Matter and New Substances

• a change in the physical and chemical properties

• one or more NEW substances are formed

Chemical Change

• a change in physical properties only, such as size, shape, or state

• NO new substance is formed

​Physical Change

Review of Physical and Chemical

Changes in Matter

Water freezing and forming ice: 

H₂O (l)  ⟹   H₂O (s) 

 

No new substance is formed.  The exact same substance (compound) is on the left and the right.  This is a physical change. The letters in parentheses indicate a change in state from liquid (l) to solid (s). 

Hydrogen and oxygen react and bond producing water:

2H₂ + O₂  ⟹   2H₂O 

 

A new substance is formed: water.  The same number and types of atoms (elements) are on both sides, but the molecules (compounds) are different.  This is a chemical change. 

Multiple Choice

cutting paper into different shapes

• chemical change

• physical change

• no change

Multiple Choice

eggs cooking

• chemical change

• physical change

• no change

Multiple Choice

ice melting

• chemical change

• physical change

• no change

Multiple Choice

fireworks exploding

• chemical change

• physical change

• no change

As a class experiment,

​the students mixed baking soda and vinegar in a flask. They observed that the reaction produced bubbles and the temperature went from 25^oC to 10^oC.

Multiple Choice

What is the evidence of a chemical change when the baking soda was mixed with the vinegar?

• color change and bubbles

• temperature change and bubbles

• formation of a precipitate

• temperature change and formation of a precipitate

Multiple Choice

When vinegar and baking soda react, energy is needed to break bonds.  The reaction ABSORBS heat, which the students observed when the mixture drops in temperature.  Is the reaction between baking soda and vinegar endothermic or exothermic?

• endothermic

• exothermic

Multiple Choice

Lilly performs a lab about physical and chemical changes in her chemistry class.  She mixes sugar into water, until the sugar is completely dissolved.  Her lab partner Stephen thinks it is a chemical change, but Lilly disagrees. 

• They are both correct. It is a physical and a chemical change.

• Lilly is correct. Dissolving sugar in water is a physical change.

• Stephen is correct. Dissolving sugar in water is a chemical change.

• They are both wrong. No change occurred.

Multiple Choice

The metal of a nail reacted with oxygen and water, and formed a new substance called rust.

• This is a physical change.

• This is a chemical change.