Thermo Chemistry.pdf

452 Thermodynamics and Thermochemistry

1.

The internal energy change when a system goes from state A to B is 40 kJ/mole. 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

8.

(a) 2 Joule

(b) 4 Joule

(c) Zero

(d) Infinite

Heat exchanged in a chemical reaction at constant temperature and constant pressure is called as

[CBSE PMT 2003]

2.

3.

(a) 40 kJ

(b) > 0 kJ

(c) < 40 kJ

(d) Zero

The correct relationship is

[DPMT 2002]

(a) H  PV  V

(b) H  nRT  E

(c) E  nRT  P

(d) None of these

For

CaCO 3 (s) ⇌ CaO(s)  CO2 (g)

9.

(b) 186.4 kJ

(c) 165.6 kJ

(d) 160 kJ

Values of H and S for five different reactions are given below. Reaction

H (kJ mol 1 )

S ( JK 1 mol 1 )

I

+98.0

+14.8

II

– 55.5

–84.6

III

+28.3

–17.0

IV

– 40.5

+24.6

V

+ 34.7

0.0

10.

Which of the following statements is true[KCET 2002]

(a) Reaction I

(b) Reaction II

(c) Reaction III

(d) Reaction IV

(a) First law of thermodynamics (b) Law of conservation of energy (c) Law of conservation of mass (d) Modified form of Ist law of thermodynamics 11.

Molar heat capacity of water in equilibrium with ice at constant pressure is [IIT JEE 1997] (a) Zero

(b) Infinity ()

(c) 40 .45 kJ K 1 mol 1

(d) 75 . 48 J K 1

Mass and energy are conserved is demonstrated by [MH CET 2002]

(e) Reaction V

12.

The enthalpy of the reaction, H 2 (g ) 

1 O 2 (g)  H 2 O(g) is H 1 and that of 2

H 2 (g ) 

1 O 2 (g)  H 2 O(l) is H 2 . Then 2

[KCET 2004]

(a) H 1  H 2

(b) H1  H 2  0

(c) H 1  H 2

(d) H 1  H 2

A reaction occurs spontaneously if [MP PET 2002; CBSE PMT 2005]

Internal energy does not include

(a) TS  H and both H and S are +ve

[AIIMS 1999; CPMT 2000]

(a) Nuclear energy

(b) TS  H and both H and S are +ve

(b) Rotational energy

(c) TS  H and both H and S are +ve

(c) Vibrational energy

(d) TS  H and H is +ve and S is –ve

(d) Energy arising by gravitational pull 7.

(d) Free energy

(c) E may be lesser or greater or equal to H

[Kerala PMT 2004; KCET 1988,90]

6.

(c) Entropy

(d) E is always proportional to H

On the basis of these values predict which one of these will be spontaneous at all tempeature

5.

(b) Enthalpy

(b) E is always less than H

[BVP 2003]

(a) 180 kJ

(a) Internal energy

(a) E is always greater than H

977 o C ;

at

H  176 kJ mol, then E is

4.

[BHU 1998; Pb. PET 2000; MP PET 2002]

Two moles of an ideal gas expand spontaneously into a vacuum. The work done is [AMU 2000]

13.

Which expression is correct for the work done in adiabatic reversible expansion of an ideal gas[AMU 2002]

Thermodynamics and Thermochemistry (a) W  nRT ln

V2 V1

(b) W  n e ln



(c) W  PV

19.

T2 T1

A cylinder of gas supplied by Bharat Petroleum is

14 kg assumed to contain of butane. It a normal 20 ,000 kJ family requires of energy per day for cooking, butane gas in the cylinder last for ….

2

(d) W   PdV 1

14.

Days

If an endothermic reaction is non-spontaneous at freezing point of water and becomes feasible at [AIEEE 2002]

(a) H is ve , S is +ve 20.

(c) H and S both are –ve

JK 1 mol 1

What is the entropy change (in

) when

o one mole of ice is converted into water at 0 C (The enthalpy change for the conversion of ice to

16.

at 0 C )[CBSE PMT 2003]

(a) 21.98

(b) 20.13

(c) 2.013

(d) 2.198

(b) 30.5 K

(c) 28.8 K

(d) 28800 K

N 2 H 4 (g)  2 N(g)  4 H(g) bond energy of 391 KJ mol

bond is

N H

(H )

in

(b)  43 .8 kJ mol 1

(c) 68 .0 kJ mol 1

(d) 43 . 8 kJ mol 1

Equilibrium constant of a reaction is related to

30 .5 kJ

28 . 8 JK 1

(b) Free energy change G .

(c) Temperature T

for

(d) None The standard Gibbs free energy change G o is related to equilibrium constant K p as [MP PET/PMT 1998]

22. the

1724 KJ mol

process

1

(a) K p  RT ln G

. If the

bond in ammonia is

1

G o (c) K p   RT

. What is the bond energy of N  N N2H4 [MP PMT 2004]

18.

21.

[DPMT 2004]

(a) 1059 K

change

(a)  68 .0 kJ mol 1

(a) Standard free energy change G o

The melting point of NaCl is

enthalpy

(d) 40 days

[AIIMS 1991]

One mole of NaCl (s) on melting absorbed

The

(c) 50 days

o

of heat and its entropy is increased by

17.

(b) 20 days

The heat of neutralization of HCl by NaOH under certain condition is – 55.9 kJ and that of HCN by NaOH is –12.1 kJ. the heat of ionization of HCN is [MP PET 2001]

(d) H is +ve, S is –ve

liquid water is 6.0 kJ mol

(a) 15 days

(e) 32 days

(b) H and S both are +ve

1

(a) 160 KJ mol 1

(b) 391 KJ mol 1

(c) 1173 KJ mol 1

(d) 320 KJ mol 1

23.

 e  (b) K p     RT 

(d) K p  e



G o

G o RT

this reaction is 176 .7 J / K . The standard free energy change for this reaction at 25 o C is [DCE 2004]

[DCE 2003]

(a) High dipole moment

o

The standard enthalpy or the decomposition of N 2 O5 to NO 2 is 58.04 kJ and standard entropy of

Liquid ammonia is used in refrigeration because of its

(a) –5.38 kJ

(b) 5.38 kJ

(c) 5.38 kJ

(d) –538 kJ

For the equilibrium H 2 O(l) ⇌ H 2 O(g) at 1 atm and

24.

298 K

(b) High heat of vaporisation

[AIIMS 2004]

(c) High basicity (d) All of these

[Kerala PMT 2004]

( H c of C4 H10  2658 KJ per mole )

its boiling point, then

15.

453

(a) Standard free energy change is equal to zero (G  0) o

454 Thermodynamics and Thermochemistry (b) Free energy change is less than zero (G  0 )

S  0 .066 k JK 1 mol 1 . Temperature at which free

(c) Standard free energy change is less than zero

energy change for reaction will be zero, is [MH CET 1999]

(G  0) o

(d) Standard free energy change is greater than

(a) 373 K

(b) 413 K

(c) 463 K

(d) 493 K

zero (G  0) o

25.

For reaction Ag 2 O(s)  2 Ag (s)  (1 / 2)O2 (g) the value  H  30 . 56 kJ mol 1

of

and

(SET -10)

1.

12.

40 (d) A   B

40 A   B

(b) For spontaneous reaction G should negative G  H  T S  (ve )  T (ve ) If TS  H then G will be negative reaction will be spontaneous.

H  40  40  0 .

be and

2.

(b) H  E  nRT .

13.

(b) W  PV .

3.

(c) n  1  0  1

14.

(b) H and S both are +ve than reaction is spontaneous.

15.

(a) S 

16.

(a) NaCl (s) ⇌ NaCl (l)

E  H  nRT E  176  1 

4.

5.

8 .314  1240  165 . 6 kJ . 1000

(d) A spontaneous process is accompanied by decrease in enthalpy and increase in entropy means H is negative and S is positive.

Given that : H  30 .5 KJ mol 1

 H  (b) C P    , At equilibrium T is constant i.e.  T  P

S  28 .8 JK 1  28 .8  10 3 KJ K 1

 T  0, thus C P   . 6.

By using S 

(d) E  Eele.  Enucl.  Echemical  Epotential



 Ekinetic (Et  Ev  Er ) .

7.

(c) An ideal gas under going expansion in vacuum shows, E  0, W  0 and q  0 .

8.

(b) H  q p .

9.

(c) E may be greater or lesser or equal to H .

 H  E  PV  E  nRT . 10.

11.

(d) It is a modified form of Ist law of thermodynamics. It is a conservation law of mass and energy. (a) for reaction (i) n1  0.5 for reaction (ii) n 2  1.5 So, H1  H 2

q rev 6000   21 .98 JK 1 mol 1 T 273

H T

30 . 5  1059 K 28 . 8  10 3

H H |

17.

|

(a) H  N  N  H (So, 4 N  H bond present) means their energy  391  4  1564 so the bond energy of N  N in N 2 H 4  1724  1564  160 KJ / mol

18.

(b) Ammonia has high heat of vaporisation hence is used in refrigeration.

19.

(e) Calorific value of butane H c 2658    45 .8 KJ / gm mol. wt. 58 Cylinder

consist

14 Kg

of

14000 gm of butane  1gm gives

45 .8 KJ

butane

means

Thermodynamics and Thermochemistry

14000 gm gives

14000  45.8

 641200 KJ Family need 20,000 KJ / day So gas full fill the requirement for 641200  32 .06 days 20 ,000

20.

(d)

21.

(a) G o  2 .303 log k .

22.

(d) K p  e  G

23.

(d)

24.

(b) For reaction H 2 O(l) ⇌ H 2 O(g)

o

/ RT

.

n  1 means positive so when n is positive then G  0 . 25.

(c) G  H  TS

G  0 at equilibrium  H  TS or 30.56  T  0.066 T  463 K .

***

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