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Section 2.4 – Chemical Reactions Review Questions

1. How does a chemical change affect thecomposition of matter?
- During a chemical change, the composition of matter always changes.

2. Name four possible clues that a chemical change has taken place.
- Transfer of energy,change in color, the production of gas (bubbles), the formation of precipitate


3. Classify the following as physical or chemical changes.
a. Water boils on the stove
b.Milk is left out and turns sour
c. Rubbing alcohol evaporates quickly from the surface of a table.
d. A French chef making a sauce with brandy is able to heat it to remove thealcohol from the brandy, leaving just the brandy flavoring.

e. Hydrogen peroxide fizzes when applied to a wound.
f. The tire on my bike popped when I added too much air to it.g. Salt dissolves in water
h. A piece of rubber stretches when you pull on it.
i. A copper pan forms a blue-green coating when it is used a lot.
j. Metal rusts
k. Anantacid tablet fizzes and releases carbon dioxide gas when it comes in contact with hydrochloric acid in the stomach.

4. What is the main difference between physical changes and chemicalchanges?
- During a physical change the composition of matter never changes whereas in a chemical change the composition of matter always changes

5. In a chemical reaction, how does themass of the reactants compare with the mass of the products?
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6. According to the law of conservation of mass, when is mass conserved?
- It states that in any physical change orchemical reaction, mass is conserved.

7. Hydrogen and oxygen react chemically to produce water. How much water would form if 4.8 grams of hydrogen would react with 38.4 grams of oxygen?
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