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

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Enthalpy $(H)$ of system is equal to

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Important Questions on Thermodynamics

MEDIUM

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

When $0.8 g$ of glucose, $C_{6} H_{12} O_{6}$ , was burnt in a bomb calorimeter, according to the following equation, the temperature raise is found to be $2 K$ at $1 atm$ .

$C_{6} H_{12} O_{6 (s)} + 6 O_{2 (g)} ⟶ 6 {CO}_{2 (g)} + 6 H_{2} O_{(l)}$

If the heat capacity of the bomb calorimeter is $6.8 kJ K^{- 1}$ , the approximate enthalpy change of the reaction in $kJ {mol}^{- 1}$ is (Molar mass of glucose $= 180 g {mol}^{- 1}$ )

MEDIUM

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

At standard conditions, if the change in the enthalpy for the following reaction is $- 109 {kJmol}^{- 1}$

$H_{2 (g)} + {Br}_{2 (g)} \to 2 {HBr}_{(g)}$

Given that bond energy of $H_{2}$ and ${Br}_{2}$ is $435 {kJmol}^{- 1}$ and $192 {kJmol}^{- 1}$ , respectively, what is the bond energy (in $kJ {mol}^{- 1}$ ) of $HBr ?$

EASY

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

The heat of reaction for

$C_{10} H_{8} (s) + 12 O_{2} (g) ⟶ 10 {CO}_{2} (g) + 4 H_{2} O (l)$ at constant volume is $- 1228.2 kcal$ at $25^{0} C$ . The heat of reaction at constant pressure and same temperature is

EASY

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

The bond dissociation enthalpy of gaseous

H_{2}, {Cl}_{2}

and

HCl

are

435.243

and

431 kJ {mol}^{- 1}

respectively. In the same unit, enthalpy of formation of

HCl

gas is

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

Standard molar enthalpies of formation of

{CaCo}_{3} (s), Ca ω (s);

and

{Co}_{2} (g)

are

- 1206.92 KJ {mol}^{- 1}, - 635.09 KJ {mol}^{- 1}

and

- 393.51

respectively. The

Δ

Hr for decomposition of

Ca {CO}_{3} (s)

MEDIUM

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

For the reaction

$N_{2} O_{4} (g) ⟶ 2 {NO}_{2} (g)$

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?

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 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:

EASY

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

Which one among the following is the correct option for right relationship between

C_{p}

and

C_{v}

for one mole of ideal gas?

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

25 ° C

and

1 atm

pressure, the enthalpy of combustion of benzene

(l)

and acetylene

(g)

are

- 3268 kJ {mol}^{- 1}

and

- 1300 kJ {mol}^{- 1}

, respectively. The change in enthalpy for the reaction

3 C_{2} H_{2} (g) \to C_{6} H_{6} (l)

, is

EASY

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

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>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

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

EASY

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

For which of the following reactions,

∆ H

is equal to

∆ U

EASY

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

The reaction in which

ΔH > ΔU

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})

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:

Enthalpy (H) of system is equal to

Important Questions on Thermodynamics

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Enthalpy $(H)$ of system is equal to