# Topic: Thermodynamics (Test 1)

Topic: Thermodynamics
Q.1
Thermodynamics is the branch of physical science concerned with
A. heat and its transformations to and from other forms of energy
B. mass and its transformations to and from other forms of energy
C. kinetic energy and its transformations to and from other forms of energy
D. Potential and its transformations to and from other forms of energy
Explaination / Solution:

Thermodynamics deals with heat and its transformation from one form to another. The branch of physical science that deals with the relations between heat and other forms of energy (such as mechanical, electrical, or chemical energy), and, by extension, of the relationships between all forms of energy.

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Q.2
If  is the final volume and  is the initial volume and  the external pressure the work done can be calculated by
A. Vi0pexdV
B.
0VfpexdV
C.
D.
ViVfpexdV
Explaination / Solution:

ViVfpexdV
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Q.3
Calorimetry is a branch of science dealing with
A. measuring the maximum pressure developed in a reaction
B. measuring the amount of energy transferred as heat
C. measuring the amount of work done in a reaction
D. measuring the amount of chemicals consumed
Explaination / Solution:

Calorimetry is a branch of science dealing with measuring the amount of energy transferred as heat

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Q.4
According to Hess’s Law if a reaction takes place in several steps then its standard reaction enthalpy is
A. the difference of the standard enthalpies of the intermediate reactions into which the overall reaction may be divided at the same temperature
B. the sum of the standard enthalpies of the intermediate reactions into which the overall reaction may be divided at 35
C. the sum of the standard enthalpies of the intermediate reactions into which the overall reaction may be divided at the same temperature
D. the sum of the standard enthalpies of the intermediate reactions into which the overall reaction may be divided at 2 bar
Explaination / Solution:

Hess’s Law states that the sum of the standard enthalpies of the intermediate reactions into which the overall reaction may be divided at the same temperature.

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Q.5
Spontaneity in the context of chemical thermodynamics means
A. having the potential to proceed instantaneously
B. having the potential to proceed fast
C. having the potential to proceed without the assistance of external agency
D. having the potential to proceed with the assistance of external agency
Explaination / Solution:

spontaneity means a reaction occurring on its own without any help of external agency.

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Q.6
A thermodynamic state function is a physical quantity
A. used to determine heat changes
B. whose value is independent of path
C. used to determine pressure volume work
D. whose value depends on temperature only
Explaination / Solution:

State function is one which is only dependent on initial and final state of the system and is independent of the path by which that change has occurred.

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Q.7
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.
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.

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Q.8
Enthalpy of combustion of carbon to is –393.5 kJ . Calculate the heat released upon formation of 35.2 g of from carbon and dioxygen gas.

A. -315 kJ
B. -398 kJ
C. -375 kJ
D. -275 kJ
Explaination / Solution:

when 1 mole of  is produced energy released is –393.5 kJ Moles of given =35.2/44 =0.8 moles So energy released = 0.8 x393.5 KJ/mol = 315 KJ/mol

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Q.9
for the reaction at 298 K,    = 400 kJ and  = 0.2 kJ  At what temperature will the reaction become spontaneous considering  and  to be constant over the temperature range.
A. 3500 K
B. 2000 K
C. 1500 K
D. 2500 K
Explaination / Solution:

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

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Q.10