Calculate ΔG ∘ for the reaction, CaF 2 ( s ) ⇌ Ca 2 + ( aq ) + 2 F - ( aq ) . Given that ΔG f ∘ CaF 2 ( s ) = - 1162 kJ / mol ΔG f ∘ Ca 2 + ( aq ) = - 553 . 0 and ΔG f ∘ F - ( aq ) = - 276 . 5 kJ / mol Also, calculate K sp for this reaction at 25 ° C .

(i) Chemical reaction CaF 2 ( s ) ⇋ Ca + 2 ( aq ) + 2 F - ( aq ) ∆ G ∘ is an extensive property and a state function. △ G ° = △ G ° Ca + 2 ( aq ) + 2 △ G ° F - ( aq ) - △ G ° CaF 2 ( s ) = - 553 . 0 + 2 ( - 276 . 5 ) - ( - 1162 ) = - 553 . 0 - 553 . 0 + 1162 △ G ° = 1162 - 1106 = 56 kJ △ G ° = 56 kJ (ii) △ G = △ G ° + RTinQ Q = reaction quotient. K sp = solubility product. At the equilibrium state, Q = K sp , △ G = 0 △ G ° = - 2 . 303 RT log K sp log K sp = - △ G ° 2 . 303 RT = - 56 × 10 3 2 . 303 × 8 . 314 × 298 = - 9 . 814 = - 10 + 0 . 1855 = log 10 - 10 + log 1 . 55 log K sp = log ( 1 . 55 × 10 - 10 ) Then, K sp = 1 . 55 × 10 - 10

The following reactions are given with their enthalpy changes, at 25 ° C , N 2 ( g ) + 2 O 2 ( g ) → 2 NO 2 ( g ) ; ΔH = 16 . 18 kcal N 2 ( g ) + 2 O 2 ( g ) → N 2 O 4 ( g ) ; ΔH = 2 . 31 kcal Calculate the enthalpy of dimerization of NO 2 . Can N 2 O 4 be stable with NO 2 at 25 ° C ?

The following reactions are given with their enthalpy changes, at 25 ° C , N 2 ( g ) + 2 O 2 ( g ) → 2 NO 2 ( g ) . . . . . . . . ( 1 ) ; ΔH = 16 . 18 kcal N 2 ( g ) + 2 O 2 ( g ) → N 2 O 4 ( g ) . . . . . . . ( 2 ) ; ΔH = 2 . 31 kcal The enthalpy of dimerization of NO 2 in N 2 O 4 can be determined as follows. Enthalpy is an extensive property. 2 NO 2 ( g ) → N 2 O 4 ( g ) . . . . . . . . . 3 ; ∆ H = ? Equation 3 = Equation 2 - Equation 1 Thus, ∆ H = 2 . 31 - 16 . 18 = - 13 . 87 kcal ( - 13 . 87 kcal , N 2 O 4 is stable only at low temperatures)

HARD

JEE Main

IMPORTANT

Earn 100

The heat of formation of ${Fe}_{2} O_{3}$ is $- 821.32 kJ {mol}^{- 1}$ at $298 K$ and $1 atm$ and that of ${Al}_{2} O_{3}$ is $- 1675.60 kJ {mol}^{- 1}$ under the same condition. Calculate the heat of reaction of reduction of $1$ $mole$ of ${Fe}_{2} O_{3}$ with metallic aluminium.

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Important Questions on Chemical Thermodynamics

HARD

JEE Main

IMPORTANT

Modern Approach to Chemical Calculations>Chapter 14 - Chemical Thermodynamics>PROBLEMS>Q 24

A gas is enclosed in a cylinder with a piston. Weights are added to the piston, giving a total mass of

2.20 kg

. As a result, the gas is compressed and the weights are lowered

0.25 m

. At the same time,

1.50 J

of heat is evolved from the system. What is the change in internal energy of the system? (Take

g = 9.8 m / \sec^{2}

)

HARD

JEE Main

IMPORTANT

Modern Approach to Chemical Calculations>Chapter 14 - Chemical Thermodynamics>PROBLEMS>Q 25

Calculate ${ΔG}^{\circ}$ for the reaction, ${CaF}_{2} (s) ⇌ {Ca}^{2 +} (aq) + 2 F^{-} (aq)$ .

Given that ${ΔG}_{f}^{\circ} ({CaF}_{2} (s)) = - 1162 kJ / mol$

${ΔG}_{f}^{\circ} ({Ca}^{2 +} (aq)) = - 553.0$ and ${ΔG}_{f}^{\circ} (F^{-} (aq)) = - 276.5 kJ / mol$

Also, calculate $K_{sp}$ for this reaction at $25 ° C$ .

HARD

JEE Main

IMPORTANT

Modern Approach to Chemical Calculations>Chapter 14 - Chemical Thermodynamics>PROBLEMS>Q 26

To what temperature must magnesium carbonate be heated to decompose it to $MgO$ and ${CO}_{2}$ at $1 atm$ ?

Given:

	${MgCO}_{3} (s)$	$MgO (s)$	${CO}_{2} (g)$
${ΔH}_{f}^{\circ}$	$- 1112$	$- 601.2$	$- 393.5 kJ$
$S^{\circ}$	$65.9$	$26.9$	$213.7 J / K$

HARD

JEE Main

IMPORTANT

Modern Approach to Chemical Calculations>Chapter 14 - Chemical Thermodynamics>PROBLEMS>Q 27

Predict the direction in which ${ΔG}^{\circ}$ for the equilibrium, $N_{2} (g) + 3 H_{2} (g) ⇌ 2 {NH}_{3} (g); {ΔG}_{298}^{\circ} = - 33.32 kJ$ will change with an increase in the temperature. Calculate $ΔG °$ at $500 ° C$ , assuming that $ΔH$ and $ΔS$ do not change with temperature, that is, ${ΔH}_{298}^{\circ} = {ΔH}_{793}$ and ${ΔS}_{298}^{\circ} = {ΔS}_{793}$ .

${ΔH}^{\circ} = - 92.38 kJ$ and ${ΔS}^{\circ} = - 198.2 J / K$

HARD

JEE Main

IMPORTANT

Modern Approach to Chemical Calculations>Chapter 14 - Chemical Thermodynamics>PROBLEMS>Q 28

A heat pump is used to draw water from a well. The temperature of the water is

15 ° C

and that of the atmosphere is

40 ° C

. If the amount of water drawn is

10 kg

from a depth of

12 m

, calculate the amount of heat supplied to the well.

HARD

JEE Main

IMPORTANT

Modern Approach to Chemical Calculations>Chapter 14 - Chemical Thermodynamics>PROBLEMS>Q 29

The following reactions are given with their enthalpy changes, at $25 ° C$ ,

$N_{2} (g) + 2 O_{2} (g) \to 2 {NO}_{2} (g); ΔH = 16.18 kcal$

$N_{2} (g) + 2 O_{2} (g) \to N_{2} O_{4} (g); ΔH = 2.31 kcal$

Calculate the enthalpy of dimerization of ${NO}_{2}$ . Can $N_{2} O_{4}$ be stable with ${NO}_{2}$ at $25 ° C$ ?

MEDIUM

JEE Main

IMPORTANT

Modern Approach to Chemical Calculations>Chapter 14 - Chemical Thermodynamics>PROBLEMS>Q 30

A system is changed from an initial state to a final state in such a manner that

ΔH = q

. If the same change from the initial to the final state were to be made by a different path, would

ΔH

be the same as that of the first path? Would

q

be the same?

HARD

JEE Main

IMPORTANT

Modern Approach to Chemical Calculations>Chapter 14 - Chemical Thermodynamics>PROBLEMS>Q 31

Two moles of an ideal gas are held by a piston under $10 atm$ pressure at $273 K$ . The pressure is suddenly released to $0.4 atm$ and the gas is allowed to expand isothermally. Calculate $W, q, ΔU$ and $ΔH$ .

[Hint: The gas expands irreversibly]

The heat of formation of Fe2O3 is -821.32 kJ mol-1 at 298 K and 1 atm and that of Al2O3 is -1675.60 kJ mol-1 under the same condition. Calculate the heat of reaction of reduction of 1 mole of Fe2O3 with metallic aluminium.

Important Questions on Chemical Thermodynamics

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The heat of formation of ${Fe}_{2} O_{3}$ is $- 821.32 kJ {mol}^{- 1}$ at $298 K$ and $1 atm$ and that of ${Al}_{2} O_{3}$ is $- 1675.60 kJ {mol}^{- 1}$ under the same condition. Calculate the heat of reaction of reduction of $1$ $mole$ of ${Fe}_{2} O_{3}$ with metallic aluminium.