These are Assertion-Reason type questions.Question contains two statements:Statement-1 (Assertion) and Statement-2 (Reason). Answer these question from the following four options.

Statement 1 :Absolute value of internal energy of a substance cannot be determined.
Statement 2 :It is impossible to determine exact values of constitutent energies of the substances.

Statement-1 is True, Statement-2 is True, Statement-2 is a correct explanation for Statement-1
Statement-1 is True, Statement-2 is True Statement-2 is NOT a correct explanation for Statement-1
Statement - 1 is True, Statement-2 is False
Statement -1 is False, Statement-2 is True

Solution

It is fact that absolute values of internal energy of substances cannot be determined. It is also true that it is not possible to determine exact values of constitutent energies of a substance.

Zinc can be oxidized by carbon monoxide
Zinc oxide can be reduced by graphite
Both statements (A) and (B) are true
Both statements (A) and (B) are false

Solution

For combustion reaction, ?H is negative,
?n = (16 + 18) – (25 + 2) = +7,so ?S is + ve, reaction is spontaneous, hence ?G is –ve

Solution

For spontaneous cooling of hot metal rod in air ?S_system decreases (as metal rod cools down ) and ?S_airincreases(as surrounding air becomes hot). So, ?S_system < 0 and ?S_universe > 0

Solution

?G = ?H – T?S = 177.9 – (298 × 160.4/1000) = 177.9 – 47.79 = + 130.1 kJ

Solution

If the value of C_p for nitrogen gas is 7 JK^-1 mol^-1, then the value of ?H on heating 28 g of nitrogen gas from 0°C to 100°Cat constant pressure will be :

1200 J
1300 J
1400 J
1500 J

Solution

Highest entropy is in :

hydrogen
water
graphite
mercury

Solution

Entropy is a measure of randomness of the system which is highest in gases. So, entropy of hydrogen is highest among the given options.

For a reaction in which all reactants and products are liquids,which one of the following equations is most applicable ?

?H < ?E
?H = ?S
?H = ?E
?H = ?G

Solution

As all reactants and products are liquid ?n(g) = 0
?H = ?E - ?nRT
?H = ?E (∵ \( \Delta n = 0 \) )

A chemical reaction will be spontaneous if it is accompanied by a decrease of

entropy of the system
enthalpy of the system
internal energy of the system
free energy of the system

Solution

?G is negative for a spontaneous process.

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