. BIOENERGITICS

Terms:

Energy : the ability to perform work , and it's divided into

two categories :

1) Kinetic energy : energy produces by moving object .

2) Potential energy : energy available by variation of an

object position , and it's able to perform if the situation is

able to perform .

Examples :

- when athletic is standing , he has a potential energy ,and

when he is running , he has a kinetic energy .

- the energy stored in the food is potential .however, it can

transform through a series of RXNs into kinetic energy .

- when you make a stress on the spring , it stores a potential

energy and when you release it ,the energy becomes kinetic.

Questions :

* why do RXNs occur ?

answer :

the reactants react to become more stable , which means :

to reach less potential energy , because the amount of

potential energy determines if the RXN will occur or not .

* why are products more stable than reactants ?

answer :

because it has less potential energy than reactant to

perform into another form .

Bond dissociation energy ( BDE ):

the energy required to dissociate bonds between atoms in

the material or compound or …etc .

it depends on many factors , such as :

bond type .-

number of bonds .-

N2 : triple covalent bond. Higher BDE.

Cl2 : single covalent bond. Less BDE.

Role :

the higher the # of bonds , the larger the amount of

produced energy of dissociation .

THERMODYNAMIC :

Terms :

Thermodynamic : the science studies the transformation -

of heat + other kinds of energy in any system or pathway .

: used to express how many potential energy

exists in the system .

Kinetic : studies the RXN in the dynamic (motion) state .-

- Bioenergic : studying of thermodynamic inside biological

system .

THERMODYNAMICS LAWS :

1) First law :

the energy converts from one form to another , but can't be

created or destroyed .

The total energy in the universe is assumed constant .

- This law is important in biochemical pathways. How ?

if we need a certain amount of energy to convert

reactants>>>products , then we will get the same amount of

energy of we convert products>>>reactants .

- This is important to determine the bidirectionality of

pathways if the RXN is reversible .

2) Second law :

every transformation of energy in the universe are

inefficient , and there is no system works with 100%

capacity. Thus there is loss of energy from the specific

pathway .however, there is no loss of energy from the

universe.

so , where this lost energy escape ?

Generally , there are two ways :

1) HEAT :

-part of the internal energy is used to perform

work.however, the extra energy lost as heat .

2) In spontaneous RXNs :

all spontaneous RXNs in the universe increase in disorder .so

we need energy to perform work , so as to make it organized

(in order) .

Entropy ( S) : disorder .

: Summary

ENERGY :

1) USED : consumed as work .

2) LOST : as heat .

: in spontaneous RXNs to make it ordered .

ENTHALPY :

definition : express how much heat exists in the system .

measured as how much energy involved in bonds .

Terms :

Exothermic : RXNs produces heat .

Endothermic : RXNs absorbs heat .

- exothermic RXNs are spontaneous RXNs , and endothermic

RXNs are non-spontaneous RXNs . BUT not always ! WHY ?

well , if the RXN starts and proceed to the end , I can judge

that it's spontaneous .

in other words , if there is one factor , I can judge the

spontaneity of RXN based on this factor .

- if there are more than one factor that determines the

spontaneity , then taking the impact of one factor can't

determine the spontaneity of the RXN .

- if we say that Exothermic RXN is always spontaneous , that

means : the only determinant of the spontaneity in this RXN

is the heat . BUT that isn't true , based to this eq :

∆G = ∆H – T ∆S .

I mean : there are factors other than the heat , for example :

the Entropy .

Example :

when the snow is melting , it takes heat from the

surrounding , so the weather becomes cold .however : this

RXN is endothermic and it's also spontaneous . HOW ?

Because there are two factors that determine the

spontaneity of this RXN : the heat + the Entropy , which is

the degree of disorder .

when the material converts from solid>>liquid>>gas ,

the Entropy increases .

Free energy change :

it’s the total potential energy that spread with respect to the

temperature .

∆G = ∆H – T ∆S .

So the HEAT and the ENTRPOY determines the spontaneity .

Endergonic : RXNs need energy . it’s spontaneous always .

Exergonic : RXNs give energy . it’s non- spontaneous always.

Always !! WHY ??

Because they are terms of energy , BUT :

Exothermic and Endothermic are terms of heat ( ∆H ).

Values of ∆G :

- determines if the RXN is spontaneous or not .

it could be :-

(+) : Endergonic.

(--) : Exergonic.

At equilibrium :

As a whole system :

it doesn’t gain or give energy .

( neither Endergonic nor Exergonic )

As steps inside the system :

some steps are Endergonic.

some steps are Exergonic.

Activation Energy :

- the energy which is needed to reach the Transition State .

- Transition State:

the most unstable form of reactants that has the highest

energy .

the total free energy difference in any system at any : G∆

condition .

- determines the spontaneity of the RXN .

: the total free energy difference in any system at °G∆

specific condition / standard conditions ( 25°c + 1 atm.)

the total free energy difference in any system at : G°'∆

specific conditions ( 25°c + 1 atm. + pH = 7 ) .

NOTES :

1) ∆G° , ∆G°' : used in experiments . To study the impact of

one factor , we should fix the other factors .

2) ∆G : determined by the initial step and the final step ONLY

In maths words :

- if we calculate the total difference of energy in a RXN

involved many steps , we have to calculate the energy

difference between reactants and products in each step .

so we will eliminate the similar factors and at the end :

the net eq :

∆G = final products energy – initial products energy.

in my opinion , the mathematical explaination isn't

important .

please listen to the record if you want to understand it well .

the minute : (25:50).

3) differentiate between :

Thermodynamic : deals with the properties of the material.

(the total potential energy) . so it will not be affected by the

mechanism .

Kinetic : deals with movement meanings , like :

mechanism , pathways , steps , rate of RXN …etc .

4) ∆G : isn't affected by the mechanism of RXN . we are

interested in the difference in energy between reactants and

products regardless the pathways or the mechanism .

we just want to know if the RXN will give energy or absorbs

it at the end of RXN .

:TY OF RXN FAVORABILI

a term of thermodynamic , that doesn't affected by

the rate of RXN .

SO if the RXN is favorable , that doesn't mean it's fast or

slow.

:THEORY OF COLLISION

the reactants are colloid to perform products .

Successful collision :

1) existing of collision between reactants .

2) the collision should be at a certain speed .

* Are all favorable RXNs occur at rooms temp. ?

there is a collision at the room temp. .however , it's not

active . because it doesn't colloid at the required speed to

make the collision successful .

FACTORS AFFECT ∆G :

1) WHEN THE TEMP. INCREASES :

- the frequency of the collisions increases .

- the speed of the collisions increases .

2) WHEN THE CONCENTRATION OF ANY REACTANT

INCREASES:

- the chances of collision increases .

3) THE EFFECT OF CATALYSTS :

Catalysts affect the rate of RXN , but not affect the ∆G ,

since ∆G is constant for a certain RXN .

: REVERSIBLE RXNs

it can go in both directions : reactant >>product and

vice versa.

: CHEMICAL EQUILIBRIUM

a term of rate that means :

the rate of converting products>>reactants =

the rate of converting reactants>>products regardless the

concentration of products and reactants .

Example :

if there are two rooms : a, b .

room a contains 45 student,and room b contains 70

students. Every 5 minutes there are 2 students come from

a>>b , and 2 students come from b>>a. then a , b is at

equilibrium though they contain different # of students.

: EQUILIBRIUM CONSTANT

- the equation exists in the slides .

- IF :

1) Keq < 0.001 : essentially but not exactly there is no RXN ,

Because : A,B increases and M,N decreases .

So there is no RXN .

2) 0,001< Keq < 1 : more reactants than products.

3) 1< Keq < 1000 : more products than reactants.

4) Keq >>1000 : RXN is gone to completion .

STRESS :

- anything that affect in the equilibrium .

1) effect of CONCENTRATION :

- If we increase the amount of reactants , the RXN will shift

itself to make more products , and vice versa .

- this effect is important in our body in many pathways .

there is a trick :

* let's talk about a system in equilibrium in the body .

however , we change the concentration of reactants or

products :

if we taking the products out , then the RXN Will go forward

direction to make products .

so we had broken the equilibrium down .

* In feedback regulation :

pathways inhibition occurs . for example :

* Glucose converts to Glucose – 6 phosphate when it leaves

the cell . however , the last one can't leave the cell .

so the equilibrium is shifting all the time toward getting

Glucose inside the cell .

2) effect of TEMP. :

TEMP. : a term of heat . according to heat there are :

* Exothermic RXN : gives heat as product .

If we applying temp. , we will give the system a heat . so we

are shifting the equilibrium in the backward direction , and

we are not favoring the RXN .

* Endothermic RXN : absorbs heat .

If we applying temp. , we will give the system a heat . so we

are shifting the equilibrium in the forward direction , and we

are favoring the RXN .

3) effect of CATALYSTS :

Generally , they accelerate the forward and the backward

direction in the same manner .

قال ابن قيم الجوزية رحمه اهلل تعالى: ال يلمه إال اإلقبال على اهلل ، ) في القلب شعث

وفيه وحشة ال يزيلها إال األنس به في خلوته ، وفيه حزن ال يذهبه إال السرور بمعرفته وصدق معاملته ، وفيه قلق ال يسكنه إال االجتماع عليه والفرار منه إليه ،

إال الرضا بأمره ونهيه وقضائه ، يطفئها وفيه نيران حسرات ال لى ذلك إلى وقت لقائه ،ومعانقة الصبر ع

وفيه طلب شديد ال يقف دون أن يكون هو وحده مطلوبه ، وصدق ، ودوام ذكره ، واإلنابة إليه، وفيه فاقة ال يسدها إال محبته

ولو أعطي الدنيا وما فيها لم تسد تلك الفاقة منه أبدا ( .اإلخالص له .(2/333مدارج السالكين ) هلل الذي بنعمته تتم الصالحات .الحمد

لطفي صوان .