Explore a chemical reaction at the molecular level. Given that heat of combustion of benzene at constant volume is at , heat of combustion (in kJ ) of benzene at constant pressure will be
(R = 8.314 JK–1 mol–1) 3:27 100+ LIKES. Also, learn how compounds arrange themselves. The emphasis initially is on the U value, because the reaction is carried out experimentally in a closed, constant-volume apparatus and the experimentally measured quantity is the heat associated with the process. Since U = q V, a measurement of q V gives U directly. The following formula is used to calculate the heat of combustion. The heats of formation of carbon dioxide and water vapor are 393.509 kJ/mol and 241.818 kJ/mol, respectively, at 25 oC and one bar pressure. Heat of Combustion Formula. Standard enthalpies of formation of CO2 (g) and H2O (1) are -393.5 kJ mol-1 and -285.83 kJ mol-1, respectively. Benzene has a heat of vaporization of 30.72 kj/mol and a normal boiling point of 80.1 degrees celcius. The heats of combustion of benzene, toluene, ethylbenzene, o-xylene, m-xylene, p-xylene, n-propylbenzene, and styrene were measured with a bomb calorimeter. Standard enthalpy of combustion () is the enthalpy change when 1 mole of a substance burns (combines vigorously with oxygen) under standard state conditions; it is sometimes called heat of combustion. In this lesson, we will discuss the bond enthalpy in chemical reactions. The results of these reactions can be used to identify the metal in the ionic compound. Rate of a Chemical Reaction: Modifying Factors. Given the following reactions 2 NO(g) N2(g) + ... Standard Enthalpy of Formation: Explanation & Calculations. Verify the result by using the general equation for finding enthalpies of reaction from enthalpies … The definition of a calorimeter, uses for calorimeters, and the calorimetry equation will be discussed. What is the standard heat of formation of benzene? The heat of combustion of benzene, C6H6, is -41.74 kJ/g. Determining Rate Equation, Rate Law Constant & Reaction Order from Experimental Data. The standard heat of combustion of liquid benzene (giving water vapor) is 40.145kJ/g at 25 oC. Is it possible to change how fast a reaction occurs? That is the magic of entropy. Benzene (c6h6) is -3727. For example, the enthalpy of combustion of ethanol, 1366.8 kJ/mol, is the amount of heat produced when one mole of ethanol undergoes complete combustion at 25 °C and 1 atmosphere pressure, yielding products also at 25 °C and 1 atm. In this lesson, you will learn how gases behave when they are mixed together and how to use Dalton's law of partial pressures to calculate partial and total pressures of gases. The combustion of one mole of benzene takes place at 298 K and 1 atm. This lesson defines state functions and explains why state functions are so useful in thermochemistry and thermodynamics. View desktop site. HC = LHV + H v * ( NH20 / NFuel). - Definition, Uses & Equation. All other trademarks and copyrights are the property of their respective owners. 6C + 2H2 gives C6H6 The standard enthalpy of combustion of Benzene is -3266.0 kJ and standard enthalpy of formation of CO2 and H2O are -393.1 kJ and -286.0 kJ … After combustion, CO2 (g)and H2O (l) are produced and 3267.0 kJ of heat is liberated. By knowing how to draw and label an enthalpy diagram we can see what the starting energy level is, how much energy is needed to get the reaction going, and what energy is left at the end of a chemical reaction. © copyright 2003-2021 Study.com. What the figure of +49 shows is the relative positions of benzene and its elements on an energy diagram: The heats of formation of carbon dioxide and water vapor are 393.509 kJ/mol and 241.818 kJ/mol, respectively, at 25 oC and one bar pressure. NIST / TRC Web Thermo Tables, professional edition (thermophysical and thermochemical data) Standard heat of combustion is kJ per 1 mole of benzene. combustion, Um,comb, as Um,comb = –3,228.29 ± 0.24 kJ/mol. Here, \Delta H indicates the change in enthalpy of the chemical reaction, {eq}\Delta {{H}_{p}} {/eq} indicate the change in enthalpy of the product and {eq}\Delta {{H}_{r}} {/eq} indicates the change in enthalpy of the reactant. Earn Transferable Credit & Get your Degree, Get access to this video and our entire Q&A library. Comparing Compounds Based on Boiling Point. You'll also see a few examples of common state functions. The heating value (or energy value or calorific value) of a substance, usually a fuel or food (see food energy), is the amount of heat released during the combustion of a specified amount of it.. Calculate the standard enthalpy of formation, Δf H° of benzene. Homework Statement: Calculate the heat Kcal measured at 25.0°C and 1 atm corresponding to the complete combustion of 4.00 L of Benzene … The heat of combustion of benzene in a bomb calorimeter (i.e., constant volume) was found to be 3263.9 kJ mol^–1 at 25°C. 2.4k VIEWS. Go to tabulated values. We will also learn how we can use these values as one way to calculate the standard enthalpy change of a chemical reaction. For example, the standard enthalpy change of formation for liquid benzene is +49 kJ mol-1. Hess's Law: Definition, Formula & Examples. Solve each by combining the known thermochemical equations using the Heat of Formation values below. Benzene, C6H6, is a clear colorless to light-yellow liquid, flammable with a petroleum-like, aromatic odor. The standard heat of combustion of benzene is -3271 kJ/mol. The heats of formation of CO2(g) and H2O(l) are -394 kJ/mole and -285.8 kJ/mole respectively. Std. The experimental data shown in these pages are freely available and have been published already in the DDB Explorer Edition.The data represent a small sub list of all available data in the Dortmund Data Bank.For more data or any further information please search the DDB or contact DDBST.. In this lesson, we'll define chemical entropy as a thermodynamic function, discuss positional entropy as it relates to the states of matter, and state the second law of thermodynamics. For example, the heat of formation of water vapor is defined by the reaction: H 2 (g) + 1/2 O 2 (g) H 2 O (g) Sodium hydroxide is a base, and it reacts with metallic ions. 2C6H 6(l) +15O2(g) → 12CO2(g) + 6H 2O(l), ΔH rxn = -6546 kJ Bond Enthalpy: Definition, Calculations & Values. Answer to: The standard heat of combustion of benzene, C6H6, is –3301 kJ/mol at 1 atm and 25°C. The balanced chemical equation for the combustion of benzene, C6H 6, is 2C6H 6(l) +15O2(g) → 12CO2(g) + 6H 2O(l) Now, in order to have the thermochemical equation, you need to add the change in enthalpy associated with this reaction, which is listed as being equal to -6546 kJ. Should it just be 6C(s) + 3H2(g) -----> C6H6. Of combustion (in kJ mol). chemistry. what is the molar heat of combustion of benzene, C6H6, if combustion of 1.00 g of benzene causes a temperature rise of 5.18 C in a bomb calorimeter that has a heat capacity of 8.07 kJ/C? We'll review intermolecular forces and how they influence the boiling point of molecules with different structures. In this lesson, we learn about Hess's Law and how to use enthalpy of formation and enthalpy of combustion to calculate the change in enthalpy using Hess's law. Why are some reactions much faster than others? The standard heat of combustion of liquid benzene (giving water vapor) is 40.145kJ/g at 25 oC. Component Our experts can answer your tough homework and study questions. What is a Calorimeter? In this lesson, we'll review what intermolecular forces are and how they will affect physical properties such as boiling point, freezing point, melting point, and vapor pressure. Lewis Structures: Single, Double & Triple Bonds. Calculate the enthalpy change for the formation of benzene (C6H6) from the elements at 25 oC and one bar pressure. Heat of formation is defined as the enthalpy change when one mole of a compound is formed from the elements in their stable states. Calculate the standard enthqlpy of the formation of benzene give the following standard enthalpies? Energy is required to break bonds when a chemical reaction occurs, and this is called the bond enthalpy. The standard heat of combustion of benzene is ΔH =−3271 kJ/mol Δ H = − 3271 kJ/mol The heat of formation of carbon dioxide (CO2) is... See full answer below. The following values were obtained for the heat of combustion, at 25° C and constant pressure, of the liquid hydrocarbon in … Dalton's Law of Partial Pressures: Calculating Partial & Total Pressures. Where HC is the heat of combustion ; LHV is the lower heating value C6H6 (l) + 15/2 O2 (g) à 6 CO2 (g) + 3 H2O (l) Answer: -3,236.9 J UST - DEPARTMENT OF CHEMICAL ENGINEERING 8 3/9/20 "Calculate the standard enthalpies of reaction for combustion reactions in which ethane (C2H6), and benzene (C6H6) are the respective reactants and CO2(g) and H20(l) are the products in each. Benzene is less dense than water and is slightly soluble in water.Hence it floats on water.Benzene vapor is heavier than air. Calculate the enthalpy of reaction. Science 102: Principles of Physical Science, General Chemistry Syllabus Resource & Lesson Plans, Organic & Inorganic Compounds Study Guide, SAT Subject Test Chemistry: Practice and Study Guide, DSST Principles of Physical Science: Study Guide & Test Prep, Principles of Physical Science: Certificate Program, College Chemistry: Homework Help Resource, To learn more about the information we collect, how we use it and your choices visit our, Biological and Biomedical An enthalpy diagram allows us to easily see details of a chemical reaction. This lesson will discuss how the boiling point of a compound changes based on its molecular structure. The equation is: If carbon won't react with hydrogen to make benzene, what is the point of this, and how does anybody know what the enthalpy change is? The standard heat of combustion of benzene is -3271 kJ/mol. Calculate the heat of combustion of one mole of C6H6. When benzene, below Figure, is combusted it has the following stoichiometric reaction C6 H6 + 15/2 O2 → 6CO2 + 3 H2O The enthalpy change for this combustion reaction is equal to the sum of the standard enthalpies of formation ΔH 0 of the products minus the sum of the standard enthalpies of formation of the reactants. You will also learn how to use this information to explain how to find the partial pressure of a gas collected over water. Calculate the standard enthalpy of combustion for the following reaction: C2H5OH(ℓ) + 7⁄2O2(g) ---> … & Learn what the common ion effect is, how to make equilibrium calculations involving it, and how to find the concentrations of ions when adding reactions in equilibrium to solutions that already contain ions. Terms In this lesson, you'll learn how varying the conditions of concentration, temperature, and pressure will affect the reactants and products in a chemical reaction at equilibrium. Learn how to represent single, double and triple bonds with lines instead of dots. Combustion of 3.65 of benzene causes a temperature rise of 4.41 C^o in a certain bomb calorimeter. How to Identify Chemicals in Solution: Test Methods & Materials. (b) Compare the quantity of heat… C = -393.5 h2 is 285.5. Using Sodium Hydroxide Solution to Identify Metal Ions. Standard heat of combustion: The energy liberated when a … Sciences, Culinary Arts and Personal Two scientists came to a conclusion: an acidic solution behaves as proton donors, which is in the form of a hydrogen ion. Review what a Lewis dot diagram is and discover how to draw a Lewis dot structural formula for compounds. Do you have a mysterious solution sitting around? A standard enthalpy of formation is an enthalpy change for a reaction in which … Calculate the enthalpy change for the formation benzene from the elements at 25 oC and one bar. This is what we call the Bronsted-Lowry definition of an acid, which is the main focus of this lesson. In this lesson, we will learn how to conduct these tests and interpret the results. Benzene causes central nervous system damage acutely and bone marrow damage chronically and is carcinogenic. Services, Using Hess's Law to Calculate the Change in Enthalpy of a Reaction, Working Scholars® Bringing Tuition-Free College to the Community, The standard heat of combustion of benzene is {eq}\Delta H=-3271\ \text{kJ/mol} {/eq}. This is one way to calculate the heat transferred, or enthalpy change, of a chemical reaction. Don't worry, this lesson will help you become a pro at all of these things by walking through two comprehensive problems that address all of these topics. Become a Study.com member to unlock this The standard enthalpy of formation of benzene, C6H6, is +49.2 kJ/mole. | Calculate its standard heat of formation, ? ?%, using the data: Hint: You need to write balanced equation for combustion of benzene. The standard heat of combustion of benzene is -3271 kJ/mol. Want to make sure you don't blow yourself up during a chemical reaction? The standard enthalpy of combustion of C2H6O(l) is -1,367 kJ mol-1 at 298 K. What is the standard enthalpy of formation of C2H6O(l) at 298 K? You will also discover how factors such as temperature, concentration, surface area, and catalysts impact reaction rates. In this lesson, you'll learn why disorder is the natural state of matter and how we can predict entropy change in a physical or chemical reaction. Predicting the Entropy of Physical and Chemical Changes. The mathematical expression of the change in enthalpy of a chemical reaction is shown below, {eq}\Delta H=\Delta {{H}_{p}}-\Delta {{H}_{r}} {/eq}.
(R = 8.314 JK–1 mol–1) 3:27 100+ LIKES. Also, learn how compounds arrange themselves. The emphasis initially is on the U value, because the reaction is carried out experimentally in a closed, constant-volume apparatus and the experimentally measured quantity is the heat associated with the process. Since U = q V, a measurement of q V gives U directly. The following formula is used to calculate the heat of combustion. The heats of formation of carbon dioxide and water vapor are 393.509 kJ/mol and 241.818 kJ/mol, respectively, at 25 oC and one bar pressure. Heat of Combustion Formula. Standard enthalpies of formation of CO2 (g) and H2O (1) are -393.5 kJ mol-1 and -285.83 kJ mol-1, respectively. Benzene has a heat of vaporization of 30.72 kj/mol and a normal boiling point of 80.1 degrees celcius. The heats of combustion of benzene, toluene, ethylbenzene, o-xylene, m-xylene, p-xylene, n-propylbenzene, and styrene were measured with a bomb calorimeter. Standard enthalpy of combustion () is the enthalpy change when 1 mole of a substance burns (combines vigorously with oxygen) under standard state conditions; it is sometimes called heat of combustion. In this lesson, we will discuss the bond enthalpy in chemical reactions. The results of these reactions can be used to identify the metal in the ionic compound. Rate of a Chemical Reaction: Modifying Factors. Given the following reactions 2 NO(g) N2(g) + ... Standard Enthalpy of Formation: Explanation & Calculations. Verify the result by using the general equation for finding enthalpies of reaction from enthalpies … The definition of a calorimeter, uses for calorimeters, and the calorimetry equation will be discussed. What is the standard heat of formation of benzene? The heat of combustion of benzene, C6H6, is -41.74 kJ/g. Determining Rate Equation, Rate Law Constant & Reaction Order from Experimental Data. The standard heat of combustion of liquid benzene (giving water vapor) is 40.145kJ/g at 25 oC. Is it possible to change how fast a reaction occurs? That is the magic of entropy. Benzene (c6h6) is -3727. For example, the enthalpy of combustion of ethanol, 1366.8 kJ/mol, is the amount of heat produced when one mole of ethanol undergoes complete combustion at 25 °C and 1 atmosphere pressure, yielding products also at 25 °C and 1 atm. In this lesson, you will learn how gases behave when they are mixed together and how to use Dalton's law of partial pressures to calculate partial and total pressures of gases. The combustion of one mole of benzene takes place at 298 K and 1 atm. This lesson defines state functions and explains why state functions are so useful in thermochemistry and thermodynamics. View desktop site. HC = LHV + H v * ( NH20 / NFuel). - Definition, Uses & Equation. All other trademarks and copyrights are the property of their respective owners. 6C + 2H2 gives C6H6 The standard enthalpy of combustion of Benzene is -3266.0 kJ and standard enthalpy of formation of CO2 and H2O are -393.1 kJ and -286.0 kJ … After combustion, CO2 (g)and H2O (l) are produced and 3267.0 kJ of heat is liberated. By knowing how to draw and label an enthalpy diagram we can see what the starting energy level is, how much energy is needed to get the reaction going, and what energy is left at the end of a chemical reaction. © copyright 2003-2021 Study.com. What the figure of +49 shows is the relative positions of benzene and its elements on an energy diagram: The heats of formation of carbon dioxide and water vapor are 393.509 kJ/mol and 241.818 kJ/mol, respectively, at 25 oC and one bar pressure. NIST / TRC Web Thermo Tables, professional edition (thermophysical and thermochemical data) Standard heat of combustion is kJ per 1 mole of benzene. combustion, Um,comb, as Um,comb = –3,228.29 ± 0.24 kJ/mol. Here, \Delta H indicates the change in enthalpy of the chemical reaction, {eq}\Delta {{H}_{p}} {/eq} indicate the change in enthalpy of the product and {eq}\Delta {{H}_{r}} {/eq} indicates the change in enthalpy of the reactant. Earn Transferable Credit & Get your Degree, Get access to this video and our entire Q&A library. Comparing Compounds Based on Boiling Point. You'll also see a few examples of common state functions. The heating value (or energy value or calorific value) of a substance, usually a fuel or food (see food energy), is the amount of heat released during the combustion of a specified amount of it.. Calculate the standard enthalpy of formation, Δf H° of benzene. Homework Statement: Calculate the heat Kcal measured at 25.0°C and 1 atm corresponding to the complete combustion of 4.00 L of Benzene … The heat of combustion of benzene in a bomb calorimeter (i.e., constant volume) was found to be 3263.9 kJ mol^–1 at 25°C. 2.4k VIEWS. Go to tabulated values. We will also learn how we can use these values as one way to calculate the standard enthalpy change of a chemical reaction. For example, the standard enthalpy change of formation for liquid benzene is +49 kJ mol-1. Hess's Law: Definition, Formula & Examples. Solve each by combining the known thermochemical equations using the Heat of Formation values below. Benzene, C6H6, is a clear colorless to light-yellow liquid, flammable with a petroleum-like, aromatic odor. The standard heat of combustion of benzene is -3271 kJ/mol. The heats of formation of CO2(g) and H2O(l) are -394 kJ/mole and -285.8 kJ/mole respectively. Std. The experimental data shown in these pages are freely available and have been published already in the DDB Explorer Edition.The data represent a small sub list of all available data in the Dortmund Data Bank.For more data or any further information please search the DDB or contact DDBST.. In this lesson, we'll define chemical entropy as a thermodynamic function, discuss positional entropy as it relates to the states of matter, and state the second law of thermodynamics. For example, the heat of formation of water vapor is defined by the reaction: H 2 (g) + 1/2 O 2 (g) H 2 O (g) Sodium hydroxide is a base, and it reacts with metallic ions. 2C6H 6(l) +15O2(g) → 12CO2(g) + 6H 2O(l), ΔH rxn = -6546 kJ Bond Enthalpy: Definition, Calculations & Values. Answer to: The standard heat of combustion of benzene, C6H6, is –3301 kJ/mol at 1 atm and 25°C. The balanced chemical equation for the combustion of benzene, C6H 6, is 2C6H 6(l) +15O2(g) → 12CO2(g) + 6H 2O(l) Now, in order to have the thermochemical equation, you need to add the change in enthalpy associated with this reaction, which is listed as being equal to -6546 kJ. Should it just be 6C(s) + 3H2(g) -----> C6H6. Of combustion (in kJ mol). chemistry. what is the molar heat of combustion of benzene, C6H6, if combustion of 1.00 g of benzene causes a temperature rise of 5.18 C in a bomb calorimeter that has a heat capacity of 8.07 kJ/C? We'll review intermolecular forces and how they influence the boiling point of molecules with different structures. In this lesson, we learn about Hess's Law and how to use enthalpy of formation and enthalpy of combustion to calculate the change in enthalpy using Hess's law. Why are some reactions much faster than others? The standard heat of combustion of liquid benzene (giving water vapor) is 40.145kJ/g at 25 oC. Component Our experts can answer your tough homework and study questions. What is a Calorimeter? In this lesson, we'll review what intermolecular forces are and how they will affect physical properties such as boiling point, freezing point, melting point, and vapor pressure. Lewis Structures: Single, Double & Triple Bonds. Calculate the enthalpy change for the formation of benzene (C6H6) from the elements at 25 oC and one bar pressure. Heat of formation is defined as the enthalpy change when one mole of a compound is formed from the elements in their stable states. Calculate the standard enthqlpy of the formation of benzene give the following standard enthalpies? Energy is required to break bonds when a chemical reaction occurs, and this is called the bond enthalpy. The standard heat of combustion of benzene is ΔH =−3271 kJ/mol Δ H = − 3271 kJ/mol The heat of formation of carbon dioxide (CO2) is... See full answer below. The following values were obtained for the heat of combustion, at 25° C and constant pressure, of the liquid hydrocarbon in … Dalton's Law of Partial Pressures: Calculating Partial & Total Pressures. Where HC is the heat of combustion ; LHV is the lower heating value C6H6 (l) + 15/2 O2 (g) à 6 CO2 (g) + 3 H2O (l) Answer: -3,236.9 J UST - DEPARTMENT OF CHEMICAL ENGINEERING 8 3/9/20 "Calculate the standard enthalpies of reaction for combustion reactions in which ethane (C2H6), and benzene (C6H6) are the respective reactants and CO2(g) and H20(l) are the products in each. Benzene is less dense than water and is slightly soluble in water.Hence it floats on water.Benzene vapor is heavier than air. Calculate the enthalpy of reaction. Science 102: Principles of Physical Science, General Chemistry Syllabus Resource & Lesson Plans, Organic & Inorganic Compounds Study Guide, SAT Subject Test Chemistry: Practice and Study Guide, DSST Principles of Physical Science: Study Guide & Test Prep, Principles of Physical Science: Certificate Program, College Chemistry: Homework Help Resource, To learn more about the information we collect, how we use it and your choices visit our, Biological and Biomedical An enthalpy diagram allows us to easily see details of a chemical reaction. This lesson will discuss how the boiling point of a compound changes based on its molecular structure. The equation is: If carbon won't react with hydrogen to make benzene, what is the point of this, and how does anybody know what the enthalpy change is? The standard heat of combustion of benzene is -3271 kJ/mol. Calculate the heat of combustion of one mole of C6H6. When benzene, below Figure, is combusted it has the following stoichiometric reaction C6 H6 + 15/2 O2 → 6CO2 + 3 H2O The enthalpy change for this combustion reaction is equal to the sum of the standard enthalpies of formation ΔH 0 of the products minus the sum of the standard enthalpies of formation of the reactants. You will also learn how to use this information to explain how to find the partial pressure of a gas collected over water. Calculate the standard enthalpy of combustion for the following reaction: C2H5OH(ℓ) + 7⁄2O2(g) ---> … & Learn what the common ion effect is, how to make equilibrium calculations involving it, and how to find the concentrations of ions when adding reactions in equilibrium to solutions that already contain ions. Terms In this lesson, you'll learn how varying the conditions of concentration, temperature, and pressure will affect the reactants and products in a chemical reaction at equilibrium. Learn how to represent single, double and triple bonds with lines instead of dots. Combustion of 3.65 of benzene causes a temperature rise of 4.41 C^o in a certain bomb calorimeter. How to Identify Chemicals in Solution: Test Methods & Materials. (b) Compare the quantity of heat… C = -393.5 h2 is 285.5. Using Sodium Hydroxide Solution to Identify Metal Ions. Standard heat of combustion: The energy liberated when a … Sciences, Culinary Arts and Personal Two scientists came to a conclusion: an acidic solution behaves as proton donors, which is in the form of a hydrogen ion. Review what a Lewis dot diagram is and discover how to draw a Lewis dot structural formula for compounds. Do you have a mysterious solution sitting around? A standard enthalpy of formation is an enthalpy change for a reaction in which … Calculate the enthalpy change for the formation benzene from the elements at 25 oC and one bar. This is what we call the Bronsted-Lowry definition of an acid, which is the main focus of this lesson. In this lesson, we will learn how to conduct these tests and interpret the results. Benzene causes central nervous system damage acutely and bone marrow damage chronically and is carcinogenic. Services, Using Hess's Law to Calculate the Change in Enthalpy of a Reaction, Working Scholars® Bringing Tuition-Free College to the Community, The standard heat of combustion of benzene is {eq}\Delta H=-3271\ \text{kJ/mol} {/eq}. This is one way to calculate the heat transferred, or enthalpy change, of a chemical reaction. Don't worry, this lesson will help you become a pro at all of these things by walking through two comprehensive problems that address all of these topics. Become a Study.com member to unlock this The standard enthalpy of formation of benzene, C6H6, is +49.2 kJ/mole. | Calculate its standard heat of formation, ? ?%, using the data: Hint: You need to write balanced equation for combustion of benzene. The standard heat of combustion of benzene is -3271 kJ/mol. Want to make sure you don't blow yourself up during a chemical reaction? The standard enthalpy of combustion of C2H6O(l) is -1,367 kJ mol-1 at 298 K. What is the standard enthalpy of formation of C2H6O(l) at 298 K? You will also discover how factors such as temperature, concentration, surface area, and catalysts impact reaction rates. In this lesson, you'll learn why disorder is the natural state of matter and how we can predict entropy change in a physical or chemical reaction. Predicting the Entropy of Physical and Chemical Changes. The mathematical expression of the change in enthalpy of a chemical reaction is shown below, {eq}\Delta H=\Delta {{H}_{p}}-\Delta {{H}_{r}} {/eq}.