For the reaction, S (rhombic) + O 2 → SO 2 ΔH = - 298 kJ mol - 1 at 25 ° C and 1 atm . Therefore, Δ E for the reaction should be

- 298 + 8 . 314 × 298 kJ mol - 1

- 298 - 8 . 314 × 298 kJ mol - 1

- 298 - 2 × 8 . 314 × 298 kJ mol - 1

The reaction in which ΔH > ΔU is

CaCO 3 ( s ) ⟶ CaO ( s ) + CO 2 ( g )

N 2 ( s ) + 3 H 2 ( g ) ⟶ 2 NH 3 ( g )

CH 4 ( g ) + 2 O 2 ( g ) ⟶ CO 2 ( g ) + 2 H 2 O ( l )

N 2 ( g ) + O 2 ( g ) ⟶ 2 NO ( g )

EASY

Earn 100

The enthalpy change at constant volume is equal to the internal energy change. Justify.

Important Questions on Energetics (Thermochemistry)

HARD

Chemistry>Physical Chemistry>Energetics (Thermochemistry)>Enthalpies for Different Types of Reactions

One mole of an ideal gas at

300 K

in thermal contact with its surroundings expands isothermally from

1.0 L

2.0 L

against a constant pressure of

3.0 atm

. In this process, the change in entropy of the surroundings

(∆ S_{s u r r})

J K^{- 1}

is:

(1 L atm = 101.3 J)

MEDIUM

Chemistry>Physical Chemistry>Energetics (Thermochemistry)>Enthalpies for Different Types of Reactions

For the reaction $H_{2} F_{2} (g) \to H_{2} (g) + F_{2} (g)$

$ΔU = - 59.6 kJ {mol}^{- 1}$ at $27 ° C$

The enthalpy change for the above reaction is $(-)$ ____ ${kJmol}^{- 1}$ (nearest integer)

(Given : $R = 8.314 {JK}^{- 1} {mol}^{- 1}$ ) .

EASY

Chemistry>Physical Chemistry>Energetics (Thermochemistry)>Enthalpies for Different Types of Reactions

Consider the reaction,

N_{2} + 3 H_{2} \to 2 {NH}_{3}

, carried out at a constant temperature and pressure. If

ΔH

and

ΔU

are the enthalpy and internal energy changes for the reaction, which of the following expressions is true?

HARD

Chemistry>Physical Chemistry>Energetics (Thermochemistry)>Enthalpies for Different Types of Reactions

The entropy change associated with the conversion of

1 k g

of ice at

273 K

to water vapours at

383 K

is:

(Specific heat of water liquid and water vapour are

4.2 k J K^{-}

and

2.0 k J K^{- 1} k g^{- 1}

; heat of liquid fusion and vaporization of water are

334 k J k g^{- 1}

and

2491 k J k g^{- 1}

, respectively). (

l o g

273 = 2.436, \log 373 = 2.572, \log 383 = 2.583

)

EASY

Chemistry>Physical Chemistry>Energetics (Thermochemistry)>Enthalpies for Different Types of Reactions

For the reaction,

S_{(rhombic)} + O_{2} \to {SO}_{2}

ΔH = - 298 kJ {mol}^{- 1}

25 ° C

and

1 atm

. Therefore,

Δ E

for the reaction should be

MEDIUM

Chemistry>Physical Chemistry>Energetics (Thermochemistry)>Enthalpies for Different Types of Reactions

A process has

Δ H = 200 J m o l^{- 1}

and

Δ S = 40 J K^{- 1} m o l^{- 1} .

Out of the values given below choose the minimum temperature above which the process will be spontaneous:

MEDIUM

Chemistry>Physical Chemistry>Energetics (Thermochemistry)>Enthalpies for Different Types of Reactions

Which one of the following is the correct relation between

C_{P}

and

C_{V}

for one mole of an ideal gas? (

R

is molar gas constant)

HARD

Chemistry>Physical Chemistry>Energetics (Thermochemistry)>Enthalpies for Different Types of Reactions

The heat of atomization of methane and ethane are

360 kJ {mol}^{- 1}

and

620 kJ {mol}^{- 1}

, respectively. The longest wavelength of light capable of breaking the

C - C

bond is (Avogadro's number

= 6.023 \times 10^{23}, h = 6.62 \times 10^{- 34} J s

)

MEDIUM

Chemistry>Physical Chemistry>Energetics (Thermochemistry)>Enthalpies for Different Types of Reactions

The reaction of cyanamide,

{NH}_{2} {CN}_{(s)}

with oxygen was run in a bomb calorimeter and

ΔU

was found to be

- 742.24 kJ {mol}^{- 1}

. The magnitude of

{ΔH}_{298}

for the reaction

{NH}_{2} {CN}_{(s)} + \frac{3}{2} O_{2 (g)} \to N_{2 (g)} + O_{2 (g)} + H_{2} O_{(l)}

kJ

. (Rounded off to the nearest integer) [Assume ideal gases and

R = 8.314 J {mol}^{- 1} K^{- 1}

]

MEDIUM

Chemistry>Physical Chemistry>Energetics (Thermochemistry)>Enthalpies for Different Types of Reactions

For water

Δ_{vap} H = 41 kJ {mol}^{- 1}

373 K

and 1 bar pressure. Assuming that water vapour is an ideal gas that occupies a much larger volume than liquid water, the internal energy change during evaporation of water is

({kJmol}^{- 1})

:
[ Use

: R = 8.3 J {mol}^{- 1} K^{- 1}]

MEDIUM

Chemistry>Physical Chemistry>Energetics (Thermochemistry)>Enthalpies for Different Types of Reactions

The process with negative entropy change is:

EASY

Chemistry>Physical Chemistry>Energetics (Thermochemistry)>Enthalpies for Different Types of Reactions

The reaction in which

ΔH > ΔU

MEDIUM

Chemistry>Physical Chemistry>Energetics (Thermochemistry)>Enthalpies for Different Types of Reactions

Given:

(i)

C (graphite) + O_{2} (g) \to {CO}_{2} (g);

{ΔrH}^{Θ} = x kJ {mol}^{- 1}

(ii)

C (graphite) + \frac{1}{2} O_{2} (g) \to CO (g);

{ΔrH}^{Θ} = y kJ {mol}^{- 1}

(iii) CO (g) + \frac{1}{2} O_{2} (g) \to {CO}_{2} (g);

{ΔrH}^{Θ} = z kJ {mol}^{- 1}

Based on the above thermochemical equations, find out which one of the following algebraic relationships is correct?

EASY

Chemistry>Physical Chemistry>Energetics (Thermochemistry)>Enthalpies for Different Types of Reactions

The correct thermodynamic conditions for the spontaneous reaction at all temperatures is:

EASY

Chemistry>Physical Chemistry>Energetics (Thermochemistry)>Enthalpies for Different Types of Reactions

The heat of combustion of carbon to

C O_{2}

- 393.5 kJ / mol

. The heat released upon the formation of

35.2 g

C O_{2}

from carbon and oxygen gas is

MEDIUM

Chemistry>Physical Chemistry>Energetics (Thermochemistry)>Enthalpies for Different Types of Reactions

For which of the following processes,

∆ S

is negative?

EASY

Chemistry>Physical Chemistry>Energetics (Thermochemistry)>Enthalpies for Different Types of Reactions

For a sample of perfect gas, when its pressure is changed isothermally from

p_{i}

p_{f}

, the entropy change is given by

HARD

Chemistry>Physical Chemistry>Energetics (Thermochemistry)>Enthalpies for Different Types of Reactions

For combustion of one mole of magnesium in an open container at

300 K

and

1

bar pressure,

Δ_{C} H^{⊖} = - 601.70 kJ {mol}^{- 1}

, the magnitude of change in internal energy for the reaction is

kJ

. (Nearest integer)
(Given :

R = 8.3 J K^{- 1} {mol}^{- 1}

)

MEDIUM

Chemistry>Physical Chemistry>Energetics (Thermochemistry)>Enthalpies for Different Types of Reactions

The internal energy change (in $J$ ) when $90 g$ of water undergoes complete evaporation at $100 ° C$ is ..............

(Given : ${ΔH}_{vap}$ for water at $373 K = 41 kJ / mol$ , $R = 8.314 {JK}^{- 1} {mol}^{- 1}$ )

MEDIUM

Chemistry>Physical Chemistry>Energetics (Thermochemistry)>Enthalpies for Different Types of Reactions

For silver,

C_{p} (J K^{- 1} m o l^{- 1}) = 23 + 0.01 T .

If the temperature

(T)

3

moles of silver is raised from

300 K t o 1000 K a t 1 a t m

pressure, the value of

Δ H

will be close to:

The enthalpy change at constant volume is equal to the internal energy change. Justify.

Important Questions on Energetics (Thermochemistry)

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