4.1 - Intro to Chemical Reactions

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

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.

What type of change do we see in when we melt ice?

• Physical Change
• Chemical Change

This is used to represent the number of each atom being represented. 

• An exponent
• The coefficient
• A molecule
• The subscript

This appears on the left side of a chemical formula, and represents how many molecules there are. 

• An Atom
• The Subscript
• A Molecule
• The Coefficient

A physical change is?

• It changes the object into something different
• Objects or substances undergo a change that does not change their chemical composition
• it is just like a chemical reaction
• Paper burning