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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What is the value of change in internal energy at 1 atm in the process

$H_{2} O (l, 323 K) ⟶ H_{2} O (g, 423 K)$

Given: $C_{V, m} (H_{2} O, l) = 75 \cdot 0 {JK}^{- 1} {mol}^{- 1}$ ; $C_{P, m} (H_{2} O, g) = 33 \cdot 314 {JK}^{- 1} {mol}^{- 1}$

$Δ H_{vap}$ at 373 K = 40.7 kJ/mol

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Important Questions on Thermodynamics

HARD

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

Nitroglycerine $(MW = 227.1)$ detonates according to the following equations,

$2 C_{3} H_{5} {({NO}_{3})}_{3} (l) ⟶ 3 N_{2} (g) + \frac{1}{2} O_{2} (g) + 6 {CO}_{2} (g) + 5 H_{2} O (g)$

The standard molar enthalpies of formation, ${ΔH}_{f} °$ for all the compounds are given below.

${ΔH}_{f} ° [C_{3} H_{5} {({NO}_{3})}_{3}] = - 364 kJ / mol$
${ΔH}_{f} ° [{CO}_{2} (g)] = - 393.5 kJ / mol$
${ΔH}_{f} ° [H_{2} O (g)] = - 241.8 kJ / mol$
${ΔH}_{f} ° [N_{2} (g)] = 0 kJ / mol$
${ΔH}_{f} ° [O_{2} (g)] = 0 kJ / mol$

The enthalpy change when $10 g$ of nitroglycerine is detonated is

MEDIUM

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

For the reaction

$N_{2} O_{4} (g) ⟶ 2 {NO}_{2} (g)$

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

If the standard molar enthalpy change for combustion of graphite powder is

- 2.48 \times 10^{2} kJ {mol}^{- 1}

, the amount of heat generated on combustion of

1 g

of graphite powder in

kJ

(Nearest integer):

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

The standard heat of formation of

{CH}_{4}, {CO}_{2}

and

H_{2} O

are

- 762, - 394.8

and

- 285.82 kJ {mol}^{- 1},

respectively. Heat of vaporisation of water is

44 kJ {mol}^{- 1} .

Calculate the amount of heat eveolved when

22.4 L

{CH}_{4},

kept under normal conditions, is oxidized into its gaseous products.

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

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

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

17.0 g

{NH}_{3}

completely vapourises at

- 33.42 ° C

and

1

bar pressure and the enthalpy change in the process is

23.4 kJ {mol}^{- 1}

. The enthalpy change for the vapourisation of

85 g

{NH}_{3}

under the same conditions is

kJ

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

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

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)

EASY

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

For which of the following reactions,

∆ H

is equal to

∆ U

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 reaction in which

ΔH > ΔU

HARD

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

Tin is obtained from cassiterite by reduction with coke. Use the data given below to determine the minimum temperature (in $K$ ) at which the reduction of cassiterite by coke would take place.

$298 K : Δ_{f} H^{0} ({SnO}_{2} (s)) = - 581.0 kJ {mol}^{- 1}, Δ_{f} H^{0} ({CO}_{2} (g)) = - 394.0 kJ {mol}^{- 1}$

$S^{0} ({SnO}_{2} (s)) = 56.0 {JK}^{- 1} {mol}^{- 1}, S^{0} (Sn (s)) = 52.0 {JK}^{- 1} {mol}^{- 1}$

$S^{0} (C (s)) = 6.0 {JK}^{- 1} {mol}^{- 1}, S^{0} ({CO}_{2} (g)) = 210.0 {JK}^{- 1} {mol}^{- 1}$

Assume that the enthalpies and the entropies are temperature independent.

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

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:

What is the value of change in internal energy at 1 atm in the process H 2 O l⁡ , 3 2 3 K ⟶ H 2 O g , 4 2 3 K Given: C V , m H 2 O , l⁡ = 7 5 · 0 JK - 1 mol - 1 ; C P , m H 2 O , g = 3 3 · 3 1 4 JK - 1 mol - 1 Δ H vap at 373 K = 40.7 kJ/mol

Important Questions on Thermodynamics

Learn and Prepare for any exam you want !

What is the value of change in internal energy at 1 atm in the process

$H_{2} O (l, 323 K) ⟶ H_{2} O (g, 423 K)$

Given: $C_{V, m} (H_{2} O, l) = 75 \cdot 0 {JK}^{- 1} {mol}^{- 1}$ ; $C_{P, m} (H_{2} O, g) = 33 \cdot 314 {JK}^{- 1} {mol}^{- 1}$

$Δ H_{vap}$ at 373 K = 40.7 kJ/mol