Fundamentals of thermodynamics:- 1st law, 2nd law and 3rd law short notes

·         Deals with energy and the energy changes.

Thermodynamics can only give information about a system when it is at equilibrium state; a time-invariant state.

When it is based on the concept of equilibrium it’s known as “Equilibrium thermodynamics”.

When it is based on the concept of time-invariant state it’s known as “Thermodynamics of Steady state” or “non-equilibrium thermodynamics”.

Equilibrium thermodynamics: - Only with closed and isolated systems.

System

·         Open: Both matter and energy can transfer between system and surroundings.

·         Closed: Only energy can transfer.

·         Isolated: Neither energy nor matter can transfer.

·         Homogenous system: Consists of a single phase.

·         Heterogeneous system: Consist of two or more phases.

Isothermal: Constant T

Isobaric: Constant P

Isochoric: Constant V

Adiabatic: No heat transfer between the system and the surroundings.

Heat and work do not belong to system and are NOT properties of thermodynamics.

They are operations which performed on the system to alter its energy.

Properties

·         Extensive: Describe and depend on the size of the system. (Mass, volume, pressure…)

·         Intensive: Does not depend on the size of the system. (Molar volume, Molecular weight, Temperature…)

First law

Introduces the concept of internal energy.

·         DQ = U + W

From 1^st law;

When isothermal: DU= 0

                              DQ = DW

At constant volume: DW = 0

                                  DQ = DU

W = - PDV   it is a minus value for a closed system in expansion

W=nRTln.V_f / V_i   Can be taken for an isothermal expansion of a gas

Heat capacity

C=dQ/dT

At constant P: C_p= (dH/dT)_p

At constant V: C_v= (dU/dT)_v

To know how the reaction proceeds we need to know;

·         Enthalpy-H

·         Entropy-S

Enthalpy

DH^o  = å n H^o_products  - å n H^o_reactants

DH = U + PV

DH = C_pdT (as above mentioned in heat capacity)

DH = mCDǾ

Second Law

Describes entropy. Entropy is an idea of randomness in a reaction.

S>0 reaction is spontaneous

S<0 reaction is non spontaneous

S=0 reaction is at equilibrium

·         DS  =  DQ/T

At constant pressure

DS  =  DH/T

Also;

DS_universe  =  DS_system  +  DS_surroundings

DS^o  =  å n S^o_products  -  å n S^o_reactants

Third law

Absolute Entropy, S, =  0  at 0  Kelvins for a perfect crystal of a pure substance.

DG,  Gibbs Free Energy

The maximum amount of energy available to do useful work on the surroundings.

·         DG  = D H – T D S

DG  <  0  (-) Spontaneous

DG  >  0 (+) Spontaneous in the opposite direction       DG  =  0  equilibrium

·         DG^o  =   DH^o  -  T DS^o

DS (+), DH (-) Spontaneous at all temperature

DS (+), DH (+) Spontaneous at high temperatures (where exothermicity is relatively unimportant)     

    

DS (-), DH (-) Spontaneous at low temperatures

            (where exothermicity is dominant)

DS(-), DH (+)  Process not spontaneous at any temperature (reverse process is spontaneous at all temperatures)

·         DG  = DG^o  +  RT ln Q

                       Q  =  Reaction Quotient.

Free energy at equilibrium

·         G  =  0

·         So DG^o  =  -RT ln Q_equilibrium

              Q_equiliibrium  =  K_p (gases)

                                 =  K_c  (solution)

Characteristics of sp, sp2, sp3- hybrid orbitals

Characteristics of sp-hybrid orbital

·         Results from mixing of one s and one p-orbital.

·         Equivalent and symmetrical.

·         All orbitals have the same shape and energy.

·         Shape is oval shape which is in between spherical and pear shape.

·         Sp- hybrid orbitals are collinear. That means they are aligned in a straight line in opposite direction.

Characteristics of sp²-hybrid orbital

·         Results from mixing of one s-orbital and two p-orbitals.

·         They have the same shape and energy.

·         Lie in one plane.

·         Shape tends more towards the pear shape as the contribution of p-orbital is greater than the contribution of s orbital.

·         Spatial arrangement is trigonal. Angle between each pair is 120^o

Characteristics of sp³- hybrid orbital

·         Results from combination of one s-orbital and three p-orbitals.

·         Orbitals are equivalent and symmetrical.

·         Same shape and energy.

·         Arranged in tetrahedral angle where the angle between each pair is 109.5^o

·         Pear shaped but the lobes are much spread and somewhat shorter in length than the original p-orbitals.

Introduction to Nervous system

§ All animals are capable of corresponding to their surroundings. They gather stimuli from the environment by sensory receptors and the motor effectors react to it.

§  Most invertebrates and vertebrates process and integrate the information from the receptors and issue the instructions to the motor effectors. This process is done by the nervous system. It connects the receptors and effectors by the large network of nerve cells.

§  These nerve cells are called as “Neurons”.

§  The nervous system is principally consisting of Neurons and Glial cells.

Neurons

§  Consists of large cell body with cytoplasmic extensions.

§  Cell body is large containing the nucleus.

§  Other organelles such as mitochondria, ER, Golgi apparatus, microfilaments are present in the cell body.

§  Also Nissel bodies which are groups of ribosome are present in the cell body.

§  Two types of cytoplasmic extensions; Dendrites and Axon.

Dendrites	Axon
·         One or more can be extend from the cell body	·         Single Axon extends from the cell body
·         Can branch forming dentritic spines.	·         Branches only at the terminal end.
·         Schwann cells are not present. Myelin sheath is not present.	·         Schwann cells are present. Myelin sheath is present.
·         Radius tapers.	·         Constant radius
·         Short	·         Much longer
·         Transmit signals into the cell body.	·          Transmit signals away from the cell body.

§  Neurons communicate with other cells via synapses.Synaptic Bulbs at the Axon terminal ends are important to form these synapses.

Structure of Synapses

                               

Structural classes of neurons

  §  Bipolar neuron: One dendrite and one axon attached to the cell body.

  §  Pseudounipolar neuron: One extension from the cell body. That is an axon.

  §  Multipolar neuron: Many dendrites and one axon.

           

          

                   

Functional types of neurons

  §  Sensory neurons: Transmit massages from the receptors.

  §  Motor neurons: Transmit massages to the motor effectors.

  §  Intermediate neurons: Connect sensory and motor neurons.

Glial cells

  §  Non-neuronal, supporting cells.

  §  Support neurons both structurally and functionally.

  §  Large numbers of different types are present.

  §  Ex: Schwann cells

Mainly Nervous system can be divided in to two sections as Central Nervous System and Peripheral Nervous System. 

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