Question

chemical changes
read the text and use a highlighter to identify:

• the sentence that best defines a chemical change
• two examples of a chemical change
• the sentences that best explain the process that occurs during a chemical change

in a chemical change, one or more new substances are formed. for example, when you burn a match, the black substance left behind and the smoke released are new substances.
rusting is another example of a chemical change. the iron slowly combines with water and with oxygen in the air. this creates a new substance that was not there to begin with - rust!
during a chemical change, some of the chemical bonds between atoms are broken and new bonds are formed. this re - arrangement of atoms is what produces a new substance.
in the rust example, some of the bonds that hold iron atoms together are broken. the iron atoms form new bonds with oxygen and hydrogen atoms. this creates the new compounds that make up rust.
because breaking chemical bonds takes energy, many chemical changes cannot be easily reversed.

Explanation:

1. The sentence defining chemical change: "In a chemical change, one or more new substances are formed."
2. Two examples: Burning a match (black substance and smoke are new substances), rusting (iron combines with water and oxygen to form rust).
3. Explanation of the process: "During a chemical change, some of the chemical bonds between atoms are broken and new bonds are formed. This re - arrangement of atoms is what produces a new substance."

Answer:

• Sentence defining chemical change: In a chemical change, one or more new substances are formed.
• Two examples: Burning a match; Rusting
• Sentences explaining the process: During a chemical change, some of the chemical bonds between atoms are broken and new bonds are formed. This re - arrangement of atoms is what produces a new substance.