Question

Derive the relation between ru and rh for a chemical reaction. How is this relation given for the condensed phases and ideal gases?

Answer 1

Ok
Ok
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Brainliest

Answer 2

Explanation:

According to the enthalpy equation:

$H=U+P V \rightarrow(1)$

Differentiating the equation (1)  we get,

$\Delta H=\Delta U+P \Delta V+V \Delta P \rightarrow(2)$

During chemical reaction the external pressure will be constant.

Hence, $\Delta P=0$

Thus equation (2) will be $\Delta H=\Delta U+P \Delta V \rightarrow(3)$

The ideal gas behaviour of the reactants and products will be  

For reactants, $P V_{r}=n_{r} R T \rightarrow(4)$

For products, $P V_{p}=n_{P} R T \rightarrow(5)$

Now substituting equation (4)  from equation (3) then we get,

$P\left(V_{p}-V_{r}\right)=\left(n_{p}-n_{v}\right) R T$

$P \Delta V=\Delta n_{g} R T$ for ideal gas

$\Delta H=\Delta U+\Delta n_{g} R T$

$\Delta n_{g}$=No. of moles of  gaseous products – No. of moles of gaseous reactants

For condensed phase $\Delta n_{g}$=0

Hence, $\Delta H=\Delta U$ for condensed gases.