Rates of Reaction

1
Rates of Reaction

• A chemical reaction involves a collision between
  particles.
• The particles collide and make new substances
• The particles which react are called the
  reactants
• The substances which are made are called the
  products

2
How do we make the reaction go faster?

• There are four things that we can change to make
  the reaction go faster.
• They are
• Temperature
• Surface area
• Concentration
• Using a catalyst

3
Temperature

• When we increase the temperature we give the
  particles energy
• This makes them move faster
• This means they collide with other particles more
  often
• So the reaction goes faster.

4
Surface area

• If we make the pieces of the reactants smaller we
  increase the number of particles on the surface
  which can react.
• This makes the reaction faster.

The particles on the surface can react
When cut into smaller pieces the particles on the
inside can react
5
Concentration

• If we make one reactant more concentrated (like
  making a drink of orange squash more
  concentrated)
• There are more particles in the same volume to
  react
• So the reaction goes faster.

There are less red particles in the same volume
so there is less chance of a collision
There are more red particles in the same volume
so there is more chance of a collision so the
reaction goes faster
6
Using a catalyst

• A catalyst is a chemical which is added to a
  reaction.
• It makes the reaction go faster.
• The catalyst does not get used up in the
  reaction.
• It gives the reaction the energy to get started

7

• Fill in all the gaps
• 1. A chemical reaction involves a ______between
  particles.
• 2. The_____collide and make new substances.
• 3. The particles which react are called the
• 4.The substances which are made are called the
• 5.There are _____things that we can change to
  make the reaction go____.
• 6.They are________, ________, _________ and
  _________.

8
EXOTHERMIC AND ENDOTHERMIC REACTIONS

• Exothermic- heat energy EXITS the system
• ex. Combustion, evaporation of water
• - surroundings usually feel warmer
• An example of an exothermic reaction is the
  mixture of sodium metal and chlorine gas which
  yields table salt.
• 2Na(s) Cl2(g) ---gt2NaCl(s) energy

9
Endothermic

• - heat energy ENTERS the system
• - ex. Cold packs, melting ice
• - surroundings usually feel cooler
• How do cold packs work?
• -The outer pouch contains water. The inner pouch
  contains ammonium-nitrate. When you pop the
  inner pouch, the chemical reaction absorbs heat
  energy from the surroundings. This is an
  endothermic reaction.
• The temperature of the solution falls to about 35
  F for 10 to 15 minutes.

10
Activation energy

• The minimum energy that reactant molecules must
  possess in order for the reaction to start.
• In exothermic reactions, products have less
  energy than reactants.
• In endothermic reactions, products have more
  energy than reactants.

11
PRACTICE

• Give three examples of exothermic reactions in
  everyday life.
• Classify each reaction as exo- or endo thermic
• a.Photosynthesis
• b.Melting ice
• c.Sodium hydroxide dissolving in water and the
  temperature of the solution rising.
• d.Ammonium chloride dissolving and the
  temperature falling.