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 lattice energy born-haber cycle born-haber cycles energy cycles

The Born Haber cycle below represents the energy changes occurring at 298K when KH is formed from its elements
v : ${ \Delta H } { atomisation }$ K = 90 kJ/mol
w : ${ \Delta H } _{ ionisation }$ K = 418 kJ/mol
x : ${ \Delta H } _{ dissociation }$ H = 436 kJ/mol
y : ${ \Delta H } _{ electron affinity }$ H = 78 kJ/mol
z : ${ \Delta H } _{ lattice }$ KH = 710 kJ/mol

In terms of the letters v to z the expression for
${ \Delta H } _{ electron affinity }$ of H is ${ \Delta H } _{ electron affinity }$  is _.
I

  1. $y$
  2. $y/2$
  3. $2y$
  4. $y/3$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
The electron affinity $\Delta { H } _{ electron\: affinity }$  of an atom or molecule is defined as the amount of energy  released when an electron is added to a neutral atom or molecule in the gaseous state to form a negative ion. It is exothermic as heat energy is released from the system.

$\Delta { H } _{ electron\: affinity }$ should be y not y/2.
Multiple choice chemistry lattice energy born-haber cycle born-haber cycles energy cycles

The energy change for the alternating reaction that yields chlorine sodium $(Cl^{+}Na^{-})$ will be:

$2Na(s)\, +\, Cl _2(g)\,\rightarrow\, 2Cl^{+}Na^{-}(s)$

Given that:

Lattice energy of $NaCl\,=\,-787\, kJ\,mol^{-1}$

Electron affinity of $Na\,=\,-52.9\, kJ\, mol^{-1}$

Ionisation energy of $Cl\, =\, +\,1251\, kJ\, mol^{-1}$

BE of $Cl _2\,=\,244\, kJ\, mol^{-1}$

Heat of sublimation of $Na(s)\, =\,107.3\, kJ\, mol^{-1}$

$\Delta H _f(NaCl)\, =\,-411\, kJ\, mol^{-1}$.

  1. +640 kJ

  2. +1280 kJ

  3. -410 kJ

  4. +410 kJ
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The Born-Haber cycle for the formation of 2Cl+Na- involves sublimation of Na, dissociation of Cl2, ionization of Cl, electron affinity of Na, and lattice energy. Summing these steps to match the formation enthalpy of 2 units of the product gives the energy change.

Multiple choice chemistry lattice energy born-haber cycle born-haber cycles energy cycles

The lattice energy of NaCl(s) using the following data will be:

heat of sublimation of $Na(s)\,=\,S$

$(IE) _1$ of $Na\,(g)\,=\,I$

bond dissociation energy of $Cl _2\,(g)\,=\,D$

electron affinity of $Cl\,(g)\,=\,-E$

heat of formation of $NaCl(s)\,=\,-Q$

  1. Lattice energy $-U\, =\, S\, +\, I\, +\,\displaystyle \frac{D}{2}\, -\, E\, -\,Q$
  2. Lattice energy $-U\, =\, S\, -\, I\, +\,\displaystyle \frac{D}{2}\, -\, E\, -\,Q$
  3. Lattice energy $-U\, =\, S\, +\, I\, +\,\displaystyle \frac{D}{2}\, +\, E\, -\,Q$
  4. Lattice energy $-U\, =\, S\, -\, I\, -\,\displaystyle \frac{D}{2}\, +\, E\, +\,Q$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

An estimate of the strength of the bonds in an ionic compound can be obtained by measuring the lattice energy of the compound, which is the energy given off when oppositely charged ions in the gas phase come together to form a solid.

The Lattice energy of NaCl from its elements Sodium and Chlorine in their stable forms is modeled in five steps in the diagram:

  1. Enthalpy change of atomization enthalpy of lithium
  2. Ionization enthalpy of lithium
  3. Atomization enthalpy of fluorine
  4. Electron affinity of fluorine
  5. Lattice enthalpy
$-U\, =\, S\, +\, I\, +\,\displaystyle \frac{D}{2}\, -\, E\, -\,Q$

Multiple choice chemistry lattice energy born-haber cycle born-haber cycles energy cycles

Use the following data to calculate second electron ainity of oxygen, i.e., for the process
$O^{-}(g) + e^{-}(g)  \rightarrow O^{2-}(g)$
Is the $O^{2-}$ ion stable in the gas phase?.Why is it stable in solid MgO?
Heat of sublimation of $Mg(s) = + 147.7 kJ mol^{-1}$
Ionisation energy of Mg(g) to form
$Mg^{2+}(g) = + 2189.0 kJ mol^{-1}$
Bond dissociation energy for $O _2 = + 498.4 kJmol^{-1}$
First electron affinity of $O(g) = - 141.0 kJ mol^{-1}$
Heat formation of $MgO(s) = -601.7 kJ mol^{-1}$
Lattice energy of $MgO = -3791.0 kJ mol^{-1}$

  1. 601.7

  2. 744.4

  3. 1346.1

  4. 147.7
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Option (B) is correct.

$\triangle H _1=-1346.1+q\ Mg(s)+\frac { 1 }{ 2 } O _{ 2 }(g)\rightarrow MgO(s)\ \triangle H _{ 2 }=-601.7\ By\quad Born-Haber\quad Cycle(based\quad on\quad Hess\quad law)\ \triangle H _{ 1 }=\triangle H _{ 2 }\ -1346.1+q=-601.7\ \qquad \qquad q=744.4kJ\quad mol^{-1}$

Multiple choice chemistry lattice energy born-haber cycle born-haber cycles energy cycles

Caesium chloride is formed according to the following equation:

$Cs(s)+0.5{Cl} _{2}(g)\longrightarrow CsCl(s)$

The enthalpy of sublimation of $Cs$, enthalpy of dissociation of chlorine, ionization energy of $Cs$ and electron affinity of chlorine are $81.2, 243.0, 375.7$ and $-348.3kJ$ ${ol}^{-1}$. The energy change involved in the formation of $CsCl$ is $388.6\ kJ.{mol}^{-1}$. Calculate the lattice energy of $CsCl$.

  1. $-618.7\ kJ{mol}^{-1}$
  2. $+618.7\ kJ{mol}^{-1}$
  3. $1315.2\ kJ{mol}^{-1}$

  4. None of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Multiple choice chemistry lattice energy born-haber cycle born-haber cycles energy cycles

Standard enthalpy of formation $(\Delta H _f)$ of which of the following is zero at $25^0C$ ?

  1. White phosphorous

  2. Red phosphorous
  3. Red lead $(Pb _3O _4)$
  4. $H^+(g)$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

White phosphors is the elemental form of phosphorus for which enthalpy of formation is zero, while, $H^+$ and $Pb _3O _4$ are not elemental forms.

Multiple choice chemistry lattice energy born-haber cycle born-haber cycles energy cycles

The enthalpy of hydrogenation for $1-pentene$ is $+126\ kJ/mol$. The enthalpy of hydrogenation for $1, 3-pentadiene$ is $+230\ kJ/mol$. Hence estimate the resonance magnitude of (delocalization) energy of $1, 3-pentadiene$.

  1. $22\, kJ/mol$
  2. $104\, kJ/mol$
  3. $252\, kJ/mol$

  4. cannot be calculated from this information
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Enthalpy of hydrogenation per bond$=+126\ kJ/mol$


Enthalpy of hydrogenation for 2 bonds$=+252\ kJ/mol$


Resonance energy$=252-230=22\ kJ/mol$

Multiple choice chemistry lattice energy born-haber cycle born-haber cycles energy cycles

The heats of neutralization of $CH _3COOH.HCOOH, HCN$ and $HClO$ are 13.2, 13.4,2.9 and 3.6 kcal/eq respectively. Then, the degree of hydrolysis for the respective ions will be in the order :

  1. $CH _3COO^- < HCOO^- < CN^- < ClO^-$
  2. $HCOO^- < ClO^- < CN^- < CH _3COO^-$
  3. $CH _3COO^- < CN^- < ClO^- < HCOO^-$
  4. $HCOO^- < CH _3COO^- < ClO^- < CN^-$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Strong acid have high heat of neutralization and are very much stable so required high energy for dissociation. Hence, weak acids are hydrolysed at faster rate than strong acids.

Multiple choice biology health and hygiene - food for living energy from different food components nutritional requirements of the body need for nutrients

Energy value per gram of alcohol is

  1. $4\ kcal$
  2. $4.3\ kcal$
  3. $9.3\ kcal$
  4. $7.1\ kcal$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Just like any food or drink, alcoholic drinks contain energy or calories. There are 7 calories per gram of alcohol (29kJ). A 'standard' alcoholic drink or 'unit' contains 8 grams of alcohol, which is equal to 56 calories from the alcohol alone. 

So, the correct answer is '7.1 kcal'.

Multiple choice chemistry lattice energy defining lattice energy ionic or electrovalent bond energy cycles

From the following sequence calculate the lattice energy of AB(s):
$A(s)\rightarrow A(g)+e$;      $610\;kJ\;mol^{-1}$
$B(g)+e\rightarrow B(g);$      $-260\;kJ\;mol^{-1}$
$A(s)+B(g)\rightarrow AB(s);$      $-569\;kJ\;mol^{-1}$

  1. $-219$
  2. $-919$
  3. $+1539$
  4. $+301$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
The lattice energy of a crystalline solid is usually defined as the energy of formation of the crystal from infinitely-separated ions, molecules, or atoms. 
let the equations be 1, 2 and 3.
We will get the lattice energy by  $3-2-1 $= $-569+260-610$ $= -919$
Multiple choice physics heat - measurement application of various thermometric scales different types of thermometers measuring temperature introduction to temperature

$\begin{array} { l } { \text { Energy required to dissociate } 4 \mathrm { g } \text { of gaseous } } \ { \text { hydrogen into free gaseous atoms is } 208 \mathrm { Kcal {at}  }  } \ {  25 ^ { \circ } \mathrm { C } \text { . The bond energy of } \mathrm { H } - \mathrm { H } \text { bond will be : } } \end{array}$ .

  1. $1.04Kcal$
  2. $10.4Kcal$
  3. $104Kcal$
  4. $1040Kcal$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
Given heat of atmosphere $40=260\ Kcal$
$2H _{2} \rightarrow 4H$
$\triangle H = 208\ Kcal$
$20 \rightarrow 1\ mole$
$40 \rightarrow 2 \ mole$
$Hene \ 2 H-H$ bonds area brown $bg $
$20\ kcal $ energy so in order to break $1\ H-H$ bound we required $\dfrac{208}{2}= 104\ Kcal$
Hence the bond energy of $H-H$ bound will be $=104\ kcal$
Multiple choice biology food and human health balanced diet and malnutrition balanced and unbalanced food digestive disorders diseases caused by changes in lifestyle diseases and toxic substance health and its maintenance

Kilocalories of usable energy liberated by one mole of glucose is?

  1. $80$
  2. $160$
  3. $180$
  4. $380$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The aerobic respiration of one mole of glucose typically yields approximately 38 ATP. Given that the hydrolysis of one mole of ATP releases roughly 10 kcal, the total energy is approximately 380 kcal.

Multiple choice chemistry introduction to organic chemistry bonding in organic molecule tetravalence of carbon: shapes of organic compounds introduction to carbon and its compounds

The enthalpy of reaction,${\text{2HC}} \equiv {\text{CH + 5C}}{{\text{O}} _{\text{2}}}{\text{ + 2}}{{\text{H}} _{\text{2}}}{\text{O}}\,$
 If the bounds energies of ${\text{C - H,C}} \equiv {\text{C,}}\,{\text{O = O,C = O}}$ abd ${\text{O - H}}$ bounds are p,q,r,s,t respectively 

  1. $\left[ {8s + 4t} \right] - \left[ {4p + q + 5r} \right]$
  2. $\left[ {4p + 2q + 5r} \right] - \left[ {8s + 4t} \right]$
  3. $\left[ {4p + 2q + 5r + 8s + 4t} \right]$
  4. $\left[ {2q + q + 5r + } \right] - \left[ {8s + 4t} \right]$
Reveal answer Fill a bubble to check yourself
A Correct answer