• Essential concepts and definitions
• Heat, work & energy, internal energy
• First law of thermodynamics
• Calculation of work, heat in different process for an ideal gas
• Enthalpy and heat capacity
• Determination of $\Delta \mathrm{U}$ and $\Delta \mathrm{H}$

• Change in enthalpy in different processes / reaction
  • Enthalpy of reaction
  • Enthalpy of formation
  • Enthalpy of phase transition
  • Enthalpy of other processes / reactions
• Criteria for spontaneous process
  • Entropy
  • Gibbs free energy

• $\Delta_r H=$ total enthalpy of the product - total enthalpy of reactants
• $H_R=$ total enthalpy of reactants
• $H_p=$ total enthalpy or products
• At temp T
• $\Delta r H^0=\sum a_i H_m^0$ (Products) -$\sum b_i H_m^0$ (reactants)
• $\Delta r H^0=\sum a_i \Delta_f H^{\circ}$ (Products) -$\sum b_i \Delta_f H^{\circ}$ (reactants)

• $\Delta_r H^\circ = \sum \text{bond enthalpies (reactants)} - \sum \text{bond enthalpies (products)}$(gaseous reactions)
• $\Delta_f H^\circ (T)$, $\Delta_{\text {trs }} H^0(T)$
• $\Delta_{\text {fus }} H^{\circ}(T)$, $\Delta_{\text {vap }} H^{\circ}(T)$
• $\Delta_{\text {sub }} H^{\circ}(T)$, $\Delta_C H^{\circ}(T)$
• $\Delta_a H^{\circ}(T)$,$\Delta_{\text {Sub }} H^{\circ}(T)$
• $\Delta_r H^{\circ} \text { (ionization enthelphy) }$ and $\Delta_{r H^{\circ}} \text { (electron gain)}$
• These all are intensive quantities
• Thermochemical equation, Hess's law ,[Born - Haber cycle]
• $\Delta H$ is a state function it does not depend on the path

• 1st law - When one form of energy is converted to another, the total energy is conserved
• $\Delta v=0$ isolated
• $\Delta u=q+w$ closed system
• $q(\text { system })=-10J$
• $q(\text { surrounding })=+10J$
• $q(\text { total})=0J$
• Does not say
• Wheather the energy transfer will happen?
• which direction?
• How long?
• How fast? $\Rightarrow$ not part of thermodynamics , it is a part of kinetics.

• We know some processes happens spontaneously
• Spreading of perfume
• Gas expand into vaccum
• Hot object in a surrounding which has lower temperature , then the object will cool down
• A weight falls from a height
• On ignition - a fuel burns spontaneously
• Spontaneous processes are irreversible processes

• Spontaneous process means that the process has a tendency/potential to occur without any assistance from extrenal agency

• work have to be done to bring it about

• Non - spontaneous process-will not happen without any assistance from external energy

• Spontaneous process is an irreversible process which can only be reversed only by doing work

• Reverse - non-spontaneous process

• Energy decreases
• $\frac{1}{2} N_2(g)+\frac{3}{2} H_2(g) \rightarrow NH_3(g)$
• $\Delta r_H^{\circ}=-46.1 \mathrm{~kJ} \mathrm{mol}^{-1}$
• Decrease in energy can not be considered for spontaneity

• Mixing of ideal gases $\Rightarrow$ spontaneous

• $\frac{1}{2} \mathrm{N}_2(\mathrm{g})+\mathrm{O}_2(g) \rightarrow \mathrm{NO}_2(g)$

• $\Delta rH^\circ = +33.2 , \mathrm{kJ , mol^{-1}}$

• What is the criteria for Spontaneity?

• matter / energy is getting dispersed

• system + Surroundings $\rightarrow$ together is more random

• Natural tendency is to disperse/randomise/ become disordered

• Quantify randomness $\rightarrow$

• we introduce a thermodynamic parameter

• Entropy (S)

• for any spontaneous process the value of entropy of system + entropy of surroundings will increase

• $\Delta S_{\text {system }}+\Delta S_{\text {surrounding }}>0$

• isolated System

• $\Delta S_{\text {system }}>o$

• 2nd law thermodynamics

• $S$ - extensive state function
• $\Delta S$ - independent of path
• we will try to get the value of S
• If we add some energy as heat, entropy increases
• q - only appears during a process
• $q$ should be related to $\Delta s$
• $q>0, \Delta s>0$

• $T_1>T_2$

  • $q_{sys } < 0 \Delta S_{system} < 0$
  • $q_{surr }>0 \Delta S_{surr} > 0$
  • $q_{sys}+q_{surr}=0$
  • if $\Delta S$ is only related to q
  • $\Delta S = O$

• $\Delta S_total > 0$

  • $|\Delta S_{system}|<\Delta S_{surr}|$
  • $\Delta S \propto \frac{1}{T}$
  • $T_1>T_2$

• $\Delta S=\frac{q_{\text {rev }}}{T}$

• $\frac{q_{\text {rev }}}{T}$: energy transfer to system reversibly

• T: temperature in K

• Entorpy?

  • liq $\rightarrow$ gas $\Delta S_{sys}>0$
  • liq $\rightarrow$ solid $\Delta S_{sys}<0$

• (water)

  • $125^{\circ} \mathrm{C} \quad$ water $\rightarrow$ vapour (endothermic)
  • $-25^{\circ} \mathrm{C}$ water $\rightarrow$ ice (exothermic)

• Increasing the temp of a solid from 10K $\rightarrow$ 120K
• disorderd
• entropy increases ; $\Delta S>0$

- 2 $NaHCO_3$(s) $\rightarrow \mathrm{Na}_2 \operatorname{CO} 3(s)+\mathrm{CO}_2(s)+\mathrm{H}_2 \mathrm{O}(\mathrm{s})$

• $\Delta S>0$

• Spontaneity $\Delta S_{sys} +\Delta S_{surr}>o$