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Standard Enthalpy Of Formation, Combustion And Bond Dissociation MCQ - Practice Questions with Answers
Edited By admin | Updated on Sep 25, 2023 25:23 PM | #NEET
Quick Facts
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Enthalpy Of Combustion, Enthalpy Of Dissociation, Atomisation And Phase Change is considered one of the most asked concept.
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30 Questions around this concept.
Solve by difficulty
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?
If the bond energies of $\mathrm{H}-\mathrm{H}, \mathrm{Br}-\mathrm{Br}$ and $\mathrm{H}-\mathrm{Br}$ are 433,192 and $364 \mathrm{~kJ} \mathrm{~mol}^{-1}$ respectively, the $\Delta H^{\circ}$ for the reaction
$H_{2(g)}+B r_{2(g)} \rightarrow 2 H B r(g)$ is
Bond dissociation enthalpy of ,
and
are 434, 242, and 431 kJ
respectively. Enthalpy formation of HCl is:
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Enthalpy change for reaction
$4 H_{(g)} \rightarrow 2 H_{2(g)}$ is $869.6 K J$
The dissociation energy of H-H bond is?
Which one of the following orders is correct for the bond dissociation enthalpy of halogen molecules?
Concepts Covered - 2
Enthalpy Of Combustion
Heat of Combustion
1. It is, changes in enthalpy when one mole of a substance is completely oxidized or combusted or burnt.
2. is - ve here as heat in always evolved here that is, exothermic process.
3. Heat of combustion is useful in calculating the calorific value of food and fuels.
4. It is also useful in confirming structure of organic molecules having C,H,O,N etc.
5. Enthalpy change by combustion of 1 gm solid or 1 gm liquid or 1 cc gas is called calorific value.
Enthalpy Of Dissociation, Atomisation And Phase Change
Enthalpy of Dissociation or Ionization
It is defined as, "The quantity of heat absorbed when one mole of a substance is completely dissociated into its ions". Example,
Heat of Atomization
It is the enthalpy change (heat required) when bonds of one mole of a substance are broken down completely to obtain atoms in the gaseous phase (isolated) or it is the enthalpy change when one mole of atoms in the gas phase is formed from the corresponding element in its standard state. In case of diatomic molecules, it is also called bond dissociation enthalpy.
Phase Transition and Transition Energy
- The change of matter from one state (solid, liquid or gas) to another state is called Phase Transition.
- Such changes occur at definite temperatures such as meltmg point (solid to liquid), bolling point (liquid to vapours) etc., and are accompanied by absorption or evolution of heat. The enthalpy change during such phase transitions is called heat of transltion or transition energy.
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