MEDIUM

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The following two reactions are known:

$\begin{array}{l} {Fe}_{2} O_{3} (s) + 3 CO (g) \overset{}{\to} 2 Fe (s) + 3 {CO}_{2} (g) . .. (1) \\ ΔH = - 26 .8 kJ \\ {Fe}_{2} O (s) + CO (g) \overset{}{\to} Fe (s) + {CO}_{2} (g); . .. (2) \\ ΔH = - 16 .5 kJ \end{array}$

The value of $ΔH$ for the following reaction

${Fe}_{2} O_{3} (s) + CO (g) \overset{}{\to} 2 FeO (s) + {CO}_{2} (g) is;$

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Important Questions on Thermodynamics

MEDIUM

Chemistry>Physical Chemistry>Thermodynamics>Hess's Law of Constant Heat Summation

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

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

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

EASY

Chemistry>Physical Chemistry>Thermodynamics>Hess's Law of Constant Heat Summation

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?

MEDIUM

Chemistry>Physical Chemistry>Thermodynamics>Hess's Law of Constant Heat Summation

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:

EASY

Chemistry>Physical Chemistry>Thermodynamics>Hess's Law of Constant Heat Summation

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

EASY

Chemistry>Physical Chemistry>Thermodynamics>Hess's Law of Constant Heat Summation

For which of the following reactions,

∆ H

is equal to

∆ U

EASY

Chemistry>Physical Chemistry>Thermodynamics>Hess's Law of Constant Heat Summation

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>Hess's Law of Constant Heat Summation

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})

HARD

Chemistry>Physical Chemistry>Thermodynamics>Hess's Law of Constant Heat Summation

When

600 mL

0.2 M {HNO}_{3}

is mixed with

400 mL

0.1 M NaOH

solution in a flask, the rise in temperature of the flask is_____

\times 10^{- 2} ° C

(Enthalpy of neutralisation

= 57 kJ {mol}^{- 1}

and Specific heat of water

= 4.2 {JK}^{- 1} g^{- 1}

) (Neglect heat capacity of flask)

EASY

Chemistry>Physical Chemistry>Thermodynamics>Hess's Law of Constant Heat Summation

Identify the INVALID equation.

HARD

Chemistry>Physical Chemistry>Thermodynamics>Hess's Law of Constant Heat Summation

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>Hess's Law of Constant Heat Summation

The elements with the highest and the lowest enthalpy of atomisation respectively, for first row transition elements are:

HARD

Chemistry>Physical Chemistry>Thermodynamics>Hess's Law of Constant Heat Summation

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>Hess's Law of Constant Heat Summation

For one mole of NaCl(s) the lattice enthalpy is

${Na}_{(s)} + \frac{1}{2} {Cl}_{2} (g) \overset{+ 108.4 kJ / mol}{⟶} {Na}_{(s)} + \frac{1}{2} {Cl}_{2} (g) \overset{+ 495.6 kJ / mol}{⟶} {Na}_{(g)}^{+} + \frac{1}{2} {Cl}_{2} (g) \overset{121 kJ / mol}{⟶}$

${Na}_{(g)}^{+} + Cl (g) \overset{- 348.6 kJ / mol}{⟶} {Na}_{(g)}^{+} + {Cl}_{(g)}^{-} \overset{{ΔH}^{0} altice}{⟶} Nacl$ (solid) $\underset{- 411.2 kJ / mol}{\leftarrow} {Na}_{(s)} + \frac{1}{2} {Cl}_{2} (g)$

HARD

Chemistry>Physical Chemistry>Thermodynamics>Hess's Law of Constant Heat Summation

When 100 mL of 1.0 M HCl was mixed with 100 mL of 1.0 M NaOH in an insulated beaker at constant pressure, a temperature increase of

{5.7}^{o} C

was measured for the beaker and its contents (Expt.1). Because the enthalpy of neutralization of a strong acid with a strong base is a constant

(- 57.0 k J m o l^{- 1})

, this experiment could be used to measure the calorimeter constant. In a second experiment (Expt. 2), 100 mL of 2.0 M acetic acid

(K_{a} = 2.0 \times 10^{- 5})

was mixed with 100 mL of 1.0 M NaOH (under identical conditions to Expt. 1) where a temperature rise of

{5.6}^{o} C

was measured. (Consider heat capacity of all solutions as

4.2 J g^{- 1} K^{- 1}

and density of all solutions as

1.0 g m L^{- 1}

)

Enthalpy of dissociation

(i n k J m o l^{- 1})

of acetic acid obtained from the Expt. 2 is

MEDIUM

Chemistry>Physical Chemistry>Thermodynamics>Hess's Law of Constant Heat Summation

The ionization enthalpy of

{Na}^{+}

formation from

{Na}_{(g)}

495.8 kJ {mol}^{- 1},

while the electron gain enthalpy of

Br

- 325.0 kJ {mol}^{- 1}

. Given the lattice enthalpy of

NaBr

- 728.4 kJ {mol}^{- 1}

. The energy for the formation of

NaBr

ionic solid is

(-)_____10^{- 1} kJ {mol}^{- 1}

HARD

Chemistry>Physical Chemistry>Thermodynamics>Hess's Law of Constant Heat Summation

The Born-Haber cycle for $KCl$ is evaluated with the following data:
$Δ_{f} H^{Θ} for KCl = - 436.7 {kJmol}^{- 1}; Δ_{sub} H^{Θ} for K = 89.2 {kJmol}^{- 1};$

$Δ_{ionization} H^{Θ} for K = 419.0 kJ {mol}^{- 1}; Δ_{electron gain} H^{Θ} for {Cl}_{(g)} = - 348.6 {kJmol}^{- 1}$

$Δ_{bond} H^{Θ} for {Cl}_{2} = 243.0 {kJmol}^{- 1}$
The magnitude of lattice enthalpy of $KCl$ in ${kJmol}^{- 1}$ is (Nearest integer)

MEDIUM

Chemistry>Physical Chemistry>Thermodynamics>Hess's Law of Constant Heat Summation

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>Thermodynamics>Hess's Law of Constant Heat Summation

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>Hess's Law of Constant Heat Summation

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>Hess's Law of Constant Heat Summation

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}

The following two reactions are known: Fe2O3(s)+3CO(g)→2Fe(s)+3CO2(g) ...(1) ΔH=−26.8 kJFe2O(s)+CO(g)→Fe(s)+CO2(g); ...(2) ΔH=−16.5 kJ The value of ΔH for the following reaction Fe2O3(s)+CO(g)→2FeO(s)+CO2(g) is;

Important Questions on Thermodynamics

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