﻿ Medical Entrance Exam Question and Answers | Thermodynamics - Zigya

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# Thermodynamics

#### Multiple Choice Questions

11.

Assertion : BaCO3 is more soluble in HNO3 than in plain water.

Reason : Carbonate is a weak base and reacts with the H+ from the strong acid, causing the barium salt to dissociate.

• If both assertion and reason are true and the reason is the correct explanation of the assertion.

• If both assertion and reason are true and the reason is not the correct explanation of the assertion.

• If assertion is true but reason is false.

• If both assertion and reason are false.

A.

If both assertion and reason are true and the reason is the correct explanation of the assertion.

BaCO3 is more soluble in HNO3 than in plain water as Carbonate is a weak base and reacts with the H+ from the strong acid, causing the barium salt to dissociate.

BaCO3 + 2HNO3 → Ba(NO3)2 + H2O + CO2

12.

Which one of the following has $∆$S° greater than zero?

• CaO(s) + CO2(g) $⇌$ CaCO3(s)

• NaCl(aq) $⇌$NaCl(s)

• NaNO3(s) $⇌$ Na+(aq) + NO3-(aq)

• N2(g) + 3H2(g) $⇌$ 2NH3(g)

C.

NaNO3(s) $⇌$ Na+(aq) + NO3-(aq)

Among the following options, option c is correct. It is because the number of product species is greater than the number of reactant species. So it leads to positive value of entropy.

13.

Energy is being emitted from the surface of a black body at 127°C the rate of 1.0 x 106 J/sm2. The temperature of the black body at which the rate of energy emission is 16.0 x 10° J/sm2 will be

• 7540C

• 5270C

• 2540C

• 5080C

B.

5270C

14.

One gram sample of NH4NO3 is decomposed in a bomb calorimeter. The temperature of the calorimeter increases by 6.12 K. The heat capacity of the system is 1.23 kJ/g/deg. What is the molar heat of decomposition for NH4NO3 ?

• -7.53 kJ/mol

• -398.1 kJ/mol

• -16.1 kJ/mol

• -602 kJ/mol

D.

-602 kJ/mol

Heat of decomposition, $∆$E = ms$∆$T = 1 × 1.23 × 6.12 = 7.5276 kJ

Molar heat of decompsoition for NH4NO3 = 7.5276 × 80 = 602.2 kJ/mol

15.

Assertion : $∆$H and $∆$E are almost the same for the reaction, N2(g) + O2(g) → 2NO(g)

Reason : All reactants and products are gases.

• If both assertion and reason are true and the reason is the correct explanation of the assertion.

• If both assertion and reason are true and the reason is not the correct explanation of the assertion.

• If assertion is true but reason is false.

• If both assertion and reason are false.

B.

If both assertion and reason are true and the reason is not the correct explanation of the assertion.

$∆$n = chnage in number of mole of products and reactant species.

N2(g) + O2(g) $⇌$ 2NO(g)

$∆$n = 2 - 2 = 0

16.

Assertion : The increase in internal energy ($∆$E) for the vapourization of one mole of water at 1 atm and 373 K is zero.

Reason : For all isothermal processes, $∆$E = 0.

• If both assertion and reason are true and the reason is the correct explanation of the assertion.

• If both assertion and reason are true and the reason is not the correct explanation of the assertion.

• If assertion is true but reason is false.

• If both assertion and reason are false.

A.

If both assertion and reason are true and the reason is the correct explanation of the assertion.

At 373 Kor 100°C, the water starts boiling and at this temperature the vaporization of water is an isothermal process.

The internal energy change ($∆$E), depend only on temperature, it follows that at constant temperature, the internal energy ofthe gas remains constant, i.e. $∆$E is zero.

17.

The potential energy diagram for a reaction R → P is given in the figure. $∆$H ° of the reaction corresponds to the energy

• a

• b

• c

• a + b

C.

c

In the above diagram, $∆$H° of the reaction corresponds to energy c.

$∆\mathrm{H}$ = activation energy of forward reaction - activation energy of backward reaction

= b - a = c

18.

In an isochoric process, the increase in internal energy is equal to:

• the sum of heat absorbed and work done

• the work done

• heat absorbed

• heat evolved

C.

heat absorbed

In an isochoric process, $∆$V = 0, hence, work done P$∆$V = W = 0. So, $∆$E = q + 0. Hence, the increase in internal energy will be equal to heat absorbed by the system.

19.

Assertion: When a bottle of cold carbonated drink is opened, a slight fog forms around the opening.

Reason:  Adiabatic expansion of the gas causes lowering of temperature and condensation of water vapours.

• if both assertion and reason are true and the reason is the correct explanation of the assertion.

• if both assertion and reason are true and the reason is not  the correct explanation  of the assertion.

• if assertion is true but reason is false

• if both assertion and reason are false statements

A.

if both assertion and reason are true and the reason is the correct explanation of the assertion.

Cold drinks are produced by injecting carbon dioxide into the drink at several atmospheres. Carbon dioxide dissolves readily even at normal atmospheric pressure. When the pressure is released (that is bottle is opened) carbon dioxide comes out of solution forming numerous bubbles and releasing the carbon dioxide back into the atmosphere. Also, in. "this process no heat is lost or gained, hence it is an adiabatic expansion.

20.

Heat of a reaction at constant pressure is equal to:

• HP - HR

• HP + HR

• HP $×$ HR

• $\frac{{\mathrm{H}}_{\mathrm{P}}}{{\mathrm{H}}_{\mathrm{R}}}$

A.

HP - HR

Heat of a reaction at constant pressure is equal to HP - HR.