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:

____________________________________________________________________

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