7.1 Chemical reactions-2

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 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.

The production of carbon dioxide gas when baking soda and vinegar reacted indicated a _____________.

• Chemical change

• Physical change

What is essential for a combustion reaction to begin?

• Carbon dioxide
• Fuel 
• Fuel, oxygen and heat
• Water and oxygen

Another term for burning is

• Fire triangle
• Magnesium oxide
• Combustion
• Bustion