CHEMICAL REACTIONS

CHEMICAL REACTIONS

Chemical reaction 

     -occurs when new bonds form 
                            or
old bonds break between atoms.

     - are the foundation of all life processes.

     -  interactions of valence electrons are the basis of all chemical reactions.

REACTANTS

the starting substances of a chemical reaction.

eg. 

        2H2 +O2 - 2H2O

Reactants- 2H2 and O2

PRODUCTS

The ending substances of a chemical reaction.

eg.

       2H2 +O2 - 2H2O

Products-  2H2O


In a chemical reaction

         total mass of reactants = total mass of products.

Therefore the number of atoms of each element is the same before and after the reaction.

Because the atoms are re-arranged, the reactants and products have different chemical properties.

METABOLISM

All the chemical reactions occuring in the body.

FORMS OF ENERGY

ENERGY-

             en= in
             -ergy= work


Capacity to do work.

TWO PRINCIPAL FORMS OF ENERGY

1. POTENTIAL ENERGY

2. KINETIC ENERGY

POTENTIAL ENERGY

Energy stored by matter due to position.

eg. the energy stored in water  behnd a dam.

KINETIC ENERGY

Energy associated with matter in motion.

eg.  when the gates of the dam opened, potential energy of water  is converted into kinetic energy.


CHEMICAL ENERGY

Form of potential energy stored in the bonds of compounds and molecules.


LAW OF CONSERVATION OF ENERGY


The total amount of energy present at the beginning and end of a chemical reaction is the same.

Although energy can be neither created nor destroyed, it may be converted from 1 form to another.

Conversion of energy from 1 form to another generally releases heat , some of which is used to maintain normal body temperature.


ENERGY TRANSFER IN CHEMICAL REACTIONS.

EXERGONIC REACTIONS

Ex = out

Reactions that release energy than they absorb.

ENDERGONIC REACTION

End= within

Absorbs more energy than they release.

Energy released from an exergonic reaction often is used to drive an endergonic reaction.


IN BODY


Exergonic reaction occur as nutrients such as glucose are broken down

       some of the energy released may be traped in the covalent bond of ATP.

eg.

When 1 molecule of glucose is completely broken down, 
    
       chemical energy in its bonds can be used to produce as many as 38 molecules of ATP.

1. The energy transferred to the ATP molecules are then used to drive endergonic reactions needed to build body structures such as muscles and bones.



2. The energy in ATP is also used to do the mechanical work involved  in muscle contraction or movement of substances into and out of cells.


ACTIVATION ENERGY OF THE REACTION

       The collision energy needed to break the chemical bonds of the reactants.

  - is needed to start a reaction.

    - as new bonds are formed , energy is released into surroundings.



INFLUENCE OF TEMPERATURE AND CONCENTRATION OF PARTICLES IN A CHEMICAL REACTION

1. TEMPERATURE

As temperature rises

              particles of matter move about rapidly.

Higher the temperature of matter

             -the more forcefully particles will collide
             - greater the chance that a collision will produce a reaction.

2. CONCENTRATION

When more particles are added to a given space 
                           OR
When pressure on the space increases

                      -the concentration of particles increases

                      - forces the particles to come closer together

                      - they collide more often.


CATALYSTS

Chemical compounds 
    that speed up the reactions

             by lowering the activation energy needed for a reaction to occur.

The most important catalyst in our body
                                                       -ENZYMES

1. Catalyst does not alter the difference in potential energy between reactants and products

      it lowers amount of energy needed to start the reaction

2. Catalyst helps to properly orient the colliding particles.
       thus they interact at the spots that make the reaction happen.

3. Catalyst itself is unchanged at the end of the reaction.


TYPES OF CHEMICAL REACTIONS

1. SYNTHESIS REACTIONS-  ANABOLISM

2. DECOMPOSITION REACTIONS- CATABOLISM

3. EXCHANGE REACTIONS

4. REVERSIBLE REACTIONS


1. SYNTHESIS REACTIONS

SYNTHESIS= TO PUT TOGETHER

When 2 or more atoms, ions or molecules combine to form new and larger molecules.

eg. 

     A +B - AB
  
     N2 + 3H2 - 2NH3

     2H2 + O2 - 2H2O


ANABOLISM

All the synthesis reactions that occur in our body 

are usually endergonic because they absorb more energy than they release.

eg.  Amino acids combine to form proteins.


2. DECOMPOSITION REACTION

Split up large molecules into smaller atoms, ions or molecules.

AB - A+ B

CATABOLISM

The decomposition reactions that occur in our body.

are usually exergonic because they release more energy than they absorb.

eg.  Series of reactions that break down glucose to pyruvic acid with the net production of 2 molecules of ATP.


3. EXCHANGE REACTIONS

consists of both synthesis and decomposition reaction.

eg.

  AB + CD - AD + BC

   HCl + NaHCO3 -  H2CO3 + NaCl


4. REVERSIBLE REACTIONS

The products can revert ton the original reactants

Is indicated by 2 half arrows pointing in opposite directions.

AB   ⇄  A + B

Some reactions are reversible only under special conditions

          H2O
AB     ⇄   A + B
        HEAT

AB breaks down into A and B only when H2O is added.

A and B react to produce only when heat is applied.