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Thermochemistry MCQ - Practice Questions with Answers

Edited By admin | Updated on Sep 25, 2023 25:23 PM | #NEET

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  • Thermochemistry And Enthalpy For Chemical Reaction is considered one of the most asked concept.

  • 18 Questions around this concept.

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Consider an endothermic reaction X\rightarrow Y with the activation energies E_{b}\: and\: E_{f} for the backward and forward reactions, respectively. In general

From the following bond energies:

H-H bond energy : 431.37 k J  mol^{-1}

C=C bond energy : 606.10 k J  mol^{-1}

C-C bond energy : 336.49 k J  mol^{-1}

C-H bond energy : 410.50 k J  mol^{-1}

Enthalpy for the reaction,

 

 

Which of the following options is the correct relation between change in enthalpy and change in internal energy?

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Concepts Covered - 1

Thermochemistry And Enthalpy For Chemical Reaction

Thermochemistry

It deals with the heat changes during chemical reactions. It is called chemical energetics and based on first law of thermodynamics. It is called as chemical energetics and based on first law of thermodynamics.

Exothermic Reaction

\begin{array}{l}{\text { Heat is evolved here. }} \\ {\Delta \text {H is -ve as } \mathrm{H}_{\mathrm{R}}>\mathrm{H}_{\mathrm{P}}} \\ {\mathrm{\Delta H}=\mathrm{H}_{\mathrm{P}}-\mathrm{H}_{\mathrm{R}}=-\text { ve } \quad \text { (at constant pressure) }} \\ {\text { At constant volume, }} \\ {\Delta \mathrm{E}=\left(\mathrm{E}_{\mathrm{P}}-\mathrm{E}_{\mathrm{R}}\right)=-\mathrm{ve}} \\ {\text { that is. } \mathrm{E}_{\mathrm{R}}>\mathrm{E}_{\mathrm{P}}}\end{array}

Endothermic Reaction

\begin{array}{l}{\text {Here heat is absorbed. }} \\ { \Delta H \text { or } \Delta E=+\text { ve for endothermic }} \\ {\Delta H=H_{p}-H_{R}=+\text { ve }(\text { at constant pressure as })} \\ {\text { as } H_{p}>H_{R} \text { or } E_{p}>E_{R}} \\ {\text { At constant volume }} \\ {\Delta E=\left(E_{p}-E_{R}\right)=+v e}\end{array}

Heat or Enthalpy of Reaction

It is the change in enthalpy (amount of heat evolved or absorbed) when the number of gm-moles of the substance indicated by a chemical reaction have undergone complete reaction.

\begin{array}{l}{\text { It is determined by water and Bomb calorimeters. }} \\ {\text { Mathematically, it is given as }} \\ {=\Sigma \mathrm{H}_{\mathrm{p}}-\Sigma \mathrm{H}_{\mathrm{R}}} \\ {\text { It can be express by }[\mathrm{AH}]_{\mathrm{p}} \text { or }[\Delta \mathrm{E}]_{\mathrm{v}} \text { at constant }} \\ {\text { pressure and volume respectively. }}\end{array}

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Thermochemistry And Enthalpy For Chemical Reaction

Chemistry Part I Textbook for Class XI

Page No. : 174

Line : 50

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