Chemistry

Thermochemistry and Equilibrium

121 Questions

Thermochemistry and equilibrium problems focus on calculating bond energies, lattice enthalpy, and the Born Haber cycle. These concepts are vital for scoring well in chemistry sections. Regular practice ensures a clear understanding of energy changes in reactions.

Bond energy calculationsBorn Haber cycleLattice enthalpyEnthalpy of solutionThermochemical equations

Thermochemistry and Equilibrium Questions

Multiple choice chemistry energetics and thermochemistry bond energies and enthalpy changes bond enthalpies enthalpies for different types of reactions

The bond energy of $H _2$ is $104.3 : kcal : mol^{-1}$. It means that:

  1. 104.3 kcal heat is needed to break up $'\! N'$ bonds in $N$ moleules of $H _2$
  2. 104.3 kcal heat is needed to break up $6.023\times 10^{23}$ molecules into $1.2046\times 10^{24}$ of H
  3. 104.3 kcal heat is evolved during combination of $2N$ atoms of H to form $N$ molecules of $H _2$

  4. All of the above
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Bond energy is defined as the energy required to break one mole of bonds in the gaseous state. This is equivalent to the energy released when one mole of bonds is formed from gaseous atoms.

Multiple choice chemistry energetics and thermochemistry bond energies and enthalpy changes bond enthalpies enthalpies for different types of reactions

The average, $S - F$ bond energy in $SF _6$ if the $\Delta H^{\circ} _f$ value are $-1100, +275$ and $+80 kJ/mol$ respectively for $SF _6(g),$ S(g) and F(g) is

  1. $390.1 kJ/mol$
  2. $103.9 kJ/mol$
  3. $903.1 kJ/mol$
  4. $309.1 kJ/mol$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
As we know,
Heat of a reaction = Bond energy of reactants - Bond energy of products
here,
$S(s) +3F _2(g) \rightarrow SF _6(g)$
so heat of reaction = 
$-1100 = 275 + 6*80$ - bond energy of $SF _6$ 
bond energy of $SF _6$ $= 1855$
so bond energy of $S-F = 1855/6 = 309.1 kJ/mol$
Multiple choice chemistry energetics and thermochemistry bond energies and enthalpy changes bond enthalpies enthalpies for different types of reactions

Bond energy of hydrogen gas is $-433 kJ$. How much is the bond dissociation energy of $0.5 mole$ of hydrogen gas?

  1. $-433 kJ$
  2. $+433 kJ$
  3. $-216 kJ$
  4. $+216 kJ$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Bond dissociation energy $= -$ bond formation energy
Given, bond energy of hydrogen $= -433 kJ$
$\therefore$ Bond dissociation energy of one mole ${ H } _{ 2 } = 433 kJ$
$\therefore$ Bond dissociation energy of $0.5$ mole ${ H } _{ 2 }=\dfrac { 433 }{ 2 } =+216.5kJ$

Multiple choice chemistry energetics and thermochemistry bond energies and enthalpy changes bond enthalpies enthalpies for different types of reactions

Enthalpy of polymerisation of ethylene, as represented by the reaction, $ nCH _2 = CH _2 \rightarrow {(-CH _2- CH _2-)} _n   $ is -100kJ per mole of ethylene.Given bond enthalpy of $ C = C $ bond is 600 kJ$ mol^{-1} $ , enthalpy of $ C - C $ bond (in kJ mol) will be :

  1. 2940 kcal $ mol^{-1} $
  2. 350 kJ $ mol^{-1} $
  3. 700 kJ $ mol^{-1} $
  4. 1470 kcal $ mol^{-1} $
Reveal answer Fill a bubble to check yourself
B,D Correct answer
Explanation

$ nCH _2 = CH _2 \rightarrow (-CH _2 - CH _2- ) _n    \Delta H $= 100 KJ/mole
Double bond of ethylene converted to two single bonds.
$ \Delta H $ = - 100 =$ B.E. _{C=C} - 2 B.E. _{C-C}$ 
$ \implies $ - 100 = 600 - $ 2 \times B.E. _{C-C} \implies B.E. _{C-C}$ = 350 KJ/mole = 1470kcal$mol^{-1}$

Multiple choice chemistry energetics and thermochemistry bond energies and enthalpy changes bond enthalpies enthalpies for different types of reactions

$\triangle H _{f} (C _{2}H _{4}) = 12.5\ kcal$

Heat of atomisation of $C = 171\ kcal$
Bond energy of $H _{2} = 104.3\ kcal$
Bond energy $C - H = 99.3\ kcal$

What is $C = C$ bond energy?

  1. $140.9\ kcal$
  2. $49\ kcal$
  3. $40\ kcal$
  4. $76\ kcal$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

C2H4 formation: 2C(s) + 2H2(g) → C2H4; ΔfH = 12.5 kcal. Atomization: 2C(s) → 2C(g); ΔH = 2(171) = 342 kcal. 2H2(g) → 4H(g); ΔH = 2(104.3) = 208.6 kcal. Total atomization = 550.6 kcal. This forms 4 C-H bonds (4×99.3 = 397.2) and 1 C=C bond. BE(C=C) = 550.6 - 397.2 - 12.5 = 140.9 kcal.

Multiple choice chemistry energetics and thermochemistry bond energies and enthalpy changes bond enthalpies enthalpies for different types of reactions
$\overset { \underset { | }{ H }  }{ \underset { \overset { | }{ H }  }{ C }  }=\overset { \underset { | }{ H }  }{ \underset { \overset { | }{ H }  }{ C }  } +H-H\rightarrow H-\overset { \underset { | }{ H }  }{ \underset { \overset { | }{ H }  }{ C }  } -\overset { \underset { | }{ H }  }{ \underset { \overset { | }{ H }  }{ C }  } -H $

From the following bond energies:

$H - H$ bond energy : $431.37\ kJ\ mol^{-1}$

$C = C$ bond energy : $606.10\ kJ\ mol^{-1}$

$C - C$ bond energy : $336.49\ kJ\ mol^{-1}$

$C - H$ bond energy : $410.50\ kJ\ mol^{-1}$

Enthalpy for the reactions, will be?
  1. $+553.0\ kJ\ mol^{-1}$
  2. $+1523.6\ kJ\ mol^{-1}$
  3. $-243.6\ kJ\ mol^{-1}$
  4. $-120.0\ kJ\ mol^{-1}$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Delta H = Sum(BE reactants) - Sum(BE products). Reactants: 1(C=C) + 4(C-H) + 1(H-H) = 606.1 + 4(410.5) + 431.37 = 606.1 + 1642 + 431.37 = 2679.47. Products: 1(C-C) + 6(C-H) = 336.49 + 6(410.5) = 336.49 + 2463 = 2799.49. Delta H = 2679.47 - 2799.49 = -120.02 kJ/mol.

Multiple choice chemistry energetics and thermochemistry bond energies and enthalpy changes bond enthalpies enthalpies for different types of reactions

Dissociation of water takes place in two steps:
$H _2O \rightarrow H^+ + OH^-$; $\Delta H$ = +497.8 kJ
$OH^- \rightarrow H^+ + O^{2-}$; $\Delta H$ = +428.5 kJ
What is the bond energy of O - H bond?

  1. 463.15 kJ $mol^{-1}$
  2. 428.5 kJ $mol^{-1}$
  3. 69.3 kJ $mol^{-1}$
  4. 926.3 kJ $mol^{-1}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In given 2 reactions, $\Delta H$ is basically representing bond energies of H-O bond. So, our answer should be average of these two $\Delta H$ values.
Hence, Average of two bond dissociation energies:    $\frac{497.8 + 428.5}{2}$ = 463.15kJ $mol^{-1}$

Multiple choice chemistry hard water and soft water heavy water study of heavy water hydrogen and its compounds

If a mole of hydrogen molecule is heated to a high temoerature then which of the following reactions take place?

  1. $H _2{(g)} + 436 kJ mol^{-1} \rightarrow H{(g)} + H{(g)}$
  2. $2H2{(g)} + 820 kJ mol^{-1} \rightarrow 2H _2{(g)}$
  3. $H _2{(g)} + H _2{(g)} + 436kJ mol^{-1} \rightarrow H^{+} _{(aq)} + H^{-} _{(aq)}$
  4. $H _2{(g)} + 200kJ mol^{-1} \rightarrow H _{(g)} + H _{(g)}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The amount of energy required to break $H-H$ bond of 1 mole of gaseous hydrogen is 436 $kJ \ mol^{-1}$. This is known as bond dissociation enthalpy.
$H _2{(g)} + 436 \  kJ mol^{-1} \rightarrow  H{(g)} + H{(g)}$

Multiple choice biology coal, petroleum and petrochemicals carbon cycling mineral coal carbon cycle coal and its products

The calorific value of lignite is about _____ kJ/g.

  1. 90

  2. 78

  3. 87

  4. 8

Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The calorific value of the fuel is also called as the heat value of the fuel. It is defined as the amount of heat released by burning of unit quantity of the fuel. The calorific value is an important characteristic of the fuel. The unit of measurement of the calorific value is the same as the energy.

plant coal have a Calorific Value in the range of 9500 kJ/kg to 27000 kJ/ kg i.e 95 to 27 KJ/gm
The calorific value ranges from 8000 kJ/kg to 15000 kJ/kg i.e 8 to 15 KJ/gm.

Multiple choice biology food and it's constituents energy giving food carbohydrate and its test biological molecules

The energy produced by 1g of carbohydrate is

  1. 4.8 cal

  2. 4.2 kcal

  3. 9 joules

  4. 9.2 kcal
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
Carbohydrates, proteins and fats in the foods provide energy for the body functions and physical activities. They, however, do not have same energy content. The following is the energy-content by respective nutrients:
1 gram of carbohydrates- 4kcal
1 gram of protein- 4 kcal
1 gram of fats- 9 kcal
So, the correct answer is '4.2 kcal'
Multiple choice physics quantum physics photons concept of photon photons and photoelectric effect

Approximately, the temperature corresponding to $1 eV$ translational kinetic energy of molecule is

  1. $7.6 \times 10 ^ { 2 } \mathrm { K }$
  2. $7.7 \times 10 ^ { 3 } \mathrm { K }$
  3. $7.1 \times 10 ^ { - 2 } \mathrm { K }$
  4. $7.2 \times 10 ^ { 3 } \mathrm { K }$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The translational kinetic energy of a molecule is given by E = (3/2)kT. Setting E = 1 eV = 1.6 * 10^-19 J, we solve for T = (2 * 1.6 * 10^-19) / (3 * 1.38 * 10^-23). This yields approximately 7727 K.

Multiple choice physics heat energy transfers heat and heat transfer heat energy transfer transfer of heat

$\triangle { H }^{ \circ  }$ for reaction: 
${ F } _{ 2 }+2HCI\rightarrow 2HF+{ CI } _{ 2 }$
is equal to -352.8kJ. If $\triangle { H } _{ f }^{ \circ  }$ for HF is -268.3 kJ ${ mol }^{ -1 }$ then ${ \triangle H } _{ f }^{ \circ  }$ of HCI would be:- 

  1. -22 kJ ${ mol }^{ -1 }$
  2. 88.0 kJ ${ mol }^{ -1 }$
  3. 01.0 kJ${ mol }^{ -1 }$

  4. None
Reveal answer Fill a bubble to check yourself
C Correct answer
Multiple choice chemistry chemical thermodynamics system and surroundings introduction to thermodynamics basics of thermodynamics

Bond dissociation enthalphies of ${ H } _{ 2 }\left( g \right) $ and ${ N } _{ 2\left( g \right)  }$ are enthalpy of formation of $N{ H } _{ 3 }\left( g \right) $ is $-46 kJ mol^{-1}$. What is enthalpy of atomization of $N{ H } _{ 3 }\left( g \right) $?

  1. $390.3 kJ mol^{-1}$
  2. $1170.9kJ mol^{-1}$
  3. $590 kJ mol^{-1}$
  4. $720 kJ mol^{-1}$
Reveal answer Fill a bubble to check yourself
B Correct answer