Cumberland High School – Chemistry Name______________________________________________________
Introduction to chemical reactions Period_______ Date___________________________________
NOTES: Introduction to chemical reactions
TARGETS Represent a chemical reaction by writing a Chemical Equations. Balance Chemical Equations to show the same number of atoms of each element on
each side. Explain that a balanced chemical equation obeys The Law of Conservation of Mass
(saying that atoms won’t be created or destroyed in a chemical reaction.) Analyze a chemical equation. Identify the 5 basic types of chemical reactions,
reactants, products Identify signs of a chemical reaction from lab observations
Signs of a chemical reaction
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Representing Chemical Reactions
Chemists observe chemical reactions and have come up with a shorthand way to represent or model what is happening.
Word equations are written as _________________________________ by replacing
chemical names with correct __________________________________
Solid Sodium combines with Chlorine gas to make solid Sodium Chloride:
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Chemical equations
_____________________________ – starting substances in chemical reaction,
written on left side of arrow
_____________________________ – substance(s) formed from the reaction,
written on right side of arrow
_____________________________ à _____________________________
When more than one reactant or product they are separated with a _____________
The arrow à shows the ____________________________ of the reaction
Symbols used in chemical equations
Symbol Purpose
+ Separates more than one reactant or product
à Separates reactants from products. Indicates direction of reaction
(s) Identifies a solid state
(aq) Identifies that something is dissolved in water
(l) Identifies liquid state
(g) Identifies gaseous state
Law of Conservation of Mass
In a chemical reaction, matter is neither ___________________________________.
Atoms won’t ______________________________________________________
(e.g. a Carbon atom can’t become an Iron atom)
This means that you have to have the ___________________________________
_______________________ on each side of the chemical equation.
****After you write a chemical equation you have to balance it to make sure that the same number of atoms of each element are on each side. (law of conservation of mass)
Balancing a chemical equation
1. Write the Skeleton Equation
Li(s) + H2O(l) à H2 (g) + LiOH (aq)
2. Count the atoms of the elements in the reactants
1 atom Li, 2 atoms H, 1 atom O
3. Count the atoms of the elements in the products
1 atom Li, 3 atoms H, 1 atom O
4. Add whole number Coefficients to make the number of atoms of each element equal on
both sides of arrow
2Li(s) + 2 H2O à H2(g) + 2LiOH(aq)
5. Write the Coefficients in their lowest possible ratio
6. Check your work
Types of chemical reactions
_______________________________ – two or more substances combine to form
one product
_______________________________ – one substance breaks down into two or
more simpler substances
_______________________________ – one single element replaces another
_______________________________ – two compounds switch cations. Products
can be insoluble in water(precipitate)
_______________________________ - substance (hydrocarbon) combines with
oxygen to produce carbon dioxide and water and energy (exothermic)
Guided Practice