Chemical Thermodynamics — Chemistry STD 12 Science — Question
Maharashtra BoardEnglish MediumSTD 12 ScienceChemistryChemical Thermodynamics3 Marks
Question
Define and explain the term, enthalpy or heat of reaction.
✓
Answer
Enthalpy or heat of reaction: The enthalpy of a chemical reaction is the difference between the sum of the enthalpies of products and that of the reactants with every substance in a definite physical state and in the amounts (moles) represented by the coefficients in the balanced equation. Explanation : Consider the following general reaction, $a A+b B \rightarrow c C+d D$ The heat of the reaction $\Delta H$ is the difference in sum of enthalpies of products and sum of enthalpies of reactants. $\begin{aligned} & \therefore \Delta H=\Sigma H_{\text {products }}-\Sigma H_{\text {reactants }} \\ & =\left[c H_C+d H_D\right]-\left[a H_A+b H_B\right] \\ & =\Sigma_P H-\Sigma_R Z \end{aligned}$ where $H$ represents enthalpy of the substance. For endothermic reaction, $\Delta H$ is positive, $(\Delta H>0)$. For exothermic reaction, $\Delta H$ is negative, $(\Delta H <0)$.
Need a full question paper?
Generate a complete, print-ready paper with questions like this in minutes — across 16+ boards, with answer keys.