Chemical Changes
Ethan is observing chemical and physical properties of a substance. He heats a substance and observes that the substance turns from a brown solid to a black powder. He refers to several chemistry journals that claim this represents a chemical reaction. From his observation and research, he concludes that the substance goes through a chemical change when heated. How can Ethan best defend his conclusion?
By verifying that the substance is now made up of different molecules than before it was heated.
When sugar is added to water to make a sugar solution, a physical change occurs. According to the Law of Conservation of Mass, what prediction can be made about the mass after this physical change?
The sugar solution will have the same mass a s the sugar and water
What could you do with the temperature that would slow down a chemical reaction?
Decrease the temperature
A chemist measures the temperature at which a particular liquid boils. She makes the measurement a second time. Which of these is most likely described in this scenario? Is this repetition or replication
Repetition. She is doing her own experiment over again.
Grant takes a cold can of soda out of a refrigerator. He sets the cold can on a table in the room and leaves it there for a few hours. Which of the following best describes what will occur?
Heat from the air will move into the soda can until both reach the same temperature.
Steve fills a jar with water and adds Epsom salts and ammonia. After five minutes, he observes that white particles have formed and settled at the bottom of the jar. He isolates the white particles and finds that they have properties that are very different from any of the three starting materials. How does he know a chemical change occurred?
A new substance formed.
A chemist adds 50 mL of liquid A and 50 mL of liquid B to a beaker, with constant stirring. The reaction is going slowly. What could the chemist do to speed the reaction up?
Add heat to the reactions. For example, heat the beacker on a hot plate.
The melting of wax is a physical change, yet the burning of wax is a chemical change. What is the essential difference between a physical change and a chemical change of wax in a burning candle?
the burning of wax forms new compounds while the melting of wax does not.
In any chemical reaction, the mass of the reactants (what goes into the reaction) equals the mass of the products (what comes out of the reaction). For example, if you burn wood to cause a chemical reaction, the mass of the starting wood is equivalent to the mass of the resulting wood, ash, and smoke. This result forms the basis of the Law of Conservation of Mass. Which statement correctly explains why this is a law, rather than a theory?
It describes a repeatedly observed relationship (Law), but it does not offer an explanation (Theory)
What happens to the heat and state of matter of an ice cube when it is thrown into a fire?
The heat of the fire will be transferred to the ice, causing it to change its state.
An opened bottle of milk in a refrigerator stays fresh longer than one at room temperature on a table. Assuming that losing freshness is related to a chemical reaction, which statement best explains this event?
The lower temperature inside the refrigerator reduces the rate of the chemical reaction.