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 )

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Which of the following statements is correct about the heat of combustion?

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Important Questions on Chemical Thermodynamics

EASY

Chemistry>Physical Chemistry>Chemical Thermodynamics>Thermochemistry

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>Chemical Thermodynamics>Thermochemistry

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

HARD

Chemistry>Physical Chemistry>Chemical Thermodynamics>Thermochemistry

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>Chemical Thermodynamics>Thermochemistry

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:

MEDIUM

Chemistry>Physical Chemistry>Chemical Thermodynamics>Thermochemistry

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

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Chemistry>Physical Chemistry>Chemical Thermodynamics>Thermochemistry

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})

MEDIUM

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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:

MEDIUM

Chemistry>Physical Chemistry>Chemical Thermodynamics>Thermochemistry

For the reaction:

X_{2} {O_{4}}_{(l)} \to 2 X {O_{2}}_{(g)}

∆ U = 2 .1 kcal, ∆ S = 20 cal K^{- 1}

300 K

Hence,

∆ G

is:

HARD

Chemistry>Physical Chemistry>Chemical Thermodynamics>Thermochemistry

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)

EASY

Chemistry>Physical Chemistry>Chemical Thermodynamics>Thermochemistry

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}

)

MEDIUM

Chemistry>Physical Chemistry>Chemical Thermodynamics>Thermochemistry

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:

HARD

Chemistry>Physical Chemistry>Chemical Thermodynamics>Thermochemistry

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:

MEDIUM

Chemistry>Physical Chemistry>Chemical Thermodynamics>Thermochemistry

Enthalpy of sublimation of iodine is

24 c a l g^{- 1}

200 ° C

. If specific heat of

I_{2}

(s) and

I_{2}

(vap) are

0.055

and

0.031 c a l g^{- 1} K^{- 1}

respectively, then enthalpy of sublimation of iodine at

250 ° C

c a l g^{- 1}

is:

MEDIUM

Chemistry>Physical Chemistry>Chemical Thermodynamics>Thermochemistry

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>Chemical Thermodynamics>Thermochemistry

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>Chemical Thermodynamics>Thermochemistry

The heat of combustion of ethanol into carbon dioxide and water is

- 327

Kcal at constant pressure. The heat evolved (in cal) at constant volume at

27 ° C

(if all gases behave ideally) is

(R = 2 cal {mol}^{- 1} K^{- 1})

________

EASY

Chemistry>Physical Chemistry>Chemical Thermodynamics>Thermochemistry

The reaction in which

ΔH > ΔU

EASY

Chemistry>Physical Chemistry>Chemical Thermodynamics>Thermochemistry

For a reaction,

A (g) \to A (l); ΔH = - 3 RT .

The correct statement for the reaction is

EASY

Chemistry>Physical Chemistry>Chemical Thermodynamics>Thermochemistry

Identify the INVALID equation.

HARD

Chemistry>Physical Chemistry>Chemical Thermodynamics>Thermochemistry

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

)

Which of the following statements is correct about the heat of combustion?

Important Questions on Chemical Thermodynamics

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