chemical reaction rate

how fast does it go

How fast a chemical reaction occurs is called the reaction rate. Several factors affect the rate of a given chemical reaction. They include the: temperature of reactants. concentration of reactants. surface area of reactants. presence of a catalyst.

presence of a catalyst

Some reactions need extra help to occur quickly. They need another substance called a catalyst. A catalyst is a substance that increases the rate of a chemical reaction. A catalyst isnt a reactant, so it isnt changed or used up in the reaction. Therefore, it can catalyze many other reactions.

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 the Figure 1.3. 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.


concentration of reactants

Concentration is the number of particles of a substance in a given volume. When the concentration of reactants is higher, the reaction rate is faster. At higher concentrations, particles of reactants are crowded closer together, so they are more likely to collide and react. Did you ever see a sign like the one in the Figure 1.2? You might see it where someone is using a tank of pure oxygen for a breathing problem. Combustion, or burning, is a chemical reaction in which oxygen is a reactant. A greater concentration of oxygen in the air makes combustion more rapid if a fire starts burning. Q: It is dangerous to smoke or use open flames when oxygen is in use. Can you explain why? A: Because of the higher-than-normal concentration of oxygen, the flame of a match, lighter, or cigarette could spread quickly to other materials or even cause an explosion.


temperature of reactants

When the temperature of reactants is higher, the rate of the reaction is faster. At higher temperatures, particles of reactants have more energy, so they move faster. As a result, they are more likely to bump into one another and to collide with greater force. For example, food spoils because of chemical reactions, and these reactions occur faster at higher temperatures (see the bread on the left in the Figure 1.1). This is why we store foods in the refrigerator or freezer (like the bread on the right in the Figure 1.1). The lower temperature slows the rate of spoilage. Left image: Bread after 1 month on a warm countertop. Right image: Bread after 1 month in a cold refrigerator.


instructional diagrams

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factors that affect the rate of a chemical reaction include

a) concentration of reactants.

b) surface area of reactants.

c) temperature of reactants.

-->  d) all of the above

warmer reactants react more quickly than cooler reactants.

-->  a. true

b. false

food spoils faster at higher temperatures because heat is a catalyst.

a. true

-->  b. false

which statement is true about any catalyst?

a) it is a reactant in a chemical reaction.

b) it is used up in a chemical reaction.

-->  c) it can speed up many chemical reactions.

d) all of the above

warmer reactants have more energy and move faster.

-->  a. true

b. false

diagram questions

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