The chemical bond is formed by the participation of only valence electrons, electrons of the outermost shell, of the atom. Born-Land equation While the hard-sphere model is a useful approximation, it does have some issues. To see this trend for yourself, investigate it with our lattice energy calculator! For example, we can find the lattice energy of CaO\text{CaO}CaO using the following information: Since we can find all of these energies experimentally, this is a surefire way of answering "What is the lattice energy of CaO\text{CaO}CaO?". Hsub of Na = 108 kJ/mol (Heat of sublimation) Solid State Chemistry. Lattice energy is equal to negative Q one times Q. How do we get to know that calcium chloride is an Ionic compound? Answer and Explanation: 1 Become a. and P. Day. To correct for this, Born and Land (yes, the same Born as in the Born-Haber cycle, prolific, we know) proposed an equation to describe this repulsive energy: By adding this correction to the hard-sphere equation, differentiating it with respect to rrr, assuming that at r=r0r=r_0r=r0 the potential energy is at a minimum, rearranging for BBB, and finally substituting that back into the hard-sphere equation, you end up with the Born-Land equation: As you might expect, the Born-Land equation gives a better prediction of the lattice energy than the hard-sphere model. The bond energy of Cl2 is 242.6kJ/mol of CI-Cl bonds. As calcium is a white crystalline solid and hence, the first step would be the conversion of solid calcium to gaseous calcium atom by providing sublimation energy (Hsub) because metals can donate their electrons only in gaseous form. The value for the lattice energy is the difference between the value from Step 1 and the value from Step 4. Calcium chloride in water decreases the freezing point of water and hence, it prevents the formation of ice and is used for de-icing. The starting point for such a model is the potential energy between two gaseous ions: Two alterations are necessary to make the above equation suitable for a mole of a lattice. The ionic solid CaCl would have the largest lattice energy. How do you find the lattice energy of CaCl2? Cl2(g)--> 2Cl(g) dH = 242.6 kJ It is hygroscopic in nature and hence, used in the desiccators for drying chemicals. This constant varies from lattice structure to lattice structure, and the most common are present in the lattice energy calculator. Ca (s) + Cl 2(g) CaCl 2(s) H f 0 = -795 KJ mol-1. 2003-2023 Chegg Inc. All rights reserved. The nearest neighbors of Na+ are 6 Cl- ions at a distance 1r, 12 Na+ ions at a distance 2r, 8 Cl- at 3r, 6 Na+ at 4r, 24 Na+ at 5r, and so on. For NaCl, the lattice dissociation enthalpy is +787 kJ mol-1. As metals have low ionization energy and hence, they can easily transfer their electron to another atom. Check out 4 similar electrochemistry calculators , What is lattice energy? For calcium, the first IE = 589.5 kJ mol-1, the second IE = 1146 kJ mol-1. Now, it is easy to remove an electron by providing a small amount of energy because it will achieve a stable noble has configuration i.e., the Argon atom. Evaluate the energy of crystallization, Ecryst . This will cause a release of energy, which is called the lattice energy. However, the crystalline structure allows each ion to interact with multiple oppositely charge ions, which causes a highly favorable change in the enthalpy of the system. This can be thought of in terms of the lattice energy of NaCl\text{NaCl}NaCl: That the ions are in their gaseous state is important; in this form, they are thought to be infinitely far apart, i.e., there are no interactions between them. The hydration enthalpy is the enthalpy change when 1 mole of gaseous ions dissolve in sufficient water to give an infinitely dilute solution. Calculate the lattice energy of Cacl2? Me molesta que mis padres no ______ (cuidar) su alimentacin.. 3. The values of the lattice energy for MgCl2, CaCl2, and SrCl2 are 2522 kJ/mol, 2253 kJ/mol, and 2127 kJ/mol, respectively. After this, the amount of energy you put in should be the lattice energy, right? 2nd Ionization Energy of Ca = 1145 $ kJ $ Bond Energy of Cl2 = 242.7 $ kJ $ Electron Affinity for chlorine = 2 $ \times $ (349 $ kJ $ ) Standard Enthalpy of Formation of CaCl2 (s) = 795 $ kJ $ We can substitute these values in the equation to find out the lattice energy The lattice energy is usually given in kilojules per mole (kJ/mol). This is a geometrical factor, depending on the arrangement of ions in the solid. Enter the the Ksp expression forC2D3 in terms of the molar solubility x.? "Thermodynamics of the Relationship between Lattice Energy and Lattice Enthalpy." \[\ce{M_{a} L_{b} (s) \rightarrow a M^{b+} (g) + b X^{a-} (g) } \label{eq1}\]. This energy is known as Lattice Energy (U) and its value depends upon the strength of the Ionic bond. An Hinglish word (Hindi/English). You can either construct a Born-Haber cycle or use a lattice energy equation to find lattice energy. Chichester: Horwood, 1994. Therefore, option (c) is correct. There are however difficulties in getting reliable energetic readings. Ca(OH)2 + 2HCl -> CaCl2 + 2H2O, Calcium chloride can also be produced from limestone by the Solvay process i.e. Combs, Leon. Experts are tested by Chegg as specialists in their subject area. The ionization energy of M is IE = 433 kJ/mol. \[ E_{cryst} = \dfrac{N Z^2e^2}{4\pi \epsilon_o r} \left( 1 - \dfrac{1}{n} \right)\label{6.13.3a} \]. Ladd, Mark. Moving all of the other constants into a single factor gives the final result: As you can see, the lattice energy can now be found from only the lattice's chemical formula and the ionic radii of its constituent atoms. (1) M a L b ( s) a M b + ( g) + b X a ( g) This quantity cannot be experimentally determined directly, but it can be estimated using a Hess Law approach in the form of Born-Haber cycle. For example, Cl exists as Cl2 in its elemental state. Calculate the lattice enegry of CaCl2 from the given data. Unfortunately, some of the factors for both the Born-Land and Born-Mayer equations require either careful computation or detailed structural knowledge of the crystal, which are not always easily available to us. Hence, ionic bond results when there is transferring of electron (s) either from one atom to another atom or from metal to nonmetal. Does MgCl2 have a high lattice energy? Lattice energy is defined as the energy released during the conversion of gaseous ions into their corresponding solid ions. DeltaHf (Na2O (s))=-414kJ/mol Delta H sublimation(Na)=109 kJ/mol I.E. This is permalink. Why is my internet redirecting to gslbeacon.ligit.com and how do I STOP THIS. The calcium chloride compound consists of one calcium atom and two chlorine atoms. A lot of energy is released as the oppositely charged ions interact. The chemical bond is the force of attraction between the atoms of the molecule, which brings atoms together in their chemical structure. Therefore. However, it is not true in the case of the calcium atom i.e., alkaline earth metals. Calculate the enthalpy of solution per mole of solid CaCl2. and hence, the calcium atom will lose its electron easily. Completa las oraciones con la forma correcta del presente de subjuntivo de los verbos entre parntesis.? of the corresponding inert gases are given below: The following values of n have been suggested for some common solids: Estimate the energy of crystallization for \(\ce{NaCl}\). Lattice energy is often used to estimate the strength of an ionic bond. Now the metal and nonmetal will be combined to form the ionic solid. The lattice energy of CaO is 3460 kJ/mol. As we know that the calcium atom belongs to group 2 of the modern periodic table and hence, it is a metal. It is an inorganic . 2 k J m o l -. As elements further down the period table have larger atomic radii due to an increasing number of filled electronic orbitals (if you need to dust your atomic models, head to our quantum numbers calculator), the factor r++rr^++r^-r++r increases, which lowers the overall lattice energy. Vol. Calculate the lattice energy of Cacl2 given that the heat of sublimation of Ca=121 kJ/mol and Hf Cacl2=-795 first ionization of ca = 589.5 second ionization of ca = 1145 the electron affinity of Cl = 349 the cl2 bond energy is 242.7 I have found all information that i believe are needed to When methods to evaluate the energy of crystallization or lattice energy lead to reliable values, these values can be used in the Born-Haber cycle to evaluate other chemical properties, for example the electron affinity, which is really difficult to determine directly by experiment. So, is CaCl2 Ionic or Covalent? You can ask a new question or browse more Chemistry questions. ---------------------------------- Hess' Law states that the overall energy of a reaction may be determined by breaking down the process into several steps, then adding together the changes in energy of each step. Lattice Energy is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by LibreTexts. Comparing the lattice energies of the three salts, students could now be asked to look at the relative strengths of the bonds in the compounds to relative sizes of ions and relative charge on ions. The Born-Haber cycle to evaluate Elattice is shown below: Ecryst = -411-(108+496+244/2)-(-349) kJ/mol Journal of Chemical Education. The other definition says that lattice energy is the reverse process, meaning it is the energy released when gaseous ions bind to form an ionic solid. Jimmy aaja, jimmy aaja. How is lattice energy estimated using Born-Haber cycle? The chlorine atom exists in diatomic form i.e., Cl2. (Elements in their natural state have an energy level of zero.) Lattice energy formulas, such as the Kapustinskii equation, are easy to use but are only estimates. You should talk about "lattice formation enthalpy" if you want to talk about the amount of energy released when a lattice is formed from its scattered gaseous ions. LiCl, NaCl, CaCl2, Al2O3. How Ionic Bond formation takes place in Calcium Chloride, Differentiation between Ionic and Covalent bond. The Born-Haber Cycle requires that the elements involved in the reaction are in their gaseous forms. It has ions with the largest charge. Perhaps surprisingly, there are several ways of finding the lattice energy of a compound. Therefore, the hard-sphere equation for lattice energy is: While the hard-sphere model is a useful approximation, it does have some issues. Generally, calcium chloride is found in the hydrated form i.e., CaCl2 (H2O)n, where n = 0, 1, 2, 4, and 6. The formation of calcium chloride can be explained by the Born Haber cycle. The lattice energy is the total potential energy of the crystal. In other words, treating the AgCl as 100% ionic underestimates its lattice enthalpy by quite a lot. Next, the electron affinity of the nonmetal will be subtracted from the previous value. Hf of NaCl = -411 (Enthalpy of formation). You can find the polarity of a compound by finding electronegativities (an atoms desire for an electron) of the atoms; Carbon has an electronegativity of 2.5, compared to Fluorines A) Enter the the Ksp expression for the solid AB2 in terms of the molar solubility x. They are instead surrounded by a number of electron orbitals regardless of charge (unless you have managed to remove all of the electrons, as in the case of H+\text{H}^+H+, of course). CaCO3 + 2NaCl CaCl2 + Na2CO3, Calcium chloride produces free calcium ions i.e., the aqua complex of calcium ion and chloride ion by dissolving themselves in water as follows, CaCl2 + 6H2O > [Ca(H2O)6]2+ + 2Cl. The Madelung constant depends on the structure type, and its values for several structural types are given in Table 6.13.1. 4 Answers aaja Come. We will discuss one briefly, and we will explain the remaining four, which are all slight variations on each other, in more detail. to the empployees was very informative. The above discussion is valid only for the sodium chloride (also called rock salt) structure type. Which one of the following has the largest lattice energy? Explain your trouble. kJ/mol CaCl2 Submit Submit Answer Try Another Version 9 item attempts remaining This problem has been solved! The compound does not dissolve in water. However, this sharing may be equal or unequal depending on the electronegativity of the constituent atoms of the molecules. As implied in the definition, this process will always be exothermic, and thus the value for lattice energy will be negative. Therefore, the hard-sphere equation for lattice energy is: U=\frac {N_ {\text {A}}z^+z^-e^2 M} {4\pi\varepsilon_0r_0} U = 40r0N Az +z e2M where: N_ {\text {A}} N A Avogadro's number; and M M Madelung constant. Rearrangement to solve for lattice energy gives the equation: Lattice energy= Heat of formation- Heat of atomization- Dissociation energy- (sum of Ionization energies)- (sum of Electron Affinities). Step-by-step solution Step 1 of 5 The standard enthalpy of formation of an ionic solid from its constituent elements is given by Hess's Law: .. (1) In the equation, = the standard enthalpy of formation of the solid compound The electron affinity of Cl is -348 kJ mol-1. Still, if you would like us to add some more, please feel free to write to us . Diaphragm _____ 3. where can i find red bird vienna sausage? Both the metal and nonmetal now need to be changed into their ionic forms, as they would exist in the ionic solid. Mi hermana se sorprende N-F C-F Cl-F F-F 2 Answers C-F is the most polar. The Born-Haber cycle allows us to understand and determine the lattice energies of ionic solids. Charge on the ion 2. MgCl2 Expert Answer 100% (6 ratings) Let us First consider the Born-Lande equation for computing Lattice Energy- So from the equation,two things are clear which the Lattice Energy U depends on- The Charge on the ions- Lattice Energy U is directlry proportional with the charge View the full answer Previous question Next question Therefore, the first step would be the dissociation of chlorine elements into chlorine atoms and the next step would be acceptance of electrons. If you get a different value, please let me know. How would the energy of the ionic bond be affected by the following changes? The first major improvement came from Mayer, who found that replacing 1/rn1/r^n1/rn with ere^{-\frac{r}{\rho}}er yielded a more accurate repulsion term. Ca(s) + Cl2(g) ==> CaCl2(s) dHformation = -795 kJ. Corrundum Al2O3 has some covalent character in the solid as well as the higher charge of the ions. This kind of construction is known as a Born-Haber cycle. Using formulae, the lattice energy at any conditions can be found as the . Thus, the energy due to one ion is, \[ E = \dfrac{Z^2e^2}{4\pi\epsilon_or} M \label{6.13.1}\]. I am Savitri,a science enthusiast with a passion to answer all the questions of the universe. Calculate the lattice energy of Cacl2 given that the heat of sublimation of Ca=121 kJ/mol and Hf Cacl2=-795. As an example, let us consider the the NaCl crystal. "Lattice Energy". L ;-{f}`Js4/c)Y:& "4+MKT08c3&_`%5&C^2h |': ^\. Lattice Energy: The Born-Haber cycle is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by LibreTexts. Ea for F = -328 E11 forCs = +375.7 E12 for Cs = +2422 Heat of sublimation for Cs =, Na+(g) + Br-(g) --> NaBr (s) Hint: use the Born-Haber cycle Note: the reference state for Br2 is Br2(l) not Br2(g) Data (in kJ/mol): enthalpy of sublimation of Na(s): 107 standard enthalpy, I have to place the following in order of decreasing magnitude of lattice energy, but I don't know how to do it. This definition causes the value for the lattice energy to always be positive, since this will always be an endothermic reaction. It is, however, still an approximation, and improvements to the repulsion term have since been made. For NaCl, the lattice formation enthalpy is -787 kJ mol-1. So, how to calculate lattice energy experimentally, then? Lattice Energy= [-436.68-89-(0.5*158)-418.8-(-328)] kJ/mol=, Lattice Energy= [-641.8-146-243-(737.7+1450.6)-(2*-349)] kJ/mol=. For a single atom in the lattice, the summation of all of these interactions can be found, known as the Madelung constant, MMM, which is then multiplied by the equation above. It is a two-step process i.e., loss of one electron per step. (O -) = 878 kJ/mol Use this information to calculate the lattice energy of Na2O (s). Ca2+(g) +2e- +2Cl(g) (up arrow) enthalpy ionisation down arrow electron affinity Ca+(g) + e- +2Cl(g) Ca2+(g) +2Cl-(g) (up arrow) enthalpy ionisation down arrow lattice enthalpy Ca(g) +2Cl(g) (up arrow) enthalpy atomisation Ca(g) +Cl2(g) (up arrow) enthalpy atomisation Ca (s) +Cl2(g) down arrow) enthalpy formation CaCl2(S) Lattice enthalpy = enthalpy formation enthalpy atomisation for calcium 2x enthalpy atomisation for chlorine-1st and second ionisation energies for calcium electron affinity for Clx2, Your email address will not be published. 2*Cl(g) + 2e -->2*Cl^-(g) dH =2*-348 kJ Lattice energy i s the heat of formation when one mole of crystalline ionic solid is generated from its constituent ions in their gaseous state. Calcium chloride is crystalline in nature and can be easily dissolved in water. This is because ions are generally unstable, and so when they inevitably collide as they diffuse (which will happen quite a lot considering there are over 600 sextillion atoms in just one mole of substance as you can discover with our Avogadro's number calculator) they are going to react to form more stable products. Circle skirt calculator makes sewing circle skirts a breeze. Ca2+ (g) + 2Cl-(g) CaCl2 (s) + U. In one definition, the lattice energy is the energy required to break apart an ionic solid and convert its component atoms into gaseous ions. Work Plz. There are many other factors to be considered such as covalent character and electron-electron interactions in ionic solids. The Born-Haber Cycle can be reduced to a single equation: Heat of formation= Heat of atomization+ Dissociation energy+ (sum of Ionization energies)+ (sum of Electron affinities)+ Lattice energy. The Lattice energy, \(U\), is the amount of energy required to separate a mole of the solid (s) into a gas (g) of its ions. When an atom forms a chemical bond, it tends to achieve the nearest noble gas configuration. Which one of the following has the greatest lattice energy? No creo que Susana _____ (seguir) sobre los consejos de su mdico. It is this that causes ionic solids to have such high melting and boiling points. For these reasons they have not been included in the present lattice energy calculator. Suzuki, Takashi. However, many nonmetals will exist as polyatomic species. Hence, the second ionization energy of calcium is smaller than the first ionization energy. A chemical bond is formed either by transferring electrons or by sharing electrons between atoms of the molecule. Ca^+(g) --> Ca^2+ + e dH = + 1146 kJ MgO. the energy released is called energy of crystallization (\(E_{cryst}\)). 2. In one definition, the lattice energy is the energy required to break apart an ionic solid and convert its component atoms into gaseous ions. Discussion _____ 1. This is the energy of the ionic solid, and will be used at the end of the process to determine the lattice energy. Substituting this new approximation into the Born-Land equation gives: Since then, further improvements in our understanding of the universe have lead to a more accurate repulsion term, which in turn have given better equations for how to calculate lattice energy. The positive ions experience both attraction and repulson from ions of opposite charge and ions of the same charge. Table 8.2 Figure 7.9 Some are given here. But for simplicity, let us consider the ionic solids as a collection of positive and negative ions. The ionic bond is the chemical bond between metal and nonmetal. - The lattice energy definition, How to calculate lattice energy - The lattice energy formula. The enthalpies of formation of the ionic molecules cannot alone account for this stability. The lattice energies for NaCl most often quoted in other texts is about 765 kJ/mol. Express your answer in terms of x. (a) Based on the lattice energies of MgCl2 and SrCl2 given in Table 8.2, what is the range of values that you would expect for the lattice energy of CaCl2? In this simple view, appropriate number of cations and anions come together to form a solid. It is subtracted because it is a release of energy associated with the addition of an electron. Size of the ion On comparing the four given compounds we can see that, M gO and CaO have higher charges (+2 and -2 on the cations and anions respectively) than N aCl and KCl (+1 and -1 on the cations and anions respectively). Metals exist in nature as single atoms and thus no dissociation energy needs to be added for this element. Ca(s) --> Ca(g) dH = +192 kJ Using the values giving in the discussion above, the estimation is given by Equation \ref{6.13.3a}: \[ \begin{align*} E_cryst&= \dfrac{(6.022 \times 10^{23} /mol (1.6022 \times 10 ^{-19})^2 (1.747558)}{ 4\pi \, (8.854 \times 10^{-12} C^2/m ) (282 \times 10^{-12}\; m} \left( 1 - \dfrac{1}{9.1} \right) \\[4pt] &= - 766 kJ/mol \end{align*}\]. The crystal lattice energy has influence on other physical and chemical properties: melting temperature (the higher lattice energy, the higher melting temperature), The science, which deals with crystals properties is, There are theroretical models, which allow to calculate (with better or worse result) the lattice energy. I have found all information that i believe are needed to solve this question .. yet i dont know how to solve the question! Your email address will not be published. PLEASE HELP!!! Some might expect such an ordered structure to be less stable because the entropy of the system would be low. Ladd, Mark. However, lattice energy cannot be directly measured. Sometimes on Family Guy when there about to take someones heart out they say, calimar or maybe its spelled different. Crystal Structures: Lattices and Solids in Stereoview. Madelung constants for a few more types of crystal structures are available from the Handbook Menu. Spanish Help If energy is released, put a negative sign in front of the value; if energy is absorbed, the value should be positive. (a) doubling . Accessibility StatementFor more information contact us atinfo@libretexts.orgor check out our status page at https://status.libretexts.org. The lattice energy is the total potential energy of the crystal. The molecular weight of its anhydrous form is 111 g/mol. Electron affinity : Cl (g) + e- Cl-(g) H 3 = -355 KJ mol-1 where N is the Avogadro's number (6.022x10-23), and n is a number related to the electronic configurations of the ions involved. In fact, there are five. Posterior Thigh _____ 4. 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However, the melting point of hexahydrate calcium chloride is only 29.9 C. Before we get to grips with finding the lattice energy, it's important to know the lattice energy definition as it is quite peculiar. *Note: In this general equation, the electron affinity is added. Calculate the lattice energy of CaCl2 from the given data, \[\ce{Ca_{(s)} + Cl2_{(g)} -> CaCl2_{(s)}}\] `"H"_"f"^0` = 795 kJ mol1, Sublimation: \[\ce{Ca_{(s)} -> Ca-{(g)}}\] `"H"_1^0` = + 121 kJ mol1, Ionisation: \[\ce{Ca_{(g)} -> Ca^2+_{(g)} + 2e^-}\] `"H"_2^0` = + 2422 kJ mol1, Dissociation: \[\ce{Cl2_{(g)} -> 2Cl_{(g)}}\] `"H"_3^0` = + 242.8 kJ mol1, Electron affinity: \[\ce{Cl_{(g)} + e^- -> Cl^-_{(g)}}\] `"H"_4^0` = 355 kJ mol1, 795 = 121 + 2422 + 242.8 + (2 355) + u, Chapter 7: Thermodynamics - Evaluation [Page 226], Tamil Nadu Board Samacheer Kalvi Class 11th Chemistry Volume 1 and 2 Answers Guide, Maharashtra Board Question Bank with Solutions (Official), Mumbai University Engineering Study Material, CBSE Previous Year Question Paper With Solution for Class 12 Arts, CBSE Previous Year Question Paper With Solution for Class 12 Commerce, CBSE Previous Year Question Paper With Solution for Class 12 Science, CBSE Previous Year Question Paper With Solution for Class 10, Maharashtra State Board Previous Year Question Paper With Solution for Class 12 Arts, Maharashtra State Board Previous Year Question Paper With Solution for Class 12 Commerce, Maharashtra State Board Previous Year Question Paper With Solution for Class 12 Science, Maharashtra State Board Previous Year Question Paper With Solution for Class 10, CISCE ICSE / ISC Board Previous Year Question Paper With Solution for Class 12 Arts, CISCE ICSE / ISC Board Previous Year Question Paper With Solution for Class 12 Commerce, CISCE ICSE / ISC Board Previous Year Question Paper With Solution for Class 12 Science, CISCE ICSE / ISC Board Previous Year Question Paper With Solution for Class 10, HSC Science Class 11th Tamil Nadu Board of Secondary Education. Discussion:This number has not been checked. Chichester: Horwood, 1999. In calcium chloride, the calcium atom donates its two electrons and become cation whereas each chlorine atom gain one electron, donated by Calcium, and get a negative charge. The Kb of pyridine, C5H5N, is 1.5 x 10-9. Some require such high temperatures that they decompose before they can reach a melting and/or boiling point. You'll get a detailed solution from a subject matter expert that helps you learn core concepts. Save my name, email, and website in this browser for the next time I comment. Hess' Law allows us to add or subtract these values, which allows us to determine the lattice energy. What is the lattice energy? IP of Na(g) = 496 (Ionization potential or energy) A highly concentrated solution of calcium chloride on the road prevents the formation of the dust owing to its hygroscopic nature and forming a liquid layer on the surface of the road. The other trend that can be observed is that, as you move down a group in the periodic table, the lattice energy decreases. CaCl2 is an ionic compound owing to the large electronegativity difference between the calcium atom and chlorine atom, which is greater than 2.0. Save my name, email, and website in this browser for the next time I comment. You're probably well aware of how ubiquitous ionic lattices are - you'll find them in your food, medicine, and maybe even in the walls of your house - but by learning what lattice energy is, the lattice energy formula, and the lattice energy trend, your appreciation for chemistry will surely increase. Calculate the lattice enthalpy of CaCl 2, given that :Enthalpy of sublimation for Ca s Ca g =121 kJ mol 1Enthalpy of dissociation of Cl 2 g 2 Cl g =242.8 kJ mol 1Ionisation energy of Ca g Ca ++ g =2422 kJ mol 1Electron gain enthalpy of 2 Cl 2 Cl 1 =2 355 kJ mol 1= 710 kJ mol 1Enthalpy of formation of CaCl 2= 795 kJ mol 1A.