Chemistry > Thermodynamics and Thermochemistry > 9.0 Enthalpy $(H)$ or Heat Content
Thermodynamics and Thermochemistry
1.0 Introduction to Thermodynamics
1.1 Importance of Thermodynamics
1.2 Limitations of Thermodynamics
1.3 Some Basic Terms of Thermodynamics
2.0 Thermodynamic Processes
2.1 Some other important relations of adiabatic process
2.2 Reversible and Irreversible Processes
2.3 Polytropic Process
3.0 Heat $(Q)$
4.0 Work $(W)$
5.0 Internal Energy
6.0 Zeroth Law of Thermodynamic
7.0 First Law of Thermodynamics
8.0 Heat Capacity
9.0 Enthalpy $(H)$ or Heat Content
10.0 Significance of $?H$ and $?E$
11.0 Relationship Between $?H$ and $?E$
12.0 Standard Enthalpy of Reaction
12.1 Molar Enthalpy of Fusion $\left( {\Delta {H_{fus}}} \right)$
12.2 Molar Enthalpy of Vaporisation $(\Delta {H_{vap}})$
12.3 Enthalpy of Sublimation $\left( {\Delta {H_{sub}}} \right)$
12.4 Enthalpy of Formation
12.5 Enthalpy of Combustion $\left( {\Delta {H_c}} \right)$
12.6 Enthalpy of Neutralization $\left( {\Delta {H_{neu}}} \right)$
12.7 Enthalpy of Solution $\left( {\Delta {H_{sol}}} \right)$
13.0 Law of Thermodynamics
14.0 Bond Energy or Bond Enthalpies
15.0 Second Law of Thermodynamic
16.0 Entropy (S)
16.1 Some Important points Related to Entropy
16.2 Entropy Change in Various Thermodynamic Process
16.3 Entropy Change in Phase Transformation
17.0 Spontaneous Processes
18.0 Free Energy (G)
19.0 Enthalpy, Entropy, Free Energy Changes and The Nature of Process
20.0 Standard Free Energy Change
21.0 Coupled Reactions
22.0 Third Law of Thermodynamic
22.1 Third Law of Thermodynamics, Entropy ? Temperature
22.2 Limitations of Third Law of Thermodynamics
23.0 Important Facts
9.1 Enthalpy Change
1.2 Limitations of Thermodynamics
1.3 Some Basic Terms of Thermodynamics
2.2 Reversible and Irreversible Processes
2.3 Polytropic Process
12.2 Molar Enthalpy of Vaporisation $(\Delta {H_{vap}})$
12.3 Enthalpy of Sublimation $\left( {\Delta {H_{sub}}} \right)$
12.4 Enthalpy of Formation
12.5 Enthalpy of Combustion $\left( {\Delta {H_c}} \right)$
12.6 Enthalpy of Neutralization $\left( {\Delta {H_{neu}}} \right)$
12.7 Enthalpy of Solution $\left( {\Delta {H_{sol}}} \right)$
16.2 Entropy Change in Various Thermodynamic Process
16.3 Entropy Change in Phase Transformation
22.2 Limitations of Third Law of Thermodynamics
$H = E +PV$
$?H = ?E + ?(PV)$
$?H = ?E + ? PV+ P?V$
At constant pressure
$?H = ?E + P?V$
It is an extensive property and state function.
The enthalpy change $?H$ i.e., increase in enthalpy $H$ is equal to heat absorbed at constant pressure and this explains the name 'heat content' for the function $H.$
At constant pressure small amount of heat transfer
$(dq)P$ $=$ $dH$ $ = n{C_p}dT$
Where
n $=$ no. of moles
${C_p} = $ molar specific heat at constant pressure
$dT =$ small change in temperature
At constant temperature and pressure
$\Delta H = \Delta E + P\Delta V,\Delta E = $ Change in internal energy
$P\Delta V = \Delta W = $ Work done
(1) Most of the chemical reactions occur at constant pressure (1 atmospheric) and in an open vessel.
(2) When
$\Delta V = 0{\text{ }}\Delta H = \Delta E$
$\Delta H = - ve,$ (reaction is exothermic)
$\Delta H = + ve,$ (reaction is endothermic)
(3) Enthalpy of a system depends on the physical state (solid, liquid and gas)
(4) $H$ is a state function. Therefore, it depends only on initial and final states. The absolute value of enthalpy cannot be determined
(5) Enthalpy of monoatomic gas $ = \frac{5}{2}RT$ per mole.
(6) Change in enthalpy of the products and reactants at $298 K$ and $1$ atmospheric pressure is called standard molar enthalpy change.
