Summary Energy change and rate of reactions

-
Definition

-



Symbol
Bond and bond
length
energy
Heat of reaction (At--The chemical potential the system
net
change of energy of




Exothermic reactions Reactions which chemical
transform potential into thermal
--

energy energy



Endothermic reactions >
-
Reactions which transform thermal energy into chemical potential energy



Activation energy (Ea)
--
The minimum
energy required to start a chemical reaction

or

The
required to form the activated complex
energy


Activated complex --
A
high energy ,
unstable , temporary transition state between the reactants and


the
products s.

Endothermic reactions break down bonds Exothermic reactions build bonds
AH >0
1HL0

-
A
stronger bond requires more
energy
to build/break down bonds
-


Exothermic reactions release and thus increases the temperature of the
energy
reaction mixtures
Endothermic reactions absorb thus decrease the temperature of the
-



and
energy
reaction mixtures .




Energy profile graphs :
Exothermic reactions : Endothermic reactions :

Activated
E Activata E
complex
-

o
t -
u -
1

Ea

..........
Produce ---Eq
-


E
-
AH
Products Reactants ---
↳
V - - -
- - -




Course of reaction Course of reaction

,kates
of reactions :




Rates reaction The
of - >
change in concentration per unit time of either a reactant or
product.


Asproducts) - Adreactants

Rate of reaction = At
=
At




-



On concentration the
a time
graph the
gradient represents rate of reaction .




Collision
theory :



Collision different before reaction
theory
- >
The particles of reactants first have to collide with each other a can take place.




-




Only effective collisions can lead to chemical reactions




> A collision is effective when:

1 Particles have break bonds and activation
enough kinetic energy to existing energy
.



overcome


2
. Particles have the correct orientation




Factors that influence the rate of reaction



Nature of reactants :

Ionic react faster than covalent
substances usually substances
-




Organic due covalent molecules
-




molecules take to bonds and
large
longer many
Metals
high
-




in the reactivity series react faster
up



Concentration : 10 mol dm-3
.




-
5 mol . dm-3
Only mol dm-3
-



in
aqueous /age
solutions and gasses/y) 0
,5 .




-




Number particles container
-
The reaction limited
of
per volume in the increases is
by
another substance
More collisions
-




If substance was
limiting reagent
-


occur
per second
then volume of CO2 produced would be

Increases Time
-




the chance of effective collisions per second to occur . greater with a
greater concentration
-
Rate of reaction increases