Chemical Reactions Quiz

Grade 7 · Science · Quiz

Test your knowledge of reactants, products, chemical equations, and signs of chemical change.

Questions

In a chemical reaction, the starting substances are called:
1. Products
2. Reactants
3. Elements
4. Compounds
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Answer: Reactants
Reactants are the substances that enter into and are altered in the course of a chemical reaction. Products are what is formed.
Which of the following is a sign that a chemical reaction has occurred?
1. Water changing from liquid to ice
2. A color change in a substance
3. A rock being broken in half
4. Salt dissolving in water
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Answer: A color change in a substance
A color change is a common sign that a new substance has been formed, indicating a chemical reaction. The other options are physical changes.
In a chemical reaction, atoms are created and destroyed.
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Answer: False
Atoms are never created or destroyed in a chemical reaction — they are only rearranged. This is the law of conservation of matter.
What does the law of conservation of mass state?
1. Energy is always created in reactions
2. Mass is lost during burning
3. The mass of reactants equals the mass of products
4. Atoms change identity in a reaction
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Answer: The mass of reactants equals the mass of products
The law of conservation of mass states that mass is neither created nor destroyed. The total mass of reactants equals the total mass of products.
The substances formed at the end of a chemical reaction are called ___.
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Answer: products
Products are the new substances formed as a result of a chemical reaction. Reactants go in; products come out.
What type of reaction occurs when two or more substances combine to form one new substance?
1. Decomposition
2. Combustion
3. Synthesis
4. Single replacement
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Answer: Synthesis
A synthesis (combination) reaction joins two or more reactants to form one larger product. Example: 2H₂ + O₂ → 2H₂O.
Which of the following is an example of combustion?
1. Baking soda dissolving in water
2. Wood burning in a fireplace
3. Salt and pepper mixing
4. Ice melting on a sidewalk
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Answer: Wood burning in a fireplace
Combustion is a chemical reaction between a fuel and oxygen that produces heat and light. Burning wood is a classic example.
A physical change and a chemical change produce the same type of new substance.
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Answer: False
A physical change (like melting) does not create a new substance. A chemical change creates an entirely new substance with different properties.

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