Thermodynamics Online Objective Test | Thermodynamics Online Objective Test

# Thermodynamics # CBSE 11TH CHEMISTRY Prepare / Learn

Q1. A reaction, A + B → C + D + q is found to have a positive entropy change. The reaction will be

A. spontaneous only at low temperature.

B. nonspontaneous at all temperature.

C. spontaneous at all temperature.

D. spontaneous only at high temperature.

Answer : Option C
Explaination / Solution:

ΔG = ΔH -T ΔS ΔS is positive and ΔH is negative as heat is liberated in the reaction. so ΔG is negative hence reaction will be spontaneous at all temperature.

# Thermodynamics # CBSE 11TH CHEMISTRY Prepare / Learn

Q2. In a process, 701 J of heat is absorbed by a system and 394 J of work is done by the system. What is the change in internal energy for the process?

A. ΔU = 367 J

B. ΔU = 347 J

C. ΔU = 307 J

D. ΔU = 327 J

Answer : Option C
Explaination / Solution:

ΔU = q + w (1st law of thermodynamics) q = +701J (heat is absorbed by system) w = -394 J (work is done by system) ΔU = 701- 394 = 307J

# Thermodynamics # CBSE 11TH CHEMISTRY Prepare / Learn

Q3. The reaction of cyanamide, N

H_{2}

CN (s), with dioxygen was carried out in a bomb calorimeter, and

Δ U

was found to be 742.7 kJ

mo l^{_1}

at 298 K. Calculate enthalpy change for the reaction at 298 K. N

H_{2}

CN(g) +

\frac{3}{2}

O_{2} (g) \to N_{2} (g) + C O_{2} (g) + H_{2} O (l)

A. -767.8 kJ

B. -741.5 kJ

C. -702.2 kJ

D. 741.5 kJ

Answer : Option B
Explaination / Solution:

Δ H^{0} = Δ U^{0} + Δ n_{g}

RT where Δng = 2-((3/2)+1)

# Thermodynamics # Prepare / Learn

Q4. Calculate the number of kJ of heat necessary to raise the temperature of 60.0 g of aluminium from 35

^{\circ} C

to 55

^{\circ} C

. Molar heat capacity of Al is 24 J

mo l^{- 1} K^{- 1}

A. 1.34 kJ.

B. 1.52 kJ.

C. 1.78 kJ.

D. 1.09 kJ.

Answer : Option D
Explaination / Solution:

q=nC ΔT where n= 60.0/27 mole and ΔT = 20 K and C = 24J/mol K

# Thermodynamics # CBSE 11TH CHEMISTRY Prepare / Learn

Q5. Calculate the enthalpy change on freezing of 1.0 mol of water at 10.0

^{\circ} C

to ice at -10.0

^{\circ} C

Δ_{fus}

H = 6.03 kJ

mo l^{- 1}

at 0

^{\circ} C

C_{p} [H2O (l)] = 75 . 3 J mo l^{- 1} K^{- 1}

C_{p} [H2O (s)] = 36 . 8 J mo l^{- 1} K^{- 1}

A. ΔH = −5.231 kJ mol−1

B. ΔH = −7.415 kJ mol−1

C. ΔH = −6.415 kJ mol−1

D. ΔH = −6.114 kJ mol−1

Answer : Option C
Explaination / Solution:

Δ H = Δ H_{1} + Δ H_{2} + Δ H_{3}

# Thermodynamics # CBSE 11TH CHEMISTRY Prepare / Learn

Q6.

Enthalpy of combustion of carbon to

C O_{2}

is –393.5 kJ

mol -^{1}

. Calculate the heat released upon formation of 35.2 g of

C O_{2}

from carbon and dioxygen gas.

A. -315 kJ

B. -398 kJ

C. -375 kJ

D. -275 kJ

Answer : Option A
Explaination / Solution:

when 1 mole of

C O_{2}

is produced energy released is –393.5 kJ

m o l^{- 1}

Moles of

C O_{2}

given =35.2/44 =0.8 moles So energy released = 0.8 x393.5 KJ/mol = 315 KJ/mol

# Thermodynamics # CBSE 11TH CHEMISTRY Prepare / Learn

Q7. Enthalpies of formation of CO(g),

C O_{2} (g)

N_{2} O (g)

and

N_{2} O_{4} (g)

are -110, –-393, 81 and 9.7 kJ

mo l^{- 1}

respectively. Find the value of

Δ_{r} H

for the reaction:

N_{2} O_{4} (g) + 3CO (g) \to N_{2} O (g) + 3C O_{2} (g)

A. 36.2 kJ

mo l^{- 1}

B. -56.2 kJ

mo l^{- 1}

C. -46.2 kJ

mo l^{- 1}

D. -40.2 kJ

mo l^{- 1}

Answer : Option C
Explaination / Solution:

# Thermodynamics # CBSE 11TH CHEMISTRY Prepare / Learn

Q8. Given

N_{2} (g) + 3 H_{2} (g) \to 2N H_{3} (g); Δ_{r} H^{0}

= –-92.4 kJ

mol -^{1}

What is the standard enthalpy of formation of

N H_{3}

gas?

A. -56.5 kJ

mo l^{- 1}

B. -46.2 kJ

mo l^{- 1}

C. -41.3 kJ

mo l^{- 1}

D. -36.9 kJ

mo l^{- 1}

Answer : Option B
Explaination / Solution:

Standard Enthalpy of formation of NH3 is the energy change that take place when 1 mole of NH3 is formed from elements in standard state. For 2 moles of ammonia formation energy= –-92.4 kJ

m o l^{- 1}

. For 1 mole energy =0.5 x–-92.4 kJ

m o l^{- 1}

= -46.2 kJ

m o l^{- 1}

# Thermodynamics # CBSE 11TH CHEMISTRY Prepare / Learn

Q9. For an isolated system, ΔU = 0, what will be ΔS?

A. ΔS = 0

B. ΔS < 0

C. ΔS will increase for some time and then reduce

D. ΔS > 0

Answer : Option A
Explaination / Solution:

for isolated system ΔS = 0.

# Thermodynamics # CBSE 11TH CHEMISTRY Prepare / Learn

Q10. for the reaction at 298 K,

2A + B \to C

= 400 kJ

mo l^{- 1}

and

Δ S

= 0.2 kJ

K^{- 1} mo l^{- 1}

At what temperature will the reaction become spontaneous considering

Δ H

and

Δ S

to be constant over the temperature range.

A. 3500 K

B. 2000 K

C. 1500 K

D. 2500 K

Answer : Option B
Explaination / Solution:

ΔG= ΔH-TΔS At equilibrium ΔG=0 then T= ΔH/ΔS =2000K

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