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

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

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.

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

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

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

Fill in all the gaps1. A chemical reaction involves a ______between particles.2. The_____collide and make new substances.3. The particles which react are called the4.The substances which are made are called the5.There are _____things that we can change to make the reaction go____.6.They are________, ________, _________ and _________.

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) --->2NaCl(s) + energy

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.

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.

PRACTICE• Give three examples of exothermic reactions

in everyday life.• Classify each reaction as exo- or endo

thermic:a.Photosynthesisb.Melting icec.Sodium hydroxide dissolving in water and

the temperature of the solution rising.d.Ammonium chloride dissolving and the

temperature falling.