Rates of Reactions

Chapter 13, Section 4

Rates of Reactions

A reaction takes place only if the particles of reactants collide.

The speed at which new particles form is called the rate of reaction.

Activation EnergyA chemical reaction needs a boost of energy

before the reaction can start. Activation Energy—smallest amount of

energy that molecules need to reactEx: friction, electric

spark, light

Sources of Activation Energy…There are 4 factors that affect the rate of a reaction. 1. Temperature—higher temp=faster reaction

2. Concentration—higher conc.=faster reaction 3. Surface Area—increase S.A.=faster reaction

4. Presence of an inhibitor or catalyst

Inhibitor—slows down or stops a reactionEx: preservatives added to foods to slow down

growth of bacteria

Catalyst—speeds up a reactionEx: enzymes

Which is quicker?Step 1: Put 250mL of water into a beaker and place it on

the hot plate.Step 2: Put 250mL of water into a second beaker and set

it to the side.Step 3: Wait for your water on the hot plate to warm up.Step 4: Remove your beaker from the hot plate and turn it

off.Step 5: Place an effervescent tablet in each one of the

beakers at the same time. Time each reaction.Step 6: On your paper, record your observations for each

reaction.

Answer the following…

1. In which beaker did the reaction occur at a faster rate?

2. Why does grinding a solid into a powder increase reaction rate?

3. Explain how chewing your food thoroughly can help your body digest food.