Chemical Reactions
Rate of Reactions
Chemical Change .vs Physical Change
• Chemical Change –
occurs when a substance
changes composition by
forming a new substance
• Physical Change – a
change in the physical
form or properties of a
substance (no change in
composition)
Chemical Reactions
• Occur when substances
undergo chemical
changes to form new
substances
• Usually you will be able
to SEE changes
“Seeing” Chemical Reactions
• Production of
– Gas
– Heat
– Light
– Solid
• Change in color
• Bubbling
Chemical Reaction & Atoms
• Chemical reaction is a
rearrangement of atoms
• Reactants – what you
start with (they undergo
the chemical change)
• Products – what you end
up with (new substance)
Sulfuric Acid + Sugar  carbon + water (g)
Chemical Reactions & Energy
• In order for new
substances to be made,
bonds have to be broken
• Breaking bonds
requires ENERGY
– Heat, electricity, sound,
light, collisions
Forming Bonds & Energy
• Forming bonds
RELEASES Energy
– Heat, light, electrical
energy
Conservation of Energy
• The total energy before the reaction is equal
to the total energy of the products.
• Energy can be stored as chemical energy
– Stored within atoms and molecules
Kinds of Reactions
• Exothermic – more
energy is RELEASED
as products form
– Condenses or Freezes
• Endothermic – more
energy is NEEDED
(absorbed) to break
the bonds in the
reactants
– Evaporates or Melts
Reaction Rate
• The speed (rate) that a
reaction takes
Factors That Affect Reaction Rates
• Temperature
– hotter = increases rate
• Surface Area
– More = increases rate
• Concentration
– More = increases rate
• Pressure
– Higher = increases rate
• Size
– Smaller = increases rate
Catalysts – Enzymes
• Catalysts can be added to
make a reaction occur
faster
– They are not part of the
reactants or products
• Enzymes are natural
catalysts (proteins)
– Bind to a specific
substrate
Equilibrium
• When everything is
balanced!
• After a chemical
reaction we want to
have equilibrium!