This Powerpoint Presentation is about Factors Affecting Reaction Rates solely for Educational Purposes.

1. CHEMICALREACTION
ANDFACTORSAFFECTINGREACTIONRATES

2. CHEMICAL REACTION
• Chemical reaction, a process in
which one or more substances, the
reactants, are converted to one or
more different substances, the
products. Substances are either
chemical elements or compounds. A
chemical reaction rearranges the
constituent atoms of the reactants
to create different substances as
products.

3. FACTORS AFFECTING REACTION RATES

4. Chemical reactions proceed at different rates.
The factors that affect reaction rates are:
Surface area of a solid reactant
Concentration or pressure of a reactant
Temperature
Nature of the reactants
Presence/absence of a catalyst

5. SURFACEAREA
Surface area is the exposed matter of a solid substance.
Imagine that you are holding a perfect cube of magnesium.
The surface area is the sum of the area of all six sides of the
cube. The surface area of the cube can be increased by
dividing the cube into smaller cubes. Surface area is
maximized when a single large cube is crushed to fine
powder.

6. SURFACE AREA
• In a reaction between magnesium metal and hydrochloric acid, magnesium atoms must
collide with the hydrogen ions. When the magnesium atoms form one big lump however, the
number of collisions per second between magnesium and hydrogen is higher, and the rate of
reaction is faster.

7. CONCENTRATION
The concentration of a substance can be expressed
in a variety of ways depending on the nature of a
substance. Aqueous solutions typically have their
concentrations expressed in mol/L. For example, a
solution made by dissolving sodium hydroxide in
water has its concentration expressed as moles of
NaOH per litre of solution. Gases can also have
their concentrations expressed in mol/L.

8. In terms of the collision theory, increasing the concentration of a reactant increases in the number
of collisions between the reacting species per second and therefore increases the reaction rate.
Consider the reaction between hydrochloric acid and zinc metal.
• In one beaker, 6.00 mol/L HCl is reacted with 2.00 g of Zn.
• In another, 1.00 mol/L HCl is reacted with 2.00 g of Zn.
Which reaction should occur at the faster rate?
In terms of the collision theory, collisions between zinc
atoms and hydrochloric acid are more frequent in the
beaker containing 6.0 M HCl - there is more acid per unit of volume.

9. CONCENTRATION
• You can change the concentration of an aqueous species by simply adding more
solute (to make it more concentrated) or adding more solvent (to make it more
dilute).

10. PRESSURE
•The concentration of a gas is a function of
the pressure on the gas. Increasing the
pressure of a gas is exactly the same as
increasing its concentration. If you have a
certain number of gas molecules, you can
increase the pressure by forcing them into
a smaller volume.

11. Under higher pressure or at a higher concentration, gas
molecules collide more frequently and react at a faster rate.
Conversely, increasing the volume of a gas decreases
pressure which in turn decreases the collision frequency and
thus reduces the reaction rate.

12. TEMPERATURE
• With the exception of some precipitation
reactions involving ionic compounds in
solution, just about all chemical reactions
take place at a faster rate at higher
temperatures. The question is why?
• Temperature (in Kelvin degrees) is
proportional to the kinetic energy of the
particles in a substance. For example, if the
Kelvin temperature of a substance is
doubled, then the average kinetic energy of
the particles in that substance is doubled.

13. • Recall that in any sample of matter (the example we used
previously was a gas), individual particles have different
kinetic energies. Some are moving fast some are moving
slowly, and most are moving at some intermediate speed.

14. NATURE OF THE REACTANTS
• Individual properties of substances also affect reaction rates. The scope of these
properties is broad and there are few generalizations that you can apply
consistently. Some of the properties in this category are state of matter,
molecular size, bond type and bond strength.
State of Matter:
Gases tend to react faster than solids or liquids.

15. Aqueous ions tend to react faster than species in other states of matter.
Bond Type
Reactions involving ionic species tend to proceed faster than reactions involving
molecular compounds.
Bond Strength
Reactions involving the breaking of weaker bonds proceed faster than reactions
involving the breaking of stronger bonds. For example, double carbon to carbon
bonds are stronger than single C-C bonds.

16. CATALYST
• A catalyst is a species that speeds up a chemical reaction
without being chemically changed upon completion of the
reaction. In other words, the mass of a catalyst is the same
before and after a reaction occurs.
Common examples of catalysts include:
• MnO2 in the decomposition of H2O2
• Fe in the manufacture of NH3
• Pt in the conversion of NO and CO to N2 and CO2

17. • Recall that collisions only result in reactions if the particles collide
with enough energy to get the reactions started (i.e. to overcome the
activation energy barrier).
• Also recall that activation energy corresponds to threshold energy.

18. REFERENCE:
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