Chemical
Reactions
and
Equations
How can you tell if a chemical
reaction has occurred?
1)
2)
3)
4)
5)
Color change
Heat produced/gets warm (exothermic)
Heat absorbed/gets cold (endothermic)
Gas produced (fizz)
Solid produced/turns cloudy (precipitate)
These are indications of
CHEMICAL CHANGES
Physical Changes….
DO NOT tell you a chemical reaction has
occurred!
Examples of physical changes:
Phase changes (solid-liquid-gas)
Changes in shape
Is a chemical reaction occurring?
Is a chemical reaction occurring?
Is a chemical reaction occurring?
Is a chemical reaction occurring?
Is a chemical reaction occurring?
Is a chemical reaction occurring?
Is a chemical reaction occurring?
Is a chemical reaction occurring?
Is a chemical reaction occurring?
Chemical formulas…
are the “words” in the language of chemistry
In the last unit you learned how to name
compounds and write their formulas. You
learned chemistry “words” like
KNO3
and
NaBr
Chemical Equations…
are the “sentences” in the language of chemistry.
You will put together the “words” (formulas) you
learned in the last unit to make “sentences”
(chemical equations)
As in English, “sentences” are more interesting
and give you more information than isolated
“words”
“Punctuation and grammar”
In addition to needing “words” in your
“sentences”, you will also need some
punctuation and grammar to so your
sentence makes sense and is easy to
understand.
Every chemical equation (sentence) has
formulas (words) as well as special
symbols (punctuation)
Symbols used in Chemical
Equations
+
and
yields
a gas forms
a precipitate forms
Heat needed (reaction is endothermic)
More symbols
catalyst
a catalyst is needed
(s)
Solid phase
(l)
Liquid phase
(g)
Gas phase
(aq)
aqueous (dissolved in water)
“Grammar”
Some basic rules for putting your chemical
equations together correctly:
1) Like in English, always read from left to
right across the page
Start here ……………………………end here
“Grammar”
Some basic rules for putting your chemical
equations together correctly:
2) Each equation has two halves. The half
left of the arrow is the REACTANT side.
The half right of the arrow is the PRODUCT
side.
REACTANTS
PRODUCTS
Chemical equations are easy!
(compared to English!)
You now know everything you need to know
to write “grammatically correct” chemical
equations
Word Equations
Translate the following word equation into an
chemical equation:
Hydrogen chloride in the liquid phase and
sodium hydroxide in the solid phase yields
aqueous sodium chloride and water
Word Equations
Hydrogen chloride in the liquid phase and
sodium hydroxide in the solid phase yields
aqueous sodium chloride and water
HCl (l) + NaOH (s)
NaCl (aq) + H20