• 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 $\Delta$U and $\Delta$H

• System, the part of the world in which is under study
• Surroundings, the region outside the system
• Boundary/Wall, a barrier between system and surroundings
• Thermodynamic systems
  • Open systems can exchange both matter and energy with the environment
  • Closed systems exchange energy but not matter with the environment
  • Isolated systems does not interact anyway with the surroundings

• Rigid - non-rigid / movable

$\quad\quad\quad\downarrow$

• mechanical exchange / Work
• Impermeable-permeable (matter is allowed to pass through it)

$\quad\downarrow\quad\quad\quad\quad\quad\quad\downarrow$

• closed system $\quad\quad$ material exchange

• Adiabatic - nonadiabatic / diathermic boundary (permits the passage of heat)

$\quad\quad\quad\downarrow$

• thermal exchange / Heat
• A system surrounded by a rigid, impermeable, adiabatic wall - Isolated system

• How do we define a system? state of a system
• Macroscopic state of a system can be specified by the values of a small number of macroscopic variables - properties/parameters / thermodynamic variables of a system

• Intensive properties do not depend upon size (the quantity of matter present) of the system at all pressure, temp, viscosity, density etc

• Extensive properties depend upon size of the system, mass, volume, surface area etc

• Homogenoeous system a system having uniform values of each intensive properties throughout - a single phase - solution / pure

• Heterogeneous system a system with more than one phase

• Phase- a homogeneous part of a system is called a phase

• Processes When one or more of the parameters of a system changes, the state of the system also changes and system is undergoing a process

• Isothermal (I), isobaric (p), isochoric (V)

• Cyclic

• Thermodynamic equilibrium
• For isolated system
  • Macroscopic properties do not change with time
• For Non isolated system
  • Macroscopic properties do not change with time
  • Removal of the system from contact with its surroundings causes no change in the properties of the system
  • A system in thermodynamic equilibrium is an equilibrium system
  • State of a thermodynamic only defined by the present values of the state variables not by the history

• Internal energy (U) - due to molecular motions + intermolecular interactions
• U = molecular traslation, rotational, vibrational, and electronic energies, +relativistic rest-mass energy, $m_{rest}$ C² of electrons ad the nuclei+potential energy of interaction between the molecules
• U =$f(T,V,n_1,n_2....)$
• $\Delta$U = f(T,V,)
• ideal gass U = f(T)
• $\Delta$U =f(T)

• $\Delta$E = $\Delta$U
• $\Delta$ K & $\Delta$ V = 0
• $\Delta$u = q + w
• If volume is fixed w=o, $\Delta$u = $q_v$
• Adiabatic process- q=0, $\Delta$u= $W_ad$
• An isolated w=0, q=0 , $\Delta$u = 0 $\rightarrow$ first law of thermodynamics

• $\Delta$u=q+w (closed system) first
• Increase in energy of the system due to heat exchange between system and surroundings across a non-adiabatic wall
• W = increase in energyu of the system due to exchange of energy as work between system and surroundings across a non-rigid wall
• An isolated system, $\Delta$u=0

• Force = $P_{ex}.A$
• Work done = force × distance
• $P_{ex}.A.l$
• $P_{ex}\Delta$v
• $P_{ex}(V_f-V_i)$
• W=-$P_{ex}(V_f-V_i)$

• For compression
• $\Delta$V= -ve
• $V_f<V_i$
• Surroundings does work on system as a result the energy of system goes up - w>0
• w = -$P_{ex}\Delta$V>0
• For expansion
• $\Delta$V= +ve
• w = -$P_{ex}\Delta$V < 0
• $\Delta$u= q-$P_{ex}\Delta$V - one step process

• $\omega$ depends on path which has bean adopted for going from state 1 to state 2
• $\Delta$U = q + w

• Reversible process
• Is a process where system is always infinisimally close to equilibrium, an infinisimal change in condition can reverse the process to restore both system and surroundings to the initial state
• $P_{ex}$ -P infinisimally small
• Infinisimally slow process - infinite time - idealized

• dw = -$P_{ex} dv$ ( $P_{ex}≈P$)
• dw =-pdv (reversible process)
• w = $\int^2_1$pdv = reversible process
• w = -$P_{ex}\Delta$V = irreversible process
• Ideal gas $p=\frac{nRT}{V}$
• w = $\int^{v_2}_{v_1}\frac{nRT}{V} dv \Rightarrow$ isothermal process
• $w = nRT\int^{v_2}_{v_1} \frac{dv}{V}$
• w = nRT $ln \frac{V_2}{V_1}$

• w = -nRT $ln\frac{V_2}{V_1}$
• $\Delta u = 0$ , q= -w
• Compression $V_2 < V_1, \quad w > 0$
• expansion $V_2 > V_1 , \quad w < 0$
• Free expansion
• $P_{ex} = 0$
• $w =-P_{ex} \Delta V = 0$
• isothermal process for ideal gas
• $\Delta V= 0$ , $q=0$

• $q=0$
• $\Delta u= w_{ad}$
• Isochoric process
• $\Delta V=0$ , $w=0$
• $\Delta u =q_v$

• Isobaric process, constant P process
• $\Delta u= q+w$
• $q_p - p\Delta v$
• $U_2-U_1 = q_p -p(V_2 -V_1)$
• $\therefore q_p = (U_2 + P_{v_2}) - (U_1 + P_{v_1})$
• New thermodynamic parameter $H = U + PV$
• enthalpy - "enthalpien" to work or heat content.....
• $\Delta H = H_2 -H_1$

• $q_p = (U_2 + P{V_2}) - ( U_1 + P{V_1})$
• $H = U + PV$
• $q_p = H_2 - H_1 = \Delta H$
• Heat absorbed by the system at constant p
• exothermic process,$\Delta H <0$
• endothermic process, $\Delta H > 0$
• $\Delta H = \Delta U + \Delta PV$
• for liquids and solids
• $\Delta H \approx \Delta U$

• $V_A$ = volumne of reactant, $n_A$
• $V_B$ = volumne of poducts, $n_B$
• $PV_A = n_A RT$
• $PV_B = n_B RT$
• $PV_B - PV_A = n_B RT - n_A RT$
• $P(V_B-V_A) = (n_B-n_A)RT$
• $P(\Delta V) = \Delta n_g RT$
• $\Delta H = \Delta V + \Delta n_g RT$