Tag: chemistry

Questions Related to chemistry

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

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

  1. the reaction is both spontaneous and at equilibrium

  2. the system is at equilibrium at standard conditions

  3. the reaction is non spontaneous at standard conditions

  4. the reaction is spontaneous at standard conditions

  5. the reaction is both non spontaneous and at equilibrium

Show answer
Correct Option: B
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.

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

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

  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. $\Delta { G }^{ o }<0,{ K } _{ eq. }<1$

Show answer
Correct Option: A
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 $A$.

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
$K _{f} \left {Au(CN) _{2}^{-}\right ) = X$
$O _{2} + 2H _{2}O + 4e^{-}\rightarrow 4OH^{-}; E^{\circ} = +0.41\ volt$
$Au^{3+} + 3e^{-}\rightarrow Au; E^{\circ} = + 1.5\ volt$
$Au^{3+} + 2e^{-} \rightarrow Au^{+}; E^{\circ} = + 1.4\ volt$.

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

  1. $-RT\ ln\ X + 1.29\ F$

  2. $-RT\ ln\ X - 2.11\ F$

  3. $-RT\ ln \dfrac {1}{X} + 2.11\ f$

  4. $-RT\ ln\ X - 1.29\ F$

Show answer
Correct Option: A

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

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

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

  1. 5

  2. 10

  3. 95

  4. 100

Show answer
Correct Option: B
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$

The commercial name of polyacrylonitrile is:

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

  1. dacron

  2. orlon (acrilan)

  3. PVC

  4. bakelite

Show answer
Correct Option: B
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.

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

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

  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

Show answer
Correct Option: C
Explanation:

Uses of bakelite:

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

So the incorrect option is [C}.

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

  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)

Show answer
Correct Option: C
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}.

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

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

  1. polymerization, melamine

  2. vulcanization, resin

  3. cross-liking, bakelite

  4. condensation, polystyrene

Show answer
Correct Option: C
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].

What are blended fibres?

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

  1. Mixture of two natural fibres

  2. Mixture of two synthetic fibre

  3. Mixture of natural and synthetic fibres

  4. All of above

Show answer
Correct Option: D
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.

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

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

  1. Teflon

  2. Orlon

  3. Polythene

  4. Nylon-6

Show answer
Correct Option: A
Explanation:

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


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