Unit 7 Chemical Reactions
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Transcript Unit 7 Chemical Reactions
Objectives
Write chemical equations to describe chemical
reactions
Balance chemical equations
Classify and identify chemical reactions
Predict products from chemical reactions
YouTube - ammonium dichromate volcano
YouTube - Nitrogen Triiodide Detonation
YouTube - Sodium and Water
YouTube - Reaction of Sodium & Chlorine (with
subtitles)
I. Reactions and equations
Evidence of a chemical reaction
Temperature change
Change in color
Evidence of chemical change
Gas production (bubbles, fizzing)
Appearance of a solid (precipitate)
Representing chemical reactions:
Reactants: starting substances (written on the left side)
Products: substances that result from the reaction
(written on the right side)
Symbols used in chemical equations
Symbol
Meaning
Yield (placed between reactants and products)
+
Separate two or more reactants or products
(s)
Substance is in a solid state
(l)
Substance is in a liquid state
(g)
Substance is in a gaseous state
(aq)
Substance is in an aqueous (water) solution
Heat is applied
Pt
A substance written above an arrow indicates it
is a catalyst needed for the reaction
Word equations: indicates the reactants and products
in a chemical reaction
iron(s) + chlorine (g) iron (III) chloride (s)
“iron and chlorine react to produce iron(III) chloride”
Word equations lack important information
Skeleton equations
Uses chemical formulas to represent reactants and
products
Fe (s) + Cl2 (g) FeCl3 (s)
Practice:
Write the skeleton equations for the following:
1. Hydrogen (g) + Bromine (l) hydrogen bromide (g)
2.
Carbon monoxide (g) + oxygen (g) carbon dioxide (g)
Practice:
Write the skeleton equations for the following:
1. Hydrogen (g) + Bromine (l) hydrogen bromide (g)
H2 (g) + Br2 (l) HBr (g)
Carbon monoxide (g) + oxygen (g) carbon dioxide (g)
CO (g) + O2 (g) CO2 (g)
2.
II. Balancing chemical equations
Chemical equations:
Must obey “law of conservation of matter”
Must show that the number of atoms of each substance
is the same before and after the reaction.
A chemical equation has to be BALANCED
To balance chemical equations, COEFFICIENTS (whole
number)are written in front of a reactant or product.
If coefficient is 1, it is not written
Steps for balancing equations
1.
Write the skeleton equation for the reaction. Ex.
Hydrogen gas reacts with chlorine gas and yields
gaseous hydrogen chloride.
H2 (g) + Cl2 (g) HCl(g)
2. Count the atoms of each substance for the reactants
and products.
REACTANTS
PRODUCTS
H:
H :
Cl :
Cl :
3. Place coefficients (ONLY IN FRONT OF A
REACTANT OR PRODUCT) to make number of
atoms of each element equal on both sides of the
equation. (#atoms= coefficient x subscript)
H2 (g) + Cl2 (g) HCl(g)
REACTANTS
PRODUCTS
H:
H :
Cl :
Cl :
4. Write coefficients in lowest ratio possible
H2 (g) + Cl2 (g) HCl(g)
5. Check your answer.
REACTANTS
PRODUCTS
H:
H :
Cl :
Cl :
Practice
1. Write a balanced chemical equation if magnesium
bromide reacts with chlorine and yield magnesium
chloride and bromine.
2. Write a balanced chemical equation for:
Potassium nitrate potassium nitrite + oxygen
3. Balance the following reaction
CaO + H2O Ca(OH)2
4. Reactions for gummy bear sacrifice
KClO3 KCl + O2
C12H22O11 + O2
C + CO2 + H2O