Signs of Chemical Reactions
A liquid begins bubbling and releases gas after two substances are mixed. What does this MOST likely indicate?
A chemical reaction.
What does the periodic table organize?
Elements.
Rust forming on metal is what type of change?
Chemical Change
During a chemical reaction, atoms are ____.
rearranged
What phase change occurs when liquid water becomes gas?
Evaporation
Why is a color change sometimes evidence of a chemical reaction?
A new substance may have formed.
What does the symbol “O” represent?
Oxygen
Breaking a pencil is considered what type of change?
Physical Change
True or False: Atoms disappear during chemical reactions. (EXPLAIN YOUR ANSWER)
False: Atoms are not created or destroyed, just rearranged.
What happens to particle motion when heat is added?
The particles move faster.
A student melts ice and says a chemical reaction occurred. Why is the student incorrect?
Melting is a physical change because no new substance forms.
Why do scientists use chemical symbols instead of full element names?
Symbols are shorter and universally recognizable.
A student dissolves sugar in water. Why is this NOT a chemical reaction?
No new substance forms
Hydrogen and oxygen combine to form water. What happened to the atoms?
They rearrange to form a new substance (2 hydrogens bond with 1 oxygen).
Why is freezing considered a physical change?
The substance stays the same, just changes from a liquid to a solid.
Bread baking in an oven produces new smells and colors. Is this an example of a physical change or a chemical change?
A chemical change.
Carbon dioxide is an example of a compound, it contains carbon and oxygen. What is a compound?
Compounds are made from multiple elements chemically combined.
Which situation is MOST likely a chemical change: tearing paper, boiling water, burning wood, or melting wax?
Burning Wood
Why must the number of atoms stay the same before and after a reaction? Which LAW in science supports this idea?
Law of Conservation of Matter: matter is never created or destroyed.
Compare a phase change to a chemical reaction.
Phase changes do not form new substances; chemical reactions do.
A reaction causes temperature to increase without adding outside heat. What does this suggest?
Energy was released during a chemical reaction.
Which element has the symbol "Al" on the periodic table? SPELLING MATTERS...
Aluminum
Is a phase change an example of a chemical change or a physical change? How do you know?
Physical change, because melting, freezing, boiling, etc. do not create a new substance. It only changes the form of a substance (solid, liquid, gas).
A scientist observes a combustion (explosion) in his laboratory when he combines two chemicals. He states, "Some of the atoms in this reactions were destroyed in this severe explosion." Is his claim correct? How do you know?
Atoms/Matter are not destroyed in a reaction, regardless of what happens. Atoms are only rearranged.
A student says evaporation and burning paper are both chemical changes because both involve energy. Explain why this is incorrect.
Evaporation is a physical change; burning paper forms new substances and is chemical.