C(s)+O_(2)(g)=CO_(2)(g)+97 kcal` (ii) `CO_(2)(g)+C(s)=2CO(g)-39 kcal` the heat of combustion of `CO(g)` is:A. `68Kcal`B. `-68Kcal`C. `+48Kcal`D. None
Answer» Correct Answer - A Subtracting equattion (ii) from equation (i), we get `C(s)+O_(2)(g)=CO_(2)(g)+97Kcal` `(CO_(2)(g)+C(s)=2CO(g)-39Kcal)/(or -CO_(2)(g)+O_(2)(g)-2CO(g)+136Kcal)` or, `2CO(g)+O_(2)=CO_(2)(g)+136Kcal` or, `CO(g)+1//2O_(2)(g)=CO_(2)(g)68Kcal` Required value `=68Kcal`

Discussion

225.	Oxidising power of chlorine in aqueous solution can be determined by the parameters indicated below `(1)/(2)CL_(2)(g)overset((1)/(2)Delta_(diss)H^(Theta))(rarr)Cl(g)overset(DeltaH_(Eg)^(Theta))(rarr)` `Cl^(-)(g)overset(Delta_(hyd)H^(Theta))(rarr)Cl^(-)(aq)` The energy involved in the conversion of `(1)/(2)Cl_(2)(g)` to `Cl^(-)(aq)` (Using the data `Delta_(diss)H_(Cl_(2))^(Theta)=240KJ mol^(-1)`) `Delta_(Eg)H_(Cl)^(Theta)=-349KJmol^(-1)` , `Delta_(Eg)H_(Cl)^(Theta)=-381KJmol^(-1)`) will beA. `+152c `B. `-610KJmol^(-1)`C. `-850KJmol^(-1)`D. `+120KJmol^(-1)`
Answer» Correct Answer - D `(1)/(2)Cl_(2)(g)rarrCl^(-)(aq)` `DeltaH=(1)/(2)DeltaH_(diss)(Cl_(2))+DeltaH_(EA)Cl+DeltaH_(hyd)(Cl^(-))` `=(240)/(2)-349-381=-610KJmol^(-1)`

Discussion

226.	Enthalpy of combustion of `CH_(4)` , `C_(2)H_(6)` and `C_(3)H_(8)` are `-210-370` and `-530Kcal//mol` respectivaly. The approximate value of enthalpy of combustion of `n`-hexane isA. `-1170 (Kcal)/(mol)`B. `-750(Kcal)/(mol)`C. `-1010(Kcal)/(mol)`D. `-590(Kcal)/(mol)`
Answer» Correct Answer - A For each `-CH_(2)` the enthaply of combustion is increased by `160Kcal//mol` . `:. Delta_(comb)H(C_(6)H_(6))-210-5xx160=-1010(Kcal)/(mol)`

Discussion

227.	When reaction is at standard state at equilibrium, thenA. `DeltaH^(@)=0`B. `DeltaS^(@)=0`C. equilibrium constant `K=0`D. equilibrium constant `K=1`
Answer» Correct Answer - B Equilibrium at standard state means equilibrium constant is 1.

Discussion

228.	Equal volumes of molar hydrochloric acid and subphuric acid are neutralized by dil. `NaOH` solution and `x` Kcal and `y` Kcal of heat are liberated respectively. Which of the following is true?A. `x=y`B. `x=(1)/(2)y`C. `x=2y`D. None of these
Answer» Correct Answer - A 1 `MH_(2)SO_(4)=2 " geq"` of `H_(2)SO_(4)` Hence, `y=2x` or `x=(1)/(2)y`

Discussion

229.	Which statements among the following is /are incorrect ?A. Absoulte value of heat content of the system can be easily determined by calorimetery.B. Absoulte value of entropy cannot be knownC. Absolute value of internal energy cannot be knownD. Value of `DeltaG_(f)^(@)` cannot be determined.
Answer» Correct Answer - A::D The statements `(A)` and `(D)` are incorrect. `DeltaG_(f)^(@)` can be determined where absolute value of heat content cannot be determined.

Discussion

230.	In which process net work done is zero ?A. CyclicB. IsochoricC. Free expansionD. Adiabatic
Answer» Correct Answer - C `W=-P_(ext)DeltaV` For free expansion `P_(ext)=0` `:. W=0` .

Discussion

231.	Identify the correct statement regarding a spontaneous process.A. Lowering of energy in the reaction process is the only criterion for spontaneityB. For a spontaneous process in an isolated system ,the change in entropy is positiveC. Endothermic reaction are never spontaneousD. Exothermic reactions are always spontaneous.
Answer» Correct Answer - B For a spontaneous process, `DeltaS_("total")` is `+ve`

Discussion

232.	In which cases of maxing of a strong acid and a base each of `1N` concentration, increases in temperature is the highest.A. `20ml` acid `-30ml` alkaliB. `10ml` acid `-40ml` alkaliC. `25ml` acid `-25ml` alkaliD. `35ml` acid `-15ml` alkali
Answer» Correct Answer - B Assertion and reason show that reaction at equilibrium state in which `DeltaG=0,DeltaS=0` .

Discussion

233.	Enthalpy of combustion of `C_(6) H_(6) (l)` is - 3264. 64 kj/ mol . The heat produced by burning 3. 9 g of benzene isA. `-163.23 kJ`B. `` 326 . 4 kJC. ` 32.64 kJ`D. `-3.254 kJ`
Answer» Correct Answer - a since , heat evolved when 78 g benzene is burnt `=-3264.6 kJ` therefore, heat produced , by buring 3.9 g benzence `3.9/78xx(-3264.6)=-163.23 kJ`

Discussion

234.	A molecule with highest bond energy isA. `Br_(4)`B. `F_(2)`C. `cl_(2)`D. `l_(2)`
Answer» Correct Answer - c the bond energy of `Cl_(2)` is the highest among the given.

Discussion

235.	Which of the following are not state functions? (I) `q+w` (II)`q` (III) `w` (IV) `H-TS`A. `(II),(III)` and `(IV)`B. `(I),(II)` and `(III)`C. `(II)` and `(III)`D. ``(I)` and `(IV)`
Answer» Correct Answer - A `E` and `G(H-TS)` are state functions. Also, `DeltaE=q+w` is a state function. But `q` and `w` are path dependent and not state function.

Discussion

236.	In order to decompose 9 grams of water 142.5 KJ heat is required. Hence the enthalpy of formation of water isA. `-142.5 kJ`B. `+142.5 kJ`C. `-285 kJ`D. `+285 kJ`
Answer» Correct Answer - C Heat required to decompose `1` mol `(18)g` of `H_(2)O=2xx142.5=285kJ` `DeltaH_(f)` is the reverse of heat required `=285 kJ mol^(-1)`

Discussion

237.	In which of the following reactions,standard reaction entropy change`(DeltaS^(@))`is positive and standard Gibb,s energy change`(DeltaG^(@))`decreases sharply with increasing temperature?A. `Mg(s)+(1)/(2)O_(2)(g)rarrMgO(s)`B. `(1)/(2)C("graphite")+(1)/(2)O_(2)(g)rarr(1)/(2)CO_(2)(g)`C. `C("graphite")+(1)/(2)O_(2)(g)rarrCO(g)`D. `CO(g)+(1)/(2)O_(2)(g)rarrCO_(2)(g)`
Answer» Correct Answer - A `C(s)+(1)/(2)O_(2)(g)rarrCO(g),Deltan+(1)/(2)` . Also the moles of gases increase and therefore entropy change `(DeltaS)` is positive. An increase in temperature will causes more change in `TDeltaS` . Also it is a combustion reaction and thus `DeltaH=-ve` Since `DeltaG=DeltaH-TDeltaS` `=-ve-(+ve)=-ve`

Discussion

238.	For the combustion of n-octane `C_(8)H_(18)+O_(2)rarrCO_(2)+H_(2)O` at `25^(@)C` (ingnoring resonance in `CO_(2)`)A. `DeltaH=DeltaE-5.5xx8.31xx0.298 in KJ//mol`B. `DeltaH=DeltaE-4.5xx8.31xx0.298 in KJ//mol`C. `DeltaH=DeltaE-4.5xx8.31xx0.298 in KJ//mol`D. `DeltaH=DeltaE-4.5xx8.31xx0.298 in KJ//mol`
Answer» Correct Answer - D `C_(8)H_(18(l))+12.5O_(2(g))rarr8CO_(2(g))+9H_(2)O_(l)` `DeltaH=DeltaE+(8-12.5)xx8.31xx0.298` in `KJ//mol`

Discussion

239.	Bond dissociation energy of`CH_(3)-H`bond is`103Kcalmol^(-1)`and`0.055cal//g ` respectively ,If specific heat of iodine is `24cal//g` at `200^(@)`,Calcualte its value at`250^(@)C` isA. `3.61Kcalmol^(-1)`B. `-3.61Kcalmol^(-1)`C. `33.61Kcalmol^(-1)`D. `-33.61Kcalmol^(-1)`
Answer» Correct Answer - C `CH_(4)(g)=CH_(3)(g)+H("atom,g")` `(DeltaH_(f))_(CH_(3),H)CH_(3)-H=103` `=DeltaH_(f)(CH_(3),g)+DeltaH_(f)(H "atom, g")-DeltaH_(f)(CH_(4),g)` `(DeltaH_(f))_(CH_(3)g)=103-(103)/(2)+(-17.889)=33.611Kcalmol^(-1)` `:.` Heat of formation of methyl radical is `DeltaH=33.611Kcalmol^(-1)`

Discussion

240.	Given,`H_(s)(g)=2H(g)Delta_(H-H)=103kcalmol^(-1)` `CH_(4)(g)=CH_(3)(g)+H(g)Delta_(CH_(3)-H)=103kcalmol^(-1)` The heat of reaction of `CH_(4)(g) = CH_(3)(g) + H(g)`A. `103Kcalmol^(-1)`B. `206Kcalmol^(-1)`C. 51.5D. zero
Answer» Correct Answer - C `CH_(4)(g)=CH_(3)(g)+H(g)` `D_(CH_(3-H))=103"Kcalmol"^(-1)` `H(g)+H(g)=H_(2)(g)` `(D_(H-H)=-103Kcalmol^(-1))/(Ch_(4)(g)+H(g)=CH_(4)(g)+H_(2)(g))` `DeltaH=103-103=0`

Discussion

241.	The standard enthalpy of formation of `NH_(3)` is `-46.0KJ mol^(-1)` . If the enthalpy of formation of `H_(2)` from its atoms is `-436KJ mol^(-1)` and that of `N_(2)` is `-712KJ mol^(-1)` , the average bond enthalpy of `N-H` bond in `NH_(3)` isA. `-1102 kJ mol^(-1)`B. `-964 kJ mol^(-1)`C. `-352 kJ mol^(-1)`D. `+1056 kJ mol^(-1)`
Answer» Correct Answer - C `(1)/(2)N_(2)(g)+(3)/(2)H_(2)(g)toNH_(3)(g)` `DeltaH_(f)^(@)=-46.0 kJ mol^(-1)` `2H(g)toH_(2)(g)`, `DeltaH_(f)^(@)=-436 kJ mol^(-1)` `2N(g)toN_(2)(g)` , `DeltaH_(f)^(@)=-712 kJ mol^(-1)` Assuming `x` as the bond energy of `N-H` bond (in `kJ mol^(-1)`) `(1)/(2)xx(-712)+(3)/(2)xx(-436)-3x=-46.0` `:. 3x=1056 kJ mol^(-1)` `x=352 kJ mol^(-1)`

Discussion

242.	Given `H_(2)(g)=2H(g)Delta_(H-H)=103Kcal mol^(-1)` The heat of reaction of `CH_(4)(g)=CH_(3)(g)+H(g)`A. `103Kcalmol^(-1)`B. `206Kcalmol^(-1)`C. `51.5Kcalmol^(-1)`D. zero
Answer» Correct Answer - B `CH_(4)(g)=CH_(3)(g)+H(g) " "…(1)` `Delta_(CH_(3)-H)=103Kcalmol^(-1)` `H(g)+H(g)=H_(2)(g)" "…(2)` `(Delta_(H-H)=-103Kcalmol^(-1))/(CH_(4)(g)+H(g)=CH_(4)(g)+H_(2)(g),DeltaH=103-103=0)`

Discussion

243.	The reaction of cyanamide `NH_(2)CN(s)` with oxygen was carries out in a bomb calorimeter and `Deltaq_(v)` at `300K` was measured to be `-750KJ//mol` . The value of `DeltaH` per mole of `NH_(2)CN(s)` in the given reaction isA. `-741.75KJ//mol`B. `-748.75KJ//mol`C. `-752.75KJ//mol`D. `-750KJ//mol`
Answer» Correct Answer - A The combustion reaction is: `NH_(2)CN(s)+(3)/(2)O_(2)(g)rarrN_(2)(g)+CO_(2)(g)+H_(2)O(l)` `Deltan=(1)/(2)` `DeltaH=DeltaE+DeltanRT=-750+(1)/(2)xx8.314xx10^(-3)xx300` or `DeltaH=-750+0.15xx8.314=-748.75KJ//mol`

Discussion

244.	When 1 mole of gas is heated at constant volume. Temperature is raised from `298` to `308K` . Heat supplied to the gas is `500J` . Then which stamenet is correct?A. `q=-W=500J,DeltaU=0`B. `q=DeltaU=500J,W=0`C. `q=-W=500J,DeltaU=0`D. `DeltaU=0,q=W=-500J`
Answer» Correct Answer - C We Know that, `DeltaH=DeltaE+PDeltaV` When, `DeltaV=0` , `:. DeltaH=DeltaE` From the first law of thermodynamics, `DeltaE=q-W` In the given problem,`DeltaH=500J` `-W=- PDeltaV,DeltaV=0` So, `DeltaE=q=500J`

Discussion

245.	When 1 mole of gas is heated at constant volume. Temperature is raised from `298` to `308K` . Heat supplied to the gas is `500J` . Then which stamenet is correct?A. `q=W=500 J`, `DeltaU=0`B. `q=DeltaU=500 J`, `W=0`C. `q=W=500 J`, `DeltaU=500`D. `DeltaU=0`, `q=W=-500 J`
Answer» Correct Answer - B As volume is constant, `W=0` ` :. DeltaV=+500J=q`

Discussion

246.	If for a given substance, melting point is `T_(B)` and freezing point is `T_(A)` then correct variation of entropy is by graph between entropy change and temperature isA. B. C. D.
Answer» Correct Answer - A For a pure substance `T_(A)` and `T_(B)` represent the same temperature. Hence `A` is a correct choice.

Discussion

247.	Which of the following conditions regarding the chemical process ensures its sponteneity at all temperaturesA. `DeltaH lt0` , `DeltaS lt 0`B. `DeltaH gt0` , `DeltaS lt 0`C. `DeltaH lt0` , `DeltaS gt 0`D. `DeltaH gt0` , `DeltaS gt 0`
Answer» Correct Answer - C `DeltaH lt 0` , `DeltaS gt0` are always favourable conditions at all temperatures.

Discussion

248.	Which of the following are state functions? (i) Q (ii) w (iii). Q+w (iv) Q-w (v) `Q_v` (vi) `Q_(pP)` (vii) `(Q)/(w)` (viii). `(Q)/(T)` (ix) `(DeltaX)/(T)` (x) `U+PV` (xi) `U-PV`
Answer» (iv),(v),(vi),(viii),(ix),(x)

Discussion

249.	In the adjoining diagram, the p-V graph of an ideal gas is shown. Find out from the graph (i) work done in taking the gas From the state `AtoB` (ii) Work done in taking the gas from `BtoC` (iii) Work done in a complete cycle. (1 litre`=10^(-3)m^(3)`)
Answer» (i) `-60xx10^(2)J` (ii) zero (iii) `36xx10^(2)J` , i.e., net work is done by the gas

Discussion

250.	When reaction is at standard state at equilibrium, thenA. `80%`B. `87%`C. `90%`D. `97%`
Answer» Correct Answer - B Precentage efficiency of the fuel cell `=(DeltaG)/(DeltaH)xx100` . The concerned reaction is `CH_(3)OH(l)+(3)/(2)O_(2)(g)rarrCO_(2)+2H_(2)O(l)` `DeltaG_(r)[DeltaG_(f)(CO_(2),g)+2DeltaG_(f)(H_(2)O,l)]` `[-DeltaG_(f)(CH_(3)OH,l)-(3)/(2)DeltaG_(f)(O_(2),g)]` `=-394.4+2(-237.2)-(-166.2)-0` `=-394.4-474.4+166.2=-702.6KJmol^(-1)` Percentage effieiency `=(702.6)/(762)xx100=96.78%=97%`

Discussion

Explore topic-wise InterviewSolutions in .

Calculate the enthalpy change for the following reaction: `CH_(4)(g)+2O_(2)(g)toCO_(2)(g)+2H_(2)O(l)` given, enthalpies of formation of `CH_(4),CO_(2) and H_(2)O` are `-74.8kJ` `mol^(-1),-393.5kJ" "mol^(-1) and -286.2kJ" "ml^(-1)` respectively.

The enthalpies of formation of `Al_(2)O_(3)` and `Cr_(2)O_(3)` are `-1596KJ` and `-1134KJ` respectively. `DeltaH` for the reaction `2Al+Cr_(2)O_(2)rarr2Cr+Al_(2)O_(3)` isA. `-2730KJ`B. `-462KJ`C. `-1365KJ`D. `+2730KJ`

The enthalpies of formation of `Al_(2)O_(3)` and `Cr_(2)O_(3)` are `-1596KJ` and `-1134KJ` respectively. `DeltaH` for the reaction `2Al+Cr_(2)O_(2)rarr2Cr+Al_(2)O_(3)` isA. `-1365 kJ`B. `+2730 kJ`C. `-2730 kJ`D. `-462 kJ`

The enthalpies of formation of `Al_(2)O_(3)` and `Cr_(2)O_(3)` are `-1596KJ` and `-1134KJ` respectively. `DeltaH` for the reaction `2Al+Cr_(2)O_(2)rarr2Cr+Al_(2)O_(3)` is

The heat of formation of `CO_(2)` is `-407KJ//mol` . The energy required for the process `3CO_(2)(g)rarr3C(g)+2O_(3)(g)` isA. less than `1221KJ`B. more than `1221KJ`C. is equal to `1221KJ`D. cannot be predicted

Calculate the standard free energy change for the combustion of glucose at 298K, using the given data, `C_(6)H_(12)O_(6)+6O_(2)to6CO_(2)+6H_(2)O` `DeltaH^(@)=-2820kJ" "mol^(-1),DeltaS^@=210JK^(-1)" "mol^(-1)`

The difference between `DeltaH` and `DeltaE` (on a molar basis) for the combustion of n-octane `(l)` at `25^(@)C` would be:A. `-13.6KJ`B. `1.14KJ`C. `-11.15KJ`D. `+11.15KJ`

For the combustion reaaction at `298K` , `H_(2)(g)+1//2O_(2)(g)rarrH_(2)O(l)` Which of the following alternetive (s) is/are correct ?A. `DeltaH=DeltaE`B. `DeltaH gt DeltaE`C. `DeltaH lt DeltaE`D. `DeltaH` & `DeltaE` have no relation with each other

The value of enthalpy change `(DeltaH)` for the reaction `C_(2)H_(5)OH(l)+3O_(2)(g)rarr2CO_(2)(g)+3H_(2)O(l)` at `27^(@)C` is `-1366.5KJmol^(-1)` . The value of internal energy change for the above reaction at this tempearature will beA. `-1371.5KJ`B. `-1369.0KJ`C. `-1364.0KJ`D. `-1361.5KJ`

At `500K` , for an isobaric pracess. `DeltaS_(system)=-10(KJ)/(molK)` and `DeltaS_(surr)=12(KJ)/(mol K)` Therefore, `DeltaG` for the entire process isA. `-500KJ//mol`B. `-1000KJ//mol`C. `-600KJ//mol`D. `-1100KJ//mol`

Which of the following is nor correct ?A. Dissolution of `NH_(4)Cl` in excess of water is an endothermic processB. Neutralisation is always exothermicC. The absolute value of enthalpy `(H)` can be determined experimentallyD. The heat of reaction ar constant volume is denoted by `DeltaE`

Which of the following are not state functions? (I) `q+w` (II)`q` (III) `w` (IV) `H-TS`A. `I` and `IV`B. `II`, `III` and `IV`C. `I`, `II` and `III`D. `II` and `III`

The internal energy change when a system goes fromk state `A` to `B` is `40 kJ mol^(-1)`. If the system goes from `A` to `B` by a reversible path and returns to state `A` by an irreversible path, what would be the net change in internal energy?A. `40 kJ`B. ` gt 40 kJ`C. ` lt 40 kJ`D. zero

A reaction occurs spontaneously if:A. `TDeltaS lt DeltaH` and both `DeltaH` and `DeltaS` are `+ve`B. `TDeltaS gt DeltaH` and both `DeltaH` and `DeltaS` are `+ve`C. `TDeltaS = DeltaH` and both `DeltaH` and `DeltaS` are `+ve`D. `TDeltaS lt DeltaH` and `DeltaH` is `+ve` and `DeltaS` is `-ve`

The absolute enthalpy of neutralization of the reaction, `MgO(s)+2HCl(aq.)+H_(2)O(l)` will beA. `-57.33` kJ `mol^(-1)`B. greater than -57.33 kJ `mol^(-1)`C. less than -57.33 kJ `mol^(-1)`D. 57.33 kJ `mol^(-1)`

The absolute enthalpy of neutralization of the reaction, `MgO(s)+2HCl(aq.)+H_(2)O(l)` will beA. less than `-57.33 kJ mol^(-1)`B. `-57.33 kJ mol^(-1)`C. greater than `-57.33 kJ mol^(-1)`D. `57.33 kJ mol^(-1)`

The value of `DeltaH_(O-H)` is `109Kcal//mol` . The enthalpy of formation of 1 mole of water in gaseous state will beA. `109xx2KJmol^(-1)`B. `109KJmol^(-1)`C. data is not sufficient to predict itD. `109xx4Kcalmol^(-1)`

Find bond enthalpy of S-S bond from the following data: `C_(2)H_(5)-S-C_(2)H_(5)," "DeltaH_(f)^(@)=-147.2kJ" "mol^(-1)` `C_(2)H_(5)-S-S-C_(2)H_(5)," "DeltaH_(f)^(@)=-201.9kJ" "mol^(-1)` `S(g)," "DeltaH_(f)^(@)=222.8kJ" "mol^(-1)`

(1) For the given heat of reaciton, (i) `C(s)+O_(2)(g)=CO_(2)(g)+97 kcal` (ii) `CO_(2)(g)+C(s)=2CO(g)-39 kcal` the heat of combustion of `CO(g)` is:A. `68Kcal`B. `-68Kcal`C. `+48Kcal`D. None

Enthalpy of combustion of `CH_(4)` , `C_(2)H_(6)` and `C_(3)H_(8)` are `-210-370` and `-530Kcal//mol` respectivaly. The approximate value of enthalpy of combustion of `n`-hexane isA. `-1170 (Kcal)/(mol)`B. `-750(Kcal)/(mol)`C. `-1010(Kcal)/(mol)`D. `-590(Kcal)/(mol)`

When reaction is at standard state at equilibrium, thenA. `DeltaH^(@)=0`B. `DeltaS^(@)=0`C. equilibrium constant `K=0`D. equilibrium constant `K=1`

Equal volumes of molar hydrochloric acid and subphuric acid are neutralized by dil. `NaOH` solution and `x` Kcal and `y` Kcal of heat are liberated respectively. Which of the following is true?A. `x=y`B. `x=(1)/(2)y`C. `x=2y`D. None of these

Which statements among the following is /are incorrect ?A. Absoulte value of heat content of the system can be easily determined by calorimetery.B. Absoulte value of entropy cannot be knownC. Absolute value of internal energy cannot be knownD. Value of `DeltaG_(f)^(@)` cannot be determined.

In which process net work done is zero ?A. CyclicB. IsochoricC. Free expansionD. Adiabatic

In which cases of maxing of a strong acid and a base each of `1N` concentration, increases in temperature is the highest.A. `20ml` acid `-30ml` alkaliB. `10ml` acid `-40ml` alkaliC. `25ml` acid `-25ml` alkaliD. `35ml` acid `-15ml` alkali

Enthalpy of combustion of `C_(6) H_(6) (l)` is - 3264. 64 kj/ mol . The heat produced by burning 3. 9 g of benzene isA. `-163.23 kJ`B. `` 326 . 4 kJC. ` 32.64 kJ`D. `-3.254 kJ`

A molecule with highest bond energy isA. `Br_(4)`B. `F_(2)`C. `cl_(2)`D. `l_(2)`

Which of the following are not state functions? (I) `q+w` (II)`q` (III) `w` (IV) `H-TS`A. `(II),(III)` and `(IV)`B. `(I),(II)` and `(III)`C. `(II)` and `(III)`D. ``(I)` and `(IV)`

In order to decompose 9 grams of water 142.5 KJ heat is required. Hence the enthalpy of formation of water isA. `-142.5 kJ`B. `+142.5 kJ`C. `-285 kJ`D. `+285 kJ`

For the combustion of n-octane `C_(8)H_(18)+O_(2)rarrCO_(2)+H_(2)O` at `25^(@)C` (ingnoring resonance in `CO_(2)`)A. `DeltaH=DeltaE-5.5xx8.31xx0.298 in KJ//mol`B. `DeltaH=DeltaE-4.5xx8.31xx0.298 in KJ//mol`C. `DeltaH=DeltaE-4.5xx8.31xx0.298 in KJ//mol`D. `DeltaH=DeltaE-4.5xx8.31xx0.298 in KJ//mol`

Bond dissociation energy of`CH_(3)-H`bond is`103Kcalmol^(-1)`and`0.055cal//g ` respectively ,If specific heat of iodine is `24cal//g` at `200^(@)`,Calcualte its value at`250^(@)C` isA. `3.61Kcalmol^(-1)`B. `-3.61Kcalmol^(-1)`C. `33.61Kcalmol^(-1)`D. `-33.61Kcalmol^(-1)`

Given,`H_(s)(g)=2H(g)Delta_(H-H)=103kcalmol^(-1)` `CH_(4)(g)=CH_(3)(g)+H(g)Delta_(CH_(3)-H)=103kcalmol^(-1)` The heat of reaction of `CH_(4)(g) = CH_(3)(g) + H(g)`A. `103Kcalmol^(-1)`B. `206Kcalmol^(-1)`C. 51.5D. zero

Given `H_(2)(g)=2H(g)Delta_(H-H)=103Kcal mol^(-1)` The heat of reaction of `CH_(4)(g)=CH_(3)(g)+H(g)`A. `103Kcalmol^(-1)`B. `206Kcalmol^(-1)`C. `51.5Kcalmol^(-1)`D. zero

The reaction of cyanamide `NH_(2)CN(s)` with oxygen was carries out in a bomb calorimeter and `Deltaq_(v)` at `300K` was measured to be `-750KJ//mol` . The value of `DeltaH` per mole of `NH_(2)CN(s)` in the given reaction isA. `-741.75KJ//mol`B. `-748.75KJ//mol`C. `-752.75KJ//mol`D. `-750KJ//mol`

When 1 mole of gas is heated at constant volume. Temperature is raised from `298` to `308K` . Heat supplied to the gas is `500J` . Then which stamenet is correct?A. `q=-W=500J,DeltaU=0`B. `q=DeltaU=500J,W=0`C. `q=-W=500J,DeltaU=0`D. `DeltaU=0,q=W=-500J`

When 1 mole of gas is heated at constant volume. Temperature is raised from `298` to `308K` . Heat supplied to the gas is `500J` . Then which stamenet is correct?A. `q=W=500 J`, `DeltaU=0`B. `q=DeltaU=500 J`, `W=0`C. `q=W=500 J`, `DeltaU=500`D. `DeltaU=0`, `q=W=-500 J`

If for a given substance, melting point is `T_(B)` and freezing point is `T_(A)` then correct variation of entropy is by graph between entropy change and temperature isA. B. C. D.

Which of the following conditions regarding the chemical process ensures its sponteneity at all temperaturesA. `DeltaH lt0` , `DeltaS lt 0`B. `DeltaH gt0` , `DeltaS lt 0`C. `DeltaH lt0` , `DeltaS gt 0`D. `DeltaH gt0` , `DeltaS gt 0`

Which of the following are state functions? (i) Q (ii) w (iii). Q+w (iv) Q-w (v) `Q_v` (vi) `Q_(pP)` (vii) `(Q)/(w)` (viii). `(Q)/(T)` (ix) `(DeltaX)/(T)` (x) `U+PV` (xi) `U-PV`

In the adjoining diagram, the p-V graph of an ideal gas is shown. Find out from the graph (i) work done in taking the gas From the state `AtoB` (ii) Work done in taking the gas from `BtoC` (iii) Work done in a complete cycle. (1 litre`=10^(-3)m^(3)`)

When reaction is at standard state at equilibrium, thenA. `80%`B. `87%`C. `90%`D. `97%`