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Chemical Reactions: Practice Questions with Answers

Curriculum: Chemical ReactionsGrades: 8–10Questions: 12Mode: Practice

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1. What is produced when substances undergo a chemical reaction?

  1. The exact same substances, just rearranged in appearance
  2. New substances with different properties
  3. Nothing new; the mass simply disappears
  4. A physical mixture that can be separated by filtering
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Answer: B. New substances with different properties
A chemical reaction rearranges atoms into new substances that have different chemical and physical properties from the starting materials.

2. Which of the following is a sign that a chemical reaction has occurred?

  1. A solid is ground into a fine powder
  2. Water freezes into ice
  3. A gas forms with bubbling, or a color change occurs
  4. The object changes shape but stays the same substance
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Answer: C. A gas forms with bubbling, or a color change occurs
Bubbling (gas production) and unexpected color changes are classic signs that new substances have formed, indicating a chemical reaction took place.

3. In a chemical equation, what are the substances on the left side called?

  1. Products
  2. Solvents
  3. Reactants
  4. Catalysts
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Answer: C. Reactants
Reactants are the starting substances that are written on the left side of a chemical equation before the arrow.

4. In a chemical equation, what are the substances on the right side called?

  1. Products
  2. Indicators
  3. Isotopes
  4. Reactants
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Answer: A. Products
Products are the new substances formed by a chemical reaction, and they are written after the arrow in a chemical equation.

5. What law states that mass is neither created nor destroyed in a chemical reaction?

  1. The Law of Conservation of Mass
  2. The Law of Definite Proportions
  3. The Law of Motion
  4. The Law of Gravity
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Answer: A. The Law of Conservation of Mass
The Law of Conservation of Mass states that in a chemical reaction, the total mass of the reactants equals the total mass of the products, since atoms are only rearranged, not created or destroyed.

6. What is a chemical reaction that releases heat called?

  1. Exothermic
  2. Endothermic
  3. Isothermic
  4. Neutral
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Answer: A. Exothermic
An exothermic reaction releases energy, usually as heat, so the surroundings often feel warmer during the reaction.

7. What is a chemical reaction that absorbs heat called?

  1. Combustion
  2. Exothermic
  3. Synthesis only
  4. Endothermic
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Answer: D. Endothermic
An endothermic reaction absorbs energy from its surroundings, which is why the surrounding area often feels cooler during the reaction.

8. Which symbol in a chemical equation means "yields" or "produces"?

  1. The plus sign (+)
  2. The equals sign (=)
  3. The parentheses ( )
  4. The arrow (->)
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Answer: D. The arrow (->)
The arrow in a chemical equation points from reactants to products and is read as "yields" or "produces."

9. What do we call a substance that speeds up a reaction without being used up?

  1. A reactant
  2. A catalyst
  3. A product
  4. A solute
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Answer: B. A catalyst
A catalyst speeds up the rate of a chemical reaction but is not consumed or permanently changed by the reaction, so it can be used again.

10. Which of these is an example of a physical change, not a chemical change?

  1. Milk souring and smelling bad
  2. Melting an ice cube into liquid water
  3. Bread turning moldy over time
  4. A firework exploding with colored light
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Answer: B. Melting an ice cube into liquid water
Melting ice only changes water from a solid to a liquid state; no new substance is formed, so it is a physical change, not a chemical one.

11. What does the coefficient in front of a chemical formula tell you?

  1. The number of molecules (or moles) of that substance
  2. The temperature of the reaction
  3. The charge of the atom
  4. The state of matter of the substance
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Answer: A. The number of molecules (or moles) of that substance
A coefficient placed in front of a chemical formula shows how many molecules or moles of that substance are involved in the reaction.

12. Which of the following best describes "reactants"?

  1. The energy released during a reaction
  2. The leftover waste after a reaction finishes
  3. The tools used to measure a reaction
  4. The starting substances that combine or change during a reaction
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Answer: D. The starting substances that combine or change during a reaction
Reactants are the original substances that enter into a chemical reaction and are transformed into products.
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