Chemical Reaction Signs

Evidence of a chemical reactions is anything that shows - 

• a new substance has formed

• a solid dissolved in a liquid

• interaction between 2 gases

• a change in the state of matter

One of the signs of a chemical reaction taking place is:

• Bubbles are produced 

• Reactants are not combining

• Products are not forming

• Color is not changing

Which of the following describes a precipitate?

• a liquid forms when a block of metal is heated

• a solid forms when one liquid is poured into another

• a gas forms when a solid is placed in a liquid

• bubbles form when an acid is poured on a rock

Which is NOT an indication of a chemical change?

• temperature change

• formation of a precipitate

• shape change

• production of light

You know you a chemical reaction has occurred if 

• there is a precipitate.

• there is a color change.

• there is a temperature change.

• All of these answers are evidence.

A clear liquid from a flask is poured into another clear liquid in a beaker. Which of the following results of this procedure would indicate a new substance was formed?

• The level of the substance in the beaker is higher after the other liquid is added.

• A yellow solid forms and then settles to the bottom of the beaker.

• Small white crystals are left behind in the flask that held the first liquid.

• The mass of the combined liquids is greater than either original liquid.

Which of the following is an example that includes evidence of a chemical reaction?

• A sample of zinc is placed in water and it settles to the bottom

• A solid block of ice is heated and it completely melts into a liquid. 

• Sugar that is burned gives off an odor and turns brown and then black.

• A tomato is placed into a blender and chopped up into smaller pieces.

A student places a piece of a potato into a container of hydrogen peroxide. One observation the student makes is that bubbles form around the potato. The presence of bubbles might indicate the formation of a new substance because bubbles - 

• could show that a gas is forming.

• always rise to the top of a liquid. 

• are almost always perfectly spherical.

• usually burst after a few minutes.

How many elements are in C₆H₁₂O₆?

• 24

• 432

• 3

• 1

How many oxygen atoms are in this chemical formula?

• 7 oxygen atoms

• 4 oxygen atoms

• 3 oxygen atoms

• 1 oxygen atoms