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The standard enthalpy of formation (∆fHº298) for methane, CH4 is– 74.9 kJ mol–1. In order to calculate the average energy given out in the formation of a C–H bond from this it is necessary to know which one of the following?
  • a)
    the dissociation energy of the hydrogen molecule, H2
  • b)
    the first four ionisation energies of carbon
  • c)
    the dissociation energy of H2 and enthalpy of sublimation of carbon (graphite)
  • d)
    the first four ionisation energies of carbon and electron affinity of hydrogen
Correct answer is option 'C'. Can you explain this answer?
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The standard enthalpy of formation (fHº298) for methane, CH4 is&n...
Write the expression of the balanced chemical equation for the formation of methane.

If the values of enthalpy of sublimation of carbon and bond dissociation energy of H2 are known, the average energy released in the given reaction can be calculated.
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The standard enthalpy of formation (fHº298) for methane, CH4 is&n...
°) of a compound is the change in enthalpy that occurs when one mole of the compound is formed from its constituent elements in their standard states under standard conditions (25°C and 1 atm pressure). The standard enthalpy of formation is usually denoted as ΔfH°.

For example, the standard enthalpy of formation of water (H2O) is -285.83 kJ/mol. This means that when one mole of water is formed from its constituent elements (hydrogen and oxygen) under standard conditions, 285.83 kJ of heat is released.

Standard enthalpy of formation values are useful in calculating the enthalpy changes of chemical reactions. By subtracting the enthalpies of formation of the reactants from the enthalpies of formation of the products, we can determine the overall enthalpy change of the reaction.

It is important to note that the standard enthalpy of formation values are only valid at standard conditions. At different temperatures and pressures, the enthalpy of formation will be different.
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Properties, whose values depend only on the concentration of solute particles in solution and not on the identity of the solute are called colligative properties. There may be change in number of moles of solute due to ionisation or association hence these properties are also affected. Number of moles of the product is related to degree of ionisation or association by vant Hoff factor ‘i’ given by i = [ 1 + (n – 1) α] for dissociationwhere n is the number of products (ions or molecules) obtained per mole of the reactant & i = for association.Where n is number of reactant particles associated to give 1 mole product.A dilute solution contains ‘t’ moles of solute X in 1 Kg of solvent with molal elevation constant Kb. The solute dimerises in the solution according to the following equation. The degree of association is α.Q.The vant Hoff factor will be [ if we start with one mole of X ]

Properties, whose values depend only on the concentration of solute particles in solution and not on the identity of the solute are called colligative properties. There may be change in number of moles of solute due to ionisation or association hence these properties are also affected. Number of moles of the product is related to degree of ionisation or association by vant Hoff factor ‘i’ given by i = [ 1 + (n – 1) α] for dissociationwhere n is the number of products (ions or molecules) obtained per mole of the reactant & i = for association.Where n is number of reactant particles associated to give 1 mole product.A dilute solution contains ‘t’ moles of solute X in 1 Kg of solvent with molal elevation constant Kb. The solute dimerises in the solution according to the following equation. The degree of association is α.Q.The colligative properties observed will be

Properties, whose values depend only on the concentration of solute particles in solution and not on the identity of the solute are called colligative properties. There may be change in number of moles of solute due to ionisation or association hence these properties are also affected. Number of moles of the product is related to degree of ionisation or association by vant Hoff factor ‘i’ given by i = [ 1 + (n – 1) α] for dissociationwhere n is the number of products (ions or molecules) obtained per mole of the reactant & i = for association.Where n is number of reactant particles associated to give 1 mole product.A dilute solution contains ‘t’ moles of solute X in 1 Kg of solvent with molal elevation constant Kb. The solute dimerises in the solution according to the following equation. The degree of association is α.Q.The equilibrium constant for the process can be expressed as

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The standard enthalpy of formation (fHº298) for methane, CH4 is– 74.9 kJ mol–1. In order to calculate the average energy given out in the formation of a C–H bond from this it is necessary to know which one of the following?a)the dissociation energy of the hydrogen molecule, H2b)the first four ionisation energies of carbonc)the dissociation energy of H2 and enthalpy of sublimation of carbon (graphite)d)the first four ionisation energies of carbon and electron affinity of hydrogenCorrect answer is option 'C'. Can you explain this answer?
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The standard enthalpy of formation (fHº298) for methane, CH4 is– 74.9 kJ mol–1. In order to calculate the average energy given out in the formation of a C–H bond from this it is necessary to know which one of the following?a)the dissociation energy of the hydrogen molecule, H2b)the first four ionisation energies of carbonc)the dissociation energy of H2 and enthalpy of sublimation of carbon (graphite)d)the first four ionisation energies of carbon and electron affinity of hydrogenCorrect answer is option 'C'. Can you explain this answer? for JEE 2024 is part of JEE preparation. The Question and answers have been prepared according to the JEE exam syllabus. Information about The standard enthalpy of formation (fHº298) for methane, CH4 is– 74.9 kJ mol–1. In order to calculate the average energy given out in the formation of a C–H bond from this it is necessary to know which one of the following?a)the dissociation energy of the hydrogen molecule, H2b)the first four ionisation energies of carbonc)the dissociation energy of H2 and enthalpy of sublimation of carbon (graphite)d)the first four ionisation energies of carbon and electron affinity of hydrogenCorrect answer is option 'C'. Can you explain this answer? covers all topics & solutions for JEE 2024 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for The standard enthalpy of formation (fHº298) for methane, CH4 is– 74.9 kJ mol–1. In order to calculate the average energy given out in the formation of a C–H bond from this it is necessary to know which one of the following?a)the dissociation energy of the hydrogen molecule, H2b)the first four ionisation energies of carbonc)the dissociation energy of H2 and enthalpy of sublimation of carbon (graphite)d)the first four ionisation energies of carbon and electron affinity of hydrogenCorrect answer is option 'C'. Can you explain this answer?.
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