http://www.ck12.org Chapter 3. Chemical Interactions
Surface Area of Reactants
When a solid substance is involved in a chemical reaction, only the matter at the surface of the solid is exposed to
other reactants. If a solid has more surface area, more of it is exposed and able to react. Therefore, increasing the
surface area of solid reactants increases the reaction rate. Look at the hammer and nails pictured in theFigure3.42.
Both are made of iron and will rust when the iron combines with oxygen in the air. However, the nails have a greater
surface area, so they will rust faster.
FIGURE 3.42
Presence of a Catalyst
Some reactions need extra help to occur quickly. They need another substance called a catalyst. Acatalystis a
substance that increases the rate of a chemical reaction. A catalyst isn’t a reactant, so it isn’t changed or used up in
the reaction. Therefore, it can catalyze many other reactions.
Summary
- How fast a chemical reaction occurs is called the reaction rate.
- Several factors affect the rate of a chemical reaction, including the temperature, concentration, and surface
area of reactants, and the presence of a catalyst.
Vocabulary
- catalyst: Substance that increases the rate of a chemical reaction but is not changed or used up in the reaction.
- reaction rate: Speed at which a chemical reaction occurs.
Explore More
Watch the video about reaction rate at the following URL, and then answer the questions below.
http://www.youtube.com/watch?v=F-Cu_AoWOK4
- What is collision theory?
- How does collision theory relate to factors that affect reaction rate?
Review
- Define reaction rate.
- List factors that influence the rate of a chemical reaction.