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Resonance energy of benzene is – 142 kJ/mol. Given: Heat of atomization of graphite = 716 kJ/mol. Bond energies of C–H, C–C, C=C and H–H bonds are 490, 340, 620, 436 kJ/mol respectively. Then, $Δ H_{f}^{o}$ of C₆H₆is -

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Important Questions on Thermodynamics

EASY

Chemistry>Physical Chemistry>Thermodynamics>Enthalpy Change of a Reaction- Reaction Enthalpy

The enthalpy change on freezing of

1 mol

of water at

5 ° C

to ice at

- 5 ° C

is:

(Given

Δ_{fus} H = 6 kJ {mol}^{- 1}

0 ° C,

C_{p} (H_{2} O, l) = 75 .3 J {mol}^{- 1} K^{- 1}

C_{p} (H_{2} O, s) = 36 .8 J {mol}^{- 1} K^{- 1}

)

EASY

Chemistry>Physical Chemistry>Thermodynamics>Enthalpy Change of a Reaction- Reaction Enthalpy

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>Thermodynamics>Enthalpy Change of a Reaction- Reaction Enthalpy

The standard enthalpies of formation of ${CO}_{2} (g)$ $, H_{2} O (l)$ and glucose (s) at $2 5^{o} C$ are $- 400 kJ / mol$ , $- 300 kJ / mol$ and $- 1300 kJ / mol$ , respectively. The standard enthalpy combustion per gram of glucose at $2 5^{o} C$ is

( ${ΔH}_{f}^{0} = - 1300 kJ {mol}^{- 1}$ for Glucose)

MEDIUM

Chemistry>Physical Chemistry>Thermodynamics>Enthalpy Change of a Reaction- Reaction Enthalpy

Given that the bond energies of:

N \equiv N is 946 kJ {mol}^{- 1}, H - H is 435 kJ {mol}^{- 1}, N - N is 159 kJ {mol}^{- 1},

and

N - H is 389 kJ {mol}^{- 1}

, the heat of formation of hydrazine in the gas phase in

kJ {mol}^{- 1}

is:

EASY

Chemistry>Physical Chemistry>Thermodynamics>Enthalpy Change of a Reaction- Reaction Enthalpy

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

HARD

Chemistry>Physical Chemistry>Thermodynamics>Enthalpy Change of a Reaction- Reaction Enthalpy

For the reaction

N_{2} + 3 X_{2} \to 2 {NX}_{3}

where

X = F, Cl

(the average bond energies are

F - F = 155 kJ {mol}^{- 1}, N - F = 272 kJ {mol}^{- 1}, Cl - Cl = 242 kJ {mol}^{- 1}, N - Cl = 200 kJ {mol}^{- 1}

and

N \equiv N = 941 kJ {mol}^{- 1}

), the heats of reaction of

{NF}_{3}

and

{NCl}_{3}

kJ {mol}^{- 1},

respectively, are closest to

MEDIUM

Chemistry>Physical Chemistry>Thermodynamics>Enthalpy Change of a Reaction- Reaction Enthalpy

One mole of ethanol is produced reacting graphite,

H_{2}

and

O_{2}

together. The standard enthalpy of formation is

- 277.7 k J m o l^{- 1} .

Calculate the standard enthalpy of the reaction when

4

moles of graphite is involved

MEDIUM

Chemistry>Physical Chemistry>Thermodynamics>Enthalpy Change of a Reaction- Reaction Enthalpy

The heats of combustion of carbon and carbon monoxide are

- 393.5 a n d - 283.5 k J m o l^{- 1},

respectively. The heat of formation

(in kJ)

of carbon monoxide per mole is:

HARD

Chemistry>Physical Chemistry>Thermodynamics>Enthalpy Change of a Reaction- Reaction Enthalpy

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

)

HARD

Chemistry>Physical Chemistry>Thermodynamics>Enthalpy Change of a Reaction- Reaction Enthalpy

Given:

C (graphite) + O_{2} (g) \to {CO}_{2} (g); Δ_{r} H^{o} = - 393 .5 kJ {mol}^{- 1}

H_{2} (g) + \frac{1}{2} O_{2} (g) \to H_{2} O (l); Δ_{r} H^{o} = - 285 .8 kJ {mol}^{- 1}

{CO}_{2} (g) + 2 H_{2} O (l) \to {CH}_{4} (g) + 2 O_{2} (g); Δ_{r} H^{o} = + 890 .3 kJ {mol}^{- 1}

Based on the above thermochemical equations, the value of

Δ_{r} H^{o}

298 K

for the reaction

C (graphite) + 2 H_{2} (g) \to {CH}_{4} (g)

will be:

HARD

Chemistry>Physical Chemistry>Thermodynamics>Enthalpy Change of a Reaction- Reaction Enthalpy

For complete combustion of ethanol,

C_{2} H_{5} OH (l) + 3 O_{2} (g) \to 2 {CO}_{2} (g) + 3 H_{2} O (l)

,
the amount of heat produced as measured in bomb calorimeter, is

{1364.47 kJ mol}^{-1}

25 ℃

. Assuming ideality the Enthalpy of combustion,

Δ_{c} H

, for the reaction will be:

(R = {8.314 kJ mol}^{-1})

MEDIUM

Chemistry>Physical Chemistry>Thermodynamics>Enthalpy Change of a Reaction- Reaction Enthalpy

Calculate the enthalpy change. For the change $8 S (g) \to S_{8} (g)$ , given that

$H_{2} S_{2} (g) \to 2 H (g) + 2 S (g), ΔH = 239 .0 k c a l m o l^{- 1}$

$H_{2} S (g) \to 2 H (g) + S (g), ΔH = 175 .0 k c a l m o l^{- 1}$

MEDIUM

Chemistry>Physical Chemistry>Thermodynamics>Enthalpy Change of a Reaction- Reaction Enthalpy

The standard enthalpy of formation of

{NH}_{3}

- 46.0 kJ / mol

. If bond enthalpy of

H_{2}

- 436 kJ / mol

and that of

N_{2}

- 712 kJ / mol

, the average bond enthalpy of

N - H

bond in

{NH}_{3}

is :

EASY

Chemistry>Physical Chemistry>Thermodynamics>Enthalpy Change of a Reaction- Reaction Enthalpy

For a reaction,

A (g) \to A (l); ΔH = - 3 RT .

The correct statement for the reaction is

MEDIUM

Chemistry>Physical Chemistry>Thermodynamics>Enthalpy Change of a Reaction- Reaction Enthalpy

The combustion of benzene

(l)

gives

{CO}_{2} (g)

and

H_{2} O (l) .

Given that heat of combustion of benzene at constant volume is

- 3263 .9 kJ {mol}^{- 1}

25 ° C;

the heat of combustion

(in kJ {mol}^{- 1})

of benzene at constant pressure will be

(R = 8 .314 {JK}^{- 1} {mol}^{- 1})

EASY

Chemistry>Physical Chemistry>Thermodynamics>Enthalpy Change of a Reaction- Reaction Enthalpy

The difference between

∆ H

and

∆ U

(∆ H - ∆ U)

, when the combustion of one mole of heptane

(l)

is carried out at a temperature

T

, is equal to:

MEDIUM

Chemistry>Physical Chemistry>Thermodynamics>Enthalpy Change of a Reaction- Reaction Enthalpy

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:

EASY

Chemistry>Physical Chemistry>Thermodynamics>Enthalpy Change of a Reaction- Reaction Enthalpy

Identify the INVALID equation.

HARD

Chemistry>Physical Chemistry>Thermodynamics>Enthalpy Change of a Reaction- Reaction Enthalpy

The bond dissociation energies of

X_{2} Y_{2}

and

XY

are in the ratio of

1 : 0 .5 : 1 . ΔH

for the formation of

XY

- 200 kJ {mol}^{- 1}

. What will be the bond dissociation energy of

X_{2}

EASY

Chemistry>Physical Chemistry>Thermodynamics>Enthalpy Change of a Reaction- Reaction Enthalpy

For which of the following reactions,

∆ H

is equal to

∆ U

Resonance energy of benzene is – 142 kJ/mol. Given: Heat of atomization of graphite = 716 kJ/mol. Bond energies of C–H, C–C, C=C and H–H bonds are 490, 340, 620, 436 kJ/mol respectively. Then, Δ H f o of C6H6 is -

Important Questions on Thermodynamics

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Resonance energy of benzene is – 142 kJ/mol. Given: Heat of atomization of graphite = 716 kJ/mol. Bond energies of C–H, C–C, C=C and H–H bonds are 490, 340, 620, 436 kJ/mol respectively. Then, $Δ H_{f}^{o}$ of C₆H₆is -