This document discusses chemical and physical changes in matter. It defines chemical properties as those that describe a substance's ability to change into a different substance through a chemical reaction. Physical properties can be observed without a chemical change. Chemical changes result in new substances, while physical changes only alter the form or appearance. Evidence of a chemical change includes a change in properties or energy, with energy either absorbed or released. Chemical equations are used to represent chemical reactions and their reactants and products. The mass of reactants and products is conserved in any chemical change.
3. Observing Chemical Change
• Chemical Properties: The
characteristics of a substance that
describes it’s ability to change into a
different substance.
– EXAMPLE: In our magnesium lab, we lit
the magnesium on fire, watched it burn
as it reacted with the oxygen in the air.
This was its chemical property:
flammability.
4. Observing Chemical Change
• Physical Properties: a characteristic
of a substance that can be
observed without changing the
substance into something new.
– EXAMPLE: Frozen water (ice) melts at 0
degrees Celsius. The tops of the tables
in this room are black and 4.5ft long.
5. Observing Chemical Change
• Like the properties of matter, the
changes it undergoes can be:
– Physical Changes
OR
– Chemical Changes
6. Observing Chemical Change
• Physical Changes: Any change that
alters the form, shape, or
appearance of a substance but
does not change it into a new
substance.
– EXAMPLE: If I were to toss fresh berries
into a blender and make a fruit
smoothie- it would still be fruit, just
mashed into smaller pieces.
7. Observing Chemical Change
• Chemical Changes: a change that
a substance undergoes where a
totally new substance is the result.
– EXAMPLE: In the magnesium lab, we
burned magnesium and after it’s
chemical change the result was
magnesium oxide. It was no longer
metal!!
8. Observing Chemical Change
• During a chemical change you
have:
– Reactants: the substance that is being
changed.
– Products: the new substance formed as
a result of the chemical reaction.
9. Observing Chemical Change
• REMEMBER: in order for a chemical
reaction to have occurred- bonds
must be broken and new bonds
must be made!!!
10. Observing Chemical Change
• EVIDENCE that a CHEMICAL
REACTION has occurred:
– Change in properties
– Change in energy
11. Observing Chemical Change
• Change in properties: color change,
a solid forms (precipitate), formation
of gas, and texture change.
• CAUTION!! Sometimes physical
changes make it SEEM like a
chemical change has occurred.
Really THINK about the changes.
12. Observing Chemical Change
• Change in Energy: During chemical
changes, energy is either absorbed
or released.
– Endothermic reactions (heat enters)
– Exothermic reactions (heat exits)
• (remember those words…??)
13. Describing Chemical Changes
• Chemical equations are used to
show/explain a chemical reaction.
– This shows the reactants and products
of a reaction
– They show the substances you start
with, on the left and the new
substances on the right separated by
an arrow.
15. Conservation of Mass (matter)
• During Chemical reactions, atoms
cannot be created OR destroyed.
• The total mass of the reactants must
equal the total mass of the
products.
16. Conservation of Mass (matter)
• In a chemical reaction, the number
of atoms stays the same- they are
just rearranged. Therefore, the
number of atoms in the reactants
are the same as the number of
atoms in the products.
17. Open and Closed System
• Sometimes it’s hard to understand
where the matter comes from in a
reaction.
• Matter can either come from an…
– Open System
or a…
– Closed System
18. Open and Closed System
• Open System: Matter can enter from
or exit into the surroundings during a
reaction.
• Closed System: Matter cannot enter
or leave during the reaction.
