1) Chemical reactions can be endothermic or exothermic depending on whether heat energy is absorbed or released during the reaction. 2) The organization and disorder of particles changes as matter changes form - gases have more disorder than solids or liquids. 3) Balanced chemical equations follow the law of conservation of matter, with the same number and type of atoms on both sides of the equation.

1. S e c t i o n o n e & t w o
B y :
Y o u s s e f B e r b a r

2. Total amount of energy in universe stays the same
 When matter undergoes the change , there is often
change of energy
 In A heat energy goes in and chemicals gain energy
 In B hear energy is released and the chemicals lose
energy .

3.  When you add heat energy to something, the particles
inside it gain the energy , so it move faster .
 The extra energy could also change the bonds that
exist between atoms or molecules.
 Bonds holding a molecule together : hold the
atoms in an individual molecule together .
 Attractive forces (between molecules ) : hold the
molecules of solids and liquids together and prevent
them from separating to form a gas .
 chemical bonds are much stronger than the
intermolecular forces of attraction so it takes a lot
more energy to break bonds in any chemical reaction

4. Perspective of the energy change
 Endothermic : A process when the matter absorbs
heat energy.
 Exothermic : A process when the matter releases
heat energy.

5. Organization of particles
 When a substance changes the origination of its
molecules also changes .
 Chemists choose to measure, or speak in
disorganization.

6.  From 1 to 2 the (disorder) or(spread) of particles
of substance increases .
 Chemists quantify “spread” or disorder under the
name entropy
 Entropy (S): The disorder of particles in a
substance.
 Gases have their molecules very spread out ,
because reactions that create gases from solids
and liquids have an increase in disorder
 CaCO3(s) + energy →CaO(s) + CO2(g)
That means One mole of calcium carbonate will
produce one mole of calcium oxide and one mole
of carbon dioxide when it goes to completion.
With the entropy values, it can be seen
mathematically that the total entropy increases.

7. Balanced chemical equation
 Balanced chemical equations are an example of
the Law of Conservation of Matter.
 Law of Conservation of Matter : the amount of
matter present before and after a chemical change
remains the same. Or matter cannot be created
or destroyed, but it can be changed from form to
another .
 When chemical equations are written, the
quantity of an element on the reactant side must
equal the quantity of that element on the product
side

8. How to balance an equation
 For example : Balance the equation for the reaction of
iron(III) oxide with hydrogen to form iron and water.
 First : write the equation without balancing
Fe2O3+H2→Fe +H2O

10.  Note : you can’t change the formula of the product
so Use coefficients to balance an equation. Never
change subscripts.
 For example : when you write equation of water you
may start by : H2+O2→H2O then add the
coefficients it will be
2H2+O2→2H2O .
To balance this equation, some people may want to
change the formula of the product to H2O2 so it will
give hydrogen peroxide not water.
H2+O2→H2O2

16. Thanks for listening
Yousef Berbar