Chemical changes occur when substances combine to form new substances and are not reversible without further chemical reactions. The rate of a chemical reaction depends on factors like the nature of reactants, temperature, concentration, surface area, and presence of catalysts. A catalyst lowers the activation energy needed for molecules to collide and react, accelerating the reaction rate without being consumed in the process.

2. Chemical Change
 Occur when a substance
combines with another to
form a new substance.
 Not reversible except by
further chemical reaction.

3. Reaction Rate
- is the speed at which reactants are
converted into products and the rate which
chemical reaction proceeds.

4. Collision Theory
 Is based on the assumption that for a
reaction to occur it is necessary for the
reacting species (atoms or molecules) to
come together or collide with one another.

5. Activation energy, 𝐸𝑎
Serves as an energy barrier that
reactant molecules must overcome to
be converted to the products.
The lower the energy barrier, the
easier it is to form the products.

7. Legend:
Energy of Reactants = 𝐸𝑅
Activation energy = 𝐸𝑎
Energy Activated Complex = 𝐸𝐴𝐶
Energy of the products = 𝐸𝑃

8. Factors
Affecting
Reaction
Rate
Nature of
Reactants
Temperature
Presence
of Catalyst
Surface
Area
Concentration
of Reactants

9. Nature of Reactants
 Individual properties also affect
reaction rates.
Reactants in Liquid and Gas phase
reacts faster than the reactants of
Solid.

11. Effect of Temperature
 According to Kinetic Molecular Theory “as the
temperature increases, the average kinetic
energy of molecules also increases.
 It also increases the frequency of collisions.
 If the temperature of the reacting system is
increased, the reaction also increases.

13. Effect of Concentration of Reactants
If the concentration of the reactant is
increased the reactant particles
become more crowded.

15. Surface Area
 Is the exposed matter of a solid substance.
The rate of reaction of a solid substances is
related to its surface area.
 Smaller reactant particles provide a greater
surface area which increase the chance for
collision.
 The higher the surface area, the faster the
reaction rate.

17. Presence of Catalyst
 A Catalyst is a substance that increase the
rate of reaction without being used up or
permanently changed.
 It lowers the activation energy.