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Chemical Thermodynamics — Chemistry STD 12 Science — Question

Maharashtra BoardEnglish MediumSTD 12 ScienceChemistryChemical Thermodynamics4 Marks
Question
Distinguish between Endothermic reaction and Exothermic reaction.
✓

Answer

Endothermic reaction:
  • In endothermic reaction heat is absorbed from suroundings.
  • Sum of enthalpies of products is greater than sum of enthalpies of reactants i.e.$\Sigma_P H>\Sigma_R H$ 
  • Heat of reaction, ΔH is positive.
  • Products are less stable than reactants.
  • $\begin{aligned} & C _{( s )}+ O _{2( g )} \rightarrow CO _{2( g )} \\
    & \Delta H =-394 kJ \end{aligned}$
  • This reaction requires supply of thermal energy.
Exothermic reaction:
  • In exothermic reaction heat is given out to surroundings.
  • Sum of enthalpies of products is less than sum of enthalpies of reactants.
    i.e. $\Sigma_P H<\Sigma_R H$
  • Heat of reaction, ΔH is negative.
  • Products are more stable than reactants.
  • $\begin{aligned} & N _{2( g )}+ O _{2( g )} \rightarrow 2 NO \\ & \Delta H =+180 kJ \end{aligned}$
  • This reaction does not require supply of thermal energy.

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