Duration: 3:52

3 views

0

The change in internal energy \( (U) \) can be brought about in two ways:
(i) Either by allowing the heat to flow into the system or out of the system
(ii) By doing work on the system or the work done by the system
Using the symbol \( q \) to represent heat transferred to system and using work done by the system \( -w \), we can represent the internal energy change of a system, \( \Delta U \), as :
\[
q=\Delta U+(-w)
\]
(First law of thermodynamics)
If the reaction is carried out in a closed container with constant volume, so that \( \Delta V=0 \)
Hence,
\[
q_{v}=\Delta U
\]
On the other hand, if a reaction is carried out in open vessel that keeps the pressure constant and allows the volume of the system to change freely. In such case, \( \Delta V \neq 0 \) and \( -w=P \cdot \Delta V \).
Hence,
\[
\begin{array}{l}
q_{p}=\Delta U+P \Delta V \\
q_{p}=q_{v}+\Delta n_{g} R T
\end{array}
\]
\[
\text { Also, } \quad q_{p}=q_{v}+\Delta n_{g} R T
\]
As reactions carried out at constant pressure are so common, the heat change for such process is given a special symbol \( \Delta H \), called the enthalpy change of the reaction. The enthalpy \( (H) \) of the system is the name given to the quantity \( (U+P V) \).
In which of the following cases \( \Delta H \) and \( \Delta U \) are not equal to each other?
(A) The reaction involves no gaseous reactant and product
(B) The number of moles of gaseous reactants and gaseous products is not equal to each other
(C) The number of moles of gaseous reactants and gaseous products is equal to each other
(D) The process is carried out in closed vessel
📲PW App Link - https://bit.ly/YTAI_PWAP
🌐PW Website - https://www.pw.live