chemical reactions - denton independent school district · exit ticket: 3-2-1 chemical reactions...
TRANSCRIPT
Chemical Reactions
Law of Conservation of Mass
Matter can not be
created or
destroyed, although
it may be
rearranged.
Lavoisier, 1788
Chemical Reactions change that occurs when atoms
rearrange themselves
A process in which one or more substances are changed into others
Chemical Reaction
•How do you know if a chemical reaction has occurred?
Creation or loss
of heat
• Anytime two
chemicals are
combine resulting in a
temperature change,
that is evidence that
heat is being added or
lost from the products
and a chemical
reaction had occurred.
Evidence of Chemical Reactions
•Temperature Change
•Heat is absorbed by the substances causing the temperature to decrease
•Heat is released by the substances causing the temperature to increase
Production of a gas
(bubbles)
• When you mix chemical and see
bubbles or foaming, that is
evidence that a new gas has
formed
• This is a new substance which
means that a chemical reaction
must have occurred
• The only exception is when you boil
a liquid by adding heat
Evidence of Chemical Reactions
•Fizzing
•When a gas is formed it may try to escape causing bubbles
Evidence of Chemical Reactions
•Color Change
•This is evidence of a chemical reaction only when the other properties have also changed.
Chemical
Change
Not a
Chemical
Change
Evidence of Chemical Reactions
•Precipitate Formed
•Precipitate is a solid substance formed when liquids are combined
•Example – Sour Milk Clumps
Evidence of Chemical Reactions
•Light
•When a new substance is formed light energy can be produced.
Other Signs That a Chemical Reaction has occurred •Fire
•Rotting
•Breaking down (decomposition)
•Cooking
•Rusting (oxidation)
What chemical reactions have you experienced???
EXIT TICKET: 3-2-1 Chemical Reactions
• 3: Types of evidence that proves that a chemical change has occurred
• 2: Examples of chemical reactions
• 1: Way that chemical reactions are different than physical changes.