Recognizing Chemical Reactions Flashcards
Which of the following correctly describes changes in energy during a chemical reaction?
Energy may be either absorbed or released during a reaction.
If you mix two clear, colorless liquids together, which of the following observations would indicate a chemical reaction has occurred?
A solid appears in the tube and settles to the bottom.
A solid and a liquid are mixed in a test tube. Which of the following observations would indicate that a chemical reaction occurred between them?
The test tube becomes colder as the substances are mixed.
The mixture changes color to a deep blue.
The mixture starts to fizz as a gas is released.
Which of the following may indicate a change in the chemical properties of matter?
Both A and B
When two colorless _____ are mixed together, the formation of a solid precipitate is a strong indication that a chemical ___ has occured
liquids; reaction
When zinc metal is mixed with hydrochloric acid, vigorous production of what substance is an indication that a chemical reaction is occurring?
hydrogen gas
Two reactants are mixed in a test tube, and the test tube becomes very warm. This is a sign of a transfer of _____ taking place as a result of a chemical change.
energy
A solid that forms and settles out when two or more solutions are mixed is called a _____.
precipitate
If a powdered solid were mixed with a liquid which of the following observations would most clearly indicate a chemical reaction was occurring?
The mixture starts fizzing and releasing gas.
Someone is working in their garden, giving some plants a liquid fertilizer to help them grow. They accidentally spill some of the fertilizer on a rock in their garden and notice the rock appears shiny and a little darker than it did when it was dry. After a while the rock dries and looks the same as it did before being covered in fertilizer.
This likely means a chemical reaction has occurred between the rock and the fertilizer.
false
A sample of metal is heated until it melts and begins to glow red. When it cools it appears the same as it did before it was heated.
This is strong evidence that a chemical reaction has occurred.
false
A small piece of silvery metal is added to a large beaker of water and immediately erupts into flame. This is evidence that a chemical reaction is occurring.
true
A liquid in a container is heated until it turns to a gas. This is enough evidence to determine that a chemical reaction occurred.
false
If you heat a red powder to a high temperature and observe that it changes to a silver color and remains that way when it cools, this would be good evidence that a chemical reaction has occurred.
true
When a color change happens, a chemical reaction must have occurred.
true
