Hess's Law of Constant Heat Summation

Given that, the molar combustion enthalpy of benzene, cyclohexane and hydrogen are $\mathrm{x}, \mathrm{y}$ and $\mathrm{z}$, respectively, the molar enthalpy of hydrogenation of benzene to cyclohexane is

Hess's law of constant heat of summation states that regardless of the multiple stages or steps of a reaction the total enthalpy change of the reaction is the sum of all changes.

Calculate the enthalpy of hydrogenation of ethylene from the following data. Bond energies of $\mathrm{C}-\mathrm{H},$ $\mathrm{C}-\mathrm{C}$ , $\mathrm{C}=\mathrm{C}$ and $\mathrm{H}-\mathrm{H}$ are $414, 347, 618$ and $435$ ${\mathrm{kJmol}}^{-1}$.

State and explain Hess's Law of constant heat summation.
 

Consider the chemical reaction, ${\mathrm{OF}}_2 \left(\mathrm{g}\right)+ {\mathrm{H}}_2\mathrm{O} \left(\mathrm{g}\right) \to {\mathrm{O}}_2 \left(\mathrm{g}\right) + 2\mathrm{HF} \left(\mathrm{g}\right), △\mathrm{H}° =-323 \mathrm{kJ}$. What is $△\mathrm{H}°$ of the reaction if direction of reaction is reversed?

Consider the chemical reaction, ${\mathrm{OF}}_2 \left(\mathrm{g}\right)+ {\mathrm{H}}_2\mathrm{O} \left(\mathrm{g}\right) \to {\mathrm{O}}_2 \left(\mathrm{g}\right) + 2\mathrm{HF} \left(\mathrm{g}\right), △\mathrm{H}° =-323 \mathrm{kJ}$. What is $△\mathrm{H}°$ of the reaction if the equation is multiplied by $3$.

Enthalpies of formation of CO(g), CO₂(g), N₂O(g) and N₂O4(g) are -110, -393, 81 and 9.7 kJ mol^-1 respectively. Find the value of ${\Delta }_{\text{r}}\text{H}$ for the reaction N₂O₄(g) + 3 CO(g) $⟶$ N₂O(g) + 3CO₂ (g)

Silanes are silicon hydrides of general formula $\mathrm{S}{\mathrm{i}}_{\mathrm{n}}{\mathrm{H}}_{2\mathrm{n}+2}$ and have several applications. From the data given below, the bond dissociation enthalpy of $\mathrm{Si}-\mathrm{Si}$bond (in $\mathrm{k}\mathrm{J}\mathrm{m}\mathrm{o}{\mathrm{l}}^{-1}$ ) is

Given:

$∆\mathrm{H}$ of the reaction $2\mathrm{S}\mathrm{i}\left(\mathrm{s}\right)+3{\mathrm{H}}_2\left(\mathrm{g}\right)\to \mathrm{ }\mathrm{S}{\mathrm{i}}_2{\mathrm{H}}_6\left(\mathrm{g}\right)$ is $80.3 \mathrm{k}\mathrm{J}\mathrm{m}\mathrm{o}{\mathrm{l}}^{-1}$

Bond dissociation enthalpy for $\mathrm{H} - \mathrm{H} = 436 \mathrm{k}\mathrm{J}\mathrm{m}\mathrm{o}{\mathrm{l}}^{-1}$

Bond dissociation enthalpy for $\mathrm{Si} - \mathrm{H} = 304 \mathrm{k}\mathrm{J}\mathrm{m}\mathrm{o}{\mathrm{l}}^{-1}$

${\mathrm{\Delta }}_{\mathrm{f}}\mathrm{H}\mathrm{ }\left[\mathrm{S}\mathrm{i}\left(\mathrm{g}\right)\right]=405\mathrm{ }\mathrm{k}\mathrm{J}\mathrm{m}\mathrm{o}{\mathrm{l}}^{-1}$

(Note: Report your answer after rounding up to the nearest integer value.)

The bond dissociation energies for $\mathrm{C}{\mathrm{l}}_2$ , ${\mathrm{I}}_2$ and $\mathrm{I}\mathrm{C}\mathrm{l}$ are $242.3$ , $151$ and $211.3\mathrm{}\mathrm{k}\mathrm{J}/\mathrm{m}\mathrm{o}\mathrm{l}$ respectively. The enthalpy of sublimation of iodine is $62.8 \mathrm{k}\mathrm{J}/\mathrm{m}\mathrm{o}\mathrm{l}$ . What is the standard enthalpy of formation of $\mathrm{I}\mathrm{C}\mathrm{I} \left(\mathrm{g}\right)$ ?

The statement “The change of enthalpy of a chemical reaction is same whether the reaction takes place in one or several steps” is

If enthalpy of an overall reaction $\mathrm{X}\to \mathrm{Y}$ along one route is ${∆}_{\mathrm{r}}\mathrm{H}$ and ${∆}_{\mathrm{r}}{\mathrm{H}}_1$ , ${∆}_{\mathrm{r}}{\mathrm{H}}_2$ , ${∆}_{\mathrm{r}}{\mathrm{H}}_3$ …representing enthalpies of reactions leading to same product $\mathrm{Y}$ then ${∆}_{\mathrm{r}}\mathrm{H}$ is

Hess’s law is applicable to heat of

Consider the following reaction

$C+O_2\to C{O}_2$ $\Delta H_1=x$ $\dots \left(i\right)$

$C+\frac{1}{2}{O}_2\to CO$ $\Delta H_2=y$ $\dots \left(ii\right)$

$CO+\frac{1}{2}{O}_2\to C{O}_2$ $\Delta H_3=z$ $\dots \left(iii\right)$

What is the relation between $x,y,z$

Given, $S+\frac{3}{2}{O}_2\to S{O}_3+2x kcal$

$S{O}_2+\frac{1}{2}{O}_2\to S{O}_3+y kcal$

with the help of above reactions, find out the heat of formation of $S{O}_2.$

Given that

$C_{\left(s\right)}+O_{2\left(g\right)}\to C{O}_{2\left(g\right)};\mathrm{\Delta }{H}^o= -xkJ$

$2C{O}_{\left(g\right)}+O_{2\left(g\right)}\to 2C{O}_{2\left(g\right)};\mathrm{\Delta }{H}^o= -ykJ$

The enthalpy of formation of CO will be

What is the enthalpy change for $2{\mathrm{H}}_2{\mathrm{O}}_2\left(1\right)\to 2\mathrm{ }{\mathrm{H}}_2\mathrm{O}\left(1\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)$ if heat of formation of ${\mathrm{H}}_2{\mathrm{O}}_2\left(1\right)\mathrm{ }\mathrm{n}\mathrm{a}\mathrm{d}\mathrm{ }{\mathrm{H}}_2\mathrm{O}\left(1\right)\mathrm{ }\mathrm{a}\mathrm{r}\mathrm{e}-188\mathrm{ }\mathrm{a}\mathrm{n}\mathrm{d}-286\frac{\mathrm{k}\mathrm{J}}{\mathrm{m}\mathrm{o}{\mathrm{l}}^{-1}}$ respectively?

The values of heat of formation of $\mathrm{S}{\mathrm{O}}_2\mathrm{ }\mathrm{a}\mathrm{n}\mathrm{d}\mathrm{ }\mathrm{S}{\mathrm{O}}_3$ are $-298.2\mathrm{ }\mathrm{K}\mathrm{J}\mathrm{ }\mathrm{a}\mathrm{n}\mathrm{d}-98.2\mathrm{ }\mathrm{K}\mathrm{J}.$ The heat of formation of the reaction

$\mathrm{S}{\mathrm{O}}_2+\left(\frac{1}{2}\right){\mathrm{O}}_2\to \mathrm{S}{\mathrm{O}}_3\mathrm{ }$ will be

${\mathrm{H}}_2\left(\mathrm{g}\right)+{\mathrm{I}}_2\left(\mathrm{s}\right)\to 2\mathrm{H}\mathrm{I}\left(\mathrm{g}\right)$ ; $∆\mathrm{H}=51.9\mathrm{ }\mathrm{K}\mathrm{J}/\mathrm{m}\mathrm{o}\mathrm{l}\mathrm{e}$

${\mathrm{H}}_2\left(\mathrm{g}\right)+{\mathrm{I}}_2\left(\mathrm{g}\right)\to 2\mathrm{ }\mathrm{H}\mathrm{I}\left(\mathrm{g}\right)$ ; $∆\mathrm{H}=-9.2\mathrm{ }\mathrm{K}\mathrm{J}/\mathrm{m}\mathrm{o}\mathrm{l}\mathrm{e}$ . The heat of reaction of ${\mathrm{I}}_2\left(\mathrm{s}\right)\to {\mathrm{I}}_2\left(\mathrm{g}\right)$