Q. Fo an ideal gas, consider only P-V work in going from initial state X to the final state Z. The final state Z can be reached by either of the two paths shown in the figure.

[Take

△

S as change in entropy and W as work done].
Which of the following choice(s) is (are) correct?
(2012)

$△ S_{X \to Z} = △ S_{X \to Y} + △ S_{Y \to Z}$
$W_{X \to Z} = W_{X \to Y} + W_{Y \to Z}$
$W_{X \to Z △ Z} = W_{X \to Y}$
$△ S_{X \to Y \to Z} = △ S_{X \to Y}$

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Q. 1 mole of an ideal gas at

25^{\circ} C

is subjected to expand reversibly and adiabatically to ten times of its initial volume. Calculate the change in entropy during expansion.

19.15 $J K^{- 1} m o l^{- 1}$
-29.15 $J K^{- 1} m o l^{- 1}$
4.7 $J K^{- 1} m o l^{- 1}$
Zero

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Q. Calculate the enthalpy of vaporisation (in

k J / m o l

) for ethanol. Given, entropy change for the process is

109 J K^{- 1} m o l^{- 1}

and boiling point of ethanol is

78.5^{o} C .

$50.29 k J m o l^{- 1}$
$12.58 k J m o l^{- 1}$
$63.52 k J m o l^{- 1}$
$38.31 k J m o l^{- 1}$

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Entropy is a state function.

True
False

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Q. The entropy change can be calculated by using the expression,

△ S = \frac{Q_{r e v}}{T} .

When water freezes in a glass beaker, choose the correct statement amongst the following:

$△ S_{s y s t e m}$ decreases but $△ S_{s u r r o u n d i n g s}$ remains the same.
$△ S_{s y s t e m}$ increases but $△ S_{s u r r o u n d i n g s}$ decreases.
$△ S_{s y s t e m}$ decreases but $△ S_{s u r r o u n d i n g s}$ increases.
$△ S_{s y s t e m}$ decreases and $△ S_{s u r r o u n d i n g s}$ also decreases.

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Q. Consider the following statements about entropy.

It is an extensive property.
It is a path function.
All natural processes are sponteneous.
Entropy is the measurement of the randomness of the system.

The number of the statements which are true out of the above statements is/are:

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Q. Generally alkali metals form their oxides by an average increase of

6 k J m o l^{- 1} K^{- 1}

in their entropies.If at

25^{o} C, △ G_{f}^{o} o f A l_{2} O_{3} (s) = - 1582 k J m o l^{- 1}; △ H_{f}^{o} o f L i_{2} O (s) = 1244 k J / m o l a n d △ H_{f}^{o}

N a_{2} O (s) = 1411 k J / m o l .

The aluminium oxide can be reduced to Al metal by which metal.

$N a$
$L i$
both
none

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Q. Calculate the change of entropy

Δ_{r} S_{m}^{\circ}

at 298 K for the reaction in which urea is formed from

N H_{3}

and

C O_{2}

. The standard entropy of

N H_{2} C O N H_{2}

is 174.0

J K^{- 1} m o l^{- 1}

. For

N H_{3}

C O_{2}

and

H_{2} O

it is 192.3, 213 and 69.9

J K^{- 1}

$- 354.4 J K^{- 1}$
$354.4 J K^{- 1}$
$- 453.4 J K^{- 1}$
$453.4 J K^{- 1}$

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Q. Two blocks of the same metal having same mass and at temperature

T_{1}

and

T_{2}

respectively, are brought in contact with each other and allowed to attain thermal equilibrium at constant pressure. The change in entropy,

△ S

for this process is

$2 C_{p} l n [\frac{T_{1} + T_{2}}{2 T_{1} T_{2}}]$
$C_{p} l n [\frac{(T_{1} + T_{2})^{2}}{4 T_{1} T_{2}}]$
$2 C_{p} l n [\frac{(T_{1} + T_{2})^{2}}{4 T_{1} T_{2}}]$
$2 C_{p} l n ⎡ ⎢ ⎢ ⎢ ⎢ ⎣ \frac{(T_{1} + T_{2})^{\frac{1}{2}}}{4 T_{1} T_{2}} ⎤ ⎥ ⎥ ⎥ ⎥ ⎦$