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Multiple choice chemistry energetics and thermochemistry gibbs energy change and equilibrium gibbs free energy entropy and spontaneity

If $\Delta G$ standard is zero, this means :

  1. <font><font class="">the reaction is both spontaneous and at equilibrium</font></font>

  2. <font><font>the system is at equilibrium at standard conditions</font></font>

  3. <font><font class="">the reaction is non spontaneous at standard conditions</font></font>

  4. <font><font>the reaction is spontaneous at standard conditions</font></font>

  5. <font><font>the reaction is both non spontaneous and at equilibrium</font></font>
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

If $\Delta G = 0$ this means, the system is at equilibrium at standard conditions.
$\Delta G = 0$, it means the reaction is equilibrium at standard conditions.
A negative value of $\Delta G  $, means spontaneous.
A positive value of $\Delta G $, means non-spontaneous.

Multiple choice chemistry energetics and thermochemistry gibbs energy change and equilibrium gibbs free energy entropy and spontaneity

If ${E} _{cell}^{o}$ for a given reaction is negative, which gives the correct relationships for the values of $\Delta { G }^{ o }$ and ${K} _{eq.}$?

  1. $\Delta { G }^{ o }>0,{ K } _{ eq. }<1$
  2. $\Delta { G }^{ o }>0,{ K } _{ eq. }>1$
  3. $\Delta { G }^{ o }<0,{ K } _{ eq. }>1$
  4. $\Delta { G }^{ o }<0,{ K } _{ eq. }<1$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
$\mathbf{Explanation:}$

From the relation between change in free energy$(\Delta G)$ and equilibrium constant $(K _{eq})$ we have :

$\mathbf{\Delta G=-RTlnK _{eq}}$      $\mathbf{\rightarrow (1)}$

where:
$\Delta G=$ The change in free energy
$R=$ Gas constant
$T=$ The absolute temperature
$K _{eq}=$ Equilibrium constant
 
From the relation between change in energy $\Delta G$ and $E _{cell}(E^{o})$ we have :

$\mathbf{\Delta G=-nFE^{o}}$ $\mathbf{\rightarrow (2)}$

$\Delta G=$ The change in free energy
$E^{o}=E _{cell}$
$n =$ moles of e- from balanced redox reaction
$F =$ Faraday's constant 

From equation  $(2) $ if $E^{o}< 0$ then $\Delta G>0$$\mathbf{\rightarrow (3)}$

If then $lnK<1$ and then $K _{eq}<1$ that is positive $\mathbf{\rightarrow (4)}$ 

From $(3)$ and $(4)$ we get that

$\mathbf{\Delta G>0}$ and $\mathbf{K _{eq}}<1$

Hence the correct answer is option $A$.
Multiple choice chemistry energetics and thermochemistry gibbs energy change and equilibrium gibbs free energy entropy and spontaneity

Consider the reaction of extraction of gold from its ore
$Au + 2CN^{-} (aq.) + \dfrac {1}{4}O _{2}(g) + \dfrac {1}{2}H _{2}O\rightarrow Au(CN) _{2}^{-} + OH^{-}$
Use the following data to calculate $\triangle G^{\circ}$ for the reaction
$K _{f} \left {Au(CN) _{2}^{-}\right ) = X$
$O _{2} + 2H _{2}O + 4e^{-}\rightarrow 4OH^{-}; E^{\circ} = +0.41\ volt$
$Au^{3+} + 3e^{-}\rightarrow Au; E^{\circ} = + 1.5\ volt$
$Au^{3+} + 2e^{-} \rightarrow Au^{+}; E^{\circ} = + 1.4\ volt$.

  1. $-RT\ ln\ X + 1.29\ F$
  2. $-RT\ ln\ X - 2.11\ F$
  3. $-RT\ ln \dfrac {1}{X} + 2.11\ f$
  4. $-RT\ ln\ X - 1.29\ F$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The standard Gibbs free energy change for the reaction is calculated using the standard cell potential. The reaction involves oxidation of Au and reduction of O2. The expression involves the formation constant X and the standard potentials provided.

Multiple choice chemistry energetics and thermochemistry gibbs energy change and equilibrium gibbs free energy entropy and spontaneity

The value of $log _{10}$ K for a reaction $A\rightleftharpoons B$ is:

$( Given : \Delta _{r}H^{0} _{298k}=-54.07 kJ mol^{-1},$ $\Delta _{r}S^{0} _{298k}=10JK^{-1}mol^{-1}$ $and\ R=8.314 JK^{-1}mol^{-1};$ 
$2.303\times 8.314\times 298=5705 )$

  1. 5

  2. 10

  3. 95

  4. 100
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$\Delta G^{0}=\Delta H^{0}-T\Delta S^{0}=-54.07 \times 1000 - 298 \times 10$

$=-54070-2980=-57050$

$\Delta G^{0}=-2.303 RT log _{10}K$

$-57050=-2.303\times 298\times 8.314 log _{10}K=-5705 log _{10}K$


$ log _{10}K=10$

Multiple choice chemistry polymer polymers of commercial importance some commercially important polymers condensation polymers

The commercial name of polyacrylonitrile is:

  1. dacron

  2. orlon (acrilan)

  3. PVC

  4. bakelite
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The commercial name of polyacrylonitrile is orlon or acrilan,

The addition polymerisation of acrylonitrile in presence of a peroxide catalyst leads to the formation of polyacrylonitrile. Polyacrylonitrile is used as a substitute for wool in making commercial fibers.

Multiple choice chemistry polymer polymers of commercial importance some commercially important polymers condensation polymers

Few polymers are matched with their uses. Point out the wrong match.

  1. Polyester - Fabric, tyre cords, safety belts

  2. Nylon 6 - Ropes, tyre cords, fabrics

  3. Bakelite - Packaging industry, lubricant

  4. Teflon - Oil seals, gaskets, non-stick utensils
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Uses of bakelite:

  • For making combs, phonograph records, electrical switches,
  • For making handles of various utensils,
  • Paints

So the incorrect option is [C}.

Multiple choice chemistry polymer polymers of commercial importance some commercially important polymers condensation polymers

Match the column I with column II and mark the appropriate choice.

Column I Column II
(A) Raincoats, hand bags (i) PHBV
(B) Laminated sheets (ii) PVC
(C) Television cabinets (iii) Urea-formaldehyde resin
(D) Orthopaedic devices (iv) Polystyrene
  1. (A) $\rightarrow$ (i), (B) $\rightarrow$ (ii), (C) $\rightarrow$ (iii), (D) $\rightarrow$ (iv)
  2. (A) $\rightarrow$ (iv), (B) $\rightarrow$ (i), (C) $\rightarrow$ (ii), (D) $\rightarrow$ (iii)
  3. (A) $\rightarrow$ (ii), (B) $\rightarrow$ (iii), (C) $\rightarrow$ (iv), (D) $\rightarrow$ (i)
  4. (A) $\rightarrow$ (iii), (B) $\rightarrow$ (iv), (C) $\rightarrow$ (i), (D) $\rightarrow$ (ii)
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
 Raincoats, handbags  (ii) PVC
 Laminated sheets  (iii) Urea-formaldehyde resin
 Television cabinets  (iv) Polystyrene
 Orthopedic devices  (i) PHBV

Uses of polyesters- it is crease resistant and is used in blending with cotton and wool fibers and also as glass reinforcing materials in safety helmets, etc.

So the correct option is [C}.

Multiple choice chemistry polymer polymers of commercial importance some commercially important polymers condensation polymers

Novolac on heating with formaldehyde undergoes _______ to form an infusible solid mass called _______.

  1. polymerization, melamine

  2. vulcanization, resin

  3. cross-liking, bakelite

  4. condensation, polystyrene
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

On heating with formaldehyde undergoes crosslinking and form a thermosetting polymer named as$bakalite$.

These are obtained by the condensation reaction of phenol with formaldehyde in the presence of either an acid or a base catalyst. The reaction starts with the initial formation of $o-and/or p-hydroxymethylphenol$ derivatives, which further react with phenol to form compounds having rings joined to each other through –CH2 groups. The initial product could be a linear product – Novolac used in paints.
The correct option is [C].

Multiple choice chemistry polymer polymers of commercial importance some commercially important polymers condensation polymers

What are blended fibres?

  1. Mixture of two natural fibres

  2. Mixture of two synthetic fibre

  3. Mixture of natural and synthetic fibres

  4. All of above
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Blended fibres are made by combining various fibres to enhance the property of the product. For eg: spandex and cotton is a natural mix for sports clothing and undergarments to improve stretching properties and prevent odour. A blended fabric helps overcome the disadvantages of natural and synthetic fibre.

Multiple choice chemistry polymer polymers of commercial importance some commercially important polymers condensation polymers

$C{F} _{2} = C{F} _{2}$ is a monomer of:

  1. Teflon

  2. Orlon

  3. Polythene

  4. Nylon-6
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Tetrafluorothylene $C{F} _{2} = C{F} _{2}$ is a monomer of Teflon $ { \left( -C{ F } _{ 2 }-C{ F } _{ 2 }- \right)  } _{ n }$.


             $n  C{ F } _{ 2 } = C{ F } _{ 2 }   \rightarrow   { \left( -C{ F } _{ 2 }-C{ F } _{ 2 }- \right)  } _{ n }$