Lesson 5

How Fast a Reaction Takes Place

Competency 5: Define catalyst and describe how it affects reaction rate.

Chemical reactions and catalystsA chemical reaction involves a chemical change, which happens when two or more particles (which can be molecules, atoms or ions) interact. For example, when iron and oxygen react, they change to a new substance, iron oxide (rust). Iron oxide has different chemical properties to iron and oxygen. This is different to a physical change. For example, water can turn to ice, but ice is still water in another physical state – ice and water have the same chemical properties.

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