Chemistry: Topic-wise Test- 3 - NEET MCQ

For 0.3 g of Ca(OH)₂ dissolved in water to give 500 mL of solution:

∆H_reaction = (∆H_Product - ∆H_reactant)
= (-635.1 - 393.5)-(-1206.9) = 178.3 kJ mol^-1
So, we can say that the reaction is endothermic in nature. 
So, an increase in temperature will drive the reaction in a forward direction. (According to Le Chetelier principle-a principle stating that if a constraint (such as a change in pressure, temperature, or concentration of a reactant) is applied to a system in equilibrium, the equilibrium will shift so as to tend to counteract the effect of the constraint.)

Le Chaterlier principle is used.

According to Lewis concept, a positively charged or an electron deficient species acts as Lewis acid. BF₃ is an electron deficient compound with B having 6 electrons only.

H =U+pV. H is enthalpy of reaction.

Entropy is a state function and it is measure of randomness of a system.

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

when 1 mole of CO₂ is produced energy released is –393.5 kJ mol⁻¹ Moles of CO₂ given =35.2/44 =0.8 moles So energy released = 0.8 x393.5 KJ/mol = 315 KJ/mol

In case 1, the bond is broken in oxygen’s favor and it will attain its octet. Also, carbon becomes sp² hybridized, so there is a chance of polarity.
In case 2, if the bond is broken in favor of oxygen, then the ring will become anti-aromatic which is highly unstable and the bond won’t be broken in that way. If the bond is broken in favor of carbon in the ring, then although the ring becomes aromatic but oxygen will bear +ve charge which is very unstable. So, there is no chance to break the bond. 
In case 3, if the double bond is broken in favor of oxygen, then oxygen will acquire a negative charge and the ring will become aromatic. So, it is a highly favorable case of double bond breaking.
Therefore, the order of polarity: - III>I>II

The correct answer is Option D.
In 1,3,5-cyclohexatriene, there are three C = C having a bond length 134 pm and three C - C having a bond length 154 pm. In benzene, all the six C - C bonds have the same bond length 139 pm. 
 

The correct answer is Option C.
ΔH_hyd (cyclohexene) = - 119 kJ/mol (1C = C)
ΔH_exp (benzene) = -3 × 119 = -357 (3C = C)
ΔH_cal (benzene) = -208 KJ/mol
∴ resonance energy = ΔH_exp - ΔH_cal
                                        = -357 + 208
                                 = -149 kJ/mol
 

Here, we can see that Nitrogen gave its lone pair to make the system aromatic. The same case happens with option b and d. But with option c, Boron is not having any lone pair to donate. So option c is correct answer

In the compound I, Br will dispatch as Br⁺ so that a -ve charge appears on carbon which will give us 6π electrons. So ring will become aromatic.(4n+2 π electron is needed for aromaticity)
In compound II, Br will dispatch as Br-. So that carbon has +ve charge and all the double bond will circulate in the ring. This will maintain 4n+2 π electron and the molecule will remain as aromatic.

The correct answer is Option D.

1, 3, 5, 7-cyclooctatetraene is a system with 8 electrons but it is a nonaromatic compound as it adopts a tub like shape to escape anti-aromaticity. Hence, d option is wrong.

• Chain isomerism occurs due to the possibility of branching in carbon chains.
• Geometrical isomerism or configurational isomerism or cis-trans isomerism arises when the functional group are present on same side of carbon or are on opposite side of the carbon chain.
• Metamerism arises when organic compounds have the same molecular formula but different alkyl groups on either side of the functional group.
• In C₂H₅OC₂H₅ and CH₃OCH₂CH₂CH₃  , we can see that in diethyl ether we have 2 carbon atoms on the left side of oxygen but in methyl propyl ether we have one carbon atom on the left of oxygen. On the right hand side of oxygen, we have 2 carbon atoms but in methyl propyl ether, we have 3 carbon atoms.

So, we can say that above molecules are metamers. Therefore, option C is correct.

For positional isomerism in alkene 4C-atom required →

For geometrical isomerism in alkene also 4c–atom required →

There are 3 different positions of hydrogen. Hence, 3 structural isomers are possible.

Cis-trans Isomers:- It is under the class of geometric isomer,

• It exists in alkenes (organic molecules which have double bonds). 
• When two similar or higher priority groups are attached to the carbon on the same side, it is termed as cis isomer and when it is attached to the opposite side it is called a trans isomer.

Alkenes like 1-hexene when flipped from top to bottom they have identical structures and also they have C=CH₂ unit which does not exist as cis-trans isomers.

Answer: (b), The IUPAC name of aforementioned compound is 1,1 –dimethyl -3-cyclohexanol.

∆S_X→Z = ∆S_X→Y + ∆S_Y→Z(Entropy is a state function, so it is additive)
W_X→Y→Z = WX→Y (work done in _y→z is zero as the process is isochoric)

Volume in (I) = nRT/P₁ = 1× 0.0821× 298/4 = 6.11 L
Volume in (II) = nRT/P₂ = 1× 0.0821× 298/2 = 12.23 L
Total volume = 18.34 L
Applying PV = nRT at final condition, 
P = 2× 0.0821× 298/18.34 = 2.66

∆S_X→Y = ∆S_X→Z + ∆S_Z→Y(Entropy is a state function, so it is additive)
However, ∆S_X→Z is zero. As for adiabatic process. There is no change in entropy. 
∆S_X→Y =  ∆S_Z→Y = 2.303 5 8.314 log(10/1) = 95.7 JK^-1