Chemistry, asked by nihalmishra55, 1 year ago

what is hess law of constants heat summation ? give an example to explaine the law

Answers

Answered by Anonymous

$\textsf{\underline {\Large {Hess's Law of Constant Heat Summation :}}}$

$\textsf{\underline {The basis of Hess's law is that enthalpy is a state function.}}$

According to this law, the change in enthalpy remains constant whether the process is carried out in one step or in more than one step.

$\textsf{\underline {\large{Applications of Hess Law}}}$ :

1. Calculation of enthalpy of formation.

2. Calculation of $\mathsf{_{c}H}$ .

3. Calculation of Enthalpy of reaction.

4. Calculation of enthalpy of allotropic transformation.

$\textsf{\large{\underline {Example}}}$ :

Let 's consider this law by the formation of $\mathsf{CO_2}$ and $\mathsf{O_2}$

$\mathsf{\underline {Way\: 1}}$ : $\mathsf{C(s) \:+\:O_2(g)\:{\rightarrow{CO_2(g)}}}$

$\Delta{\mathsf{_{r}{H}^{\circ}\:=\:-393.5\:kJ}}$

$\mathsf{\underline {Way \:2}}$ : $\mathsf{C(s) \:+\:{\dfrac{1}{2}O_2(g)\:{\rightarrow{CO(g)}}}}$

$\Delta{\mathsf{_{r}H_{1}^{\circ}\:=\:-110.5\:kJ}}$

$\mathsf{CO(g) \:+\:{\dfrac{1}{2}O_2(g)\:{\rightarrow{CO_2(g)}}}}$

$\Delta{\mathsf{_{r}H_{2} ^{\circ}\:=\:-283.0\:kJ}}$

$\boxed{\mathsf{C(s) \:+\:O_2(g)\:{\rightarrow{CO_2(g)}}}}$

$\Delta{\mathsf{_{r}{H}^{\circ}\:=\:-393.5\:kJ}}$

➡️ $\boxed{\Delta{\mathsf{H\:=\:{\Delta{H_1}\:+\:{\Delta{H_2}}}}}}$