Chem

CONCEPT 1 OBJECTIVES

Differentiate between physical and chemical

changes.

Explain the collision theory.

List several signs that can provide evidence that a

chemical reaction has occurred.

Explain the Law of Conservation of Mass and how it

relates to chemical reactions.

Differentiate between coefficients and subscripts in

a chemical reaction.

CONCEPT 1 OBJECTIVES

6. Be able to label, interpret, and write equations for

chemical reactions with correct notation.

7. Be able to balance chemical reactions according to

the Law of Conservation of Mass.

8. When given a written description of a reaction, be

able to write the balanced chemical reaction for it.

Vocab.

Chemical reaction

Reactants

Products

Aqueous

Chemical Reactions

Physical change: change in a substance that

doesn’t change its identity

Ex. Boiling, melting, vaporizing, grinding, etc.

Chemical change: change of a substance into

another substance; when a chemical reaction

occurs

Ex. Burning, oxidizing, rotting, fermenting, etc.

Chemical reaction: process by which substances

collide with enough energy that new bonds are formed

between atoms, thus creating new substances.

Do NOT have a change in matter.

Do have a change in energy.

Chemical Reactions

Collision theory: Reacting particles must

collide in order for a chemical reaction to

occur

AND do it with enough force to change

something.

Meaning that they CAN collide without actually

reacting if there isn’t enough energy

The rate of a chemical reaction depends on the

frequency of the collisions.

Chemical Reactions

When a chemical change occurs, a chemical

reaction occurs.

Evidence of a chemical reaction:

Energy change in the system

Ex. Release of light

Ex. Heat released or absorbed, 🡪 a sudden

temperature change

Sudden color change

Odor change

Gas release

Sudden appearance of a solid

The solid that forms is known as a

precipitate

Law of Conservation of Mass

Law of Conservation of Mass: matter cannot be

created or destroyed – it can only change forms.

This is true even in a chemical change/reaction!

Ex. If there are 25 g of reactants, there must be 25 g

of products made.

Ex. If there are 2 oxygen atoms in the reactants, there

must be 2 oxygen atoms in the products.

This is where learning to balance equations becomes critical!

mass of reactants = mass of the products

(ingredients)

(results)

Writing Equations

Equations represent chemical reactions.

They can be written in word form or formula

form.

Example of words:

Hydrogen gas and oxygen gas react to form liquid water.

Example of formulas:

2H2 (g) + O2 (g) 🡪 2H2O (l)

Writing Equations

The notation used to represent reactions

2Na(s) + Cl2(g) 🡪 2NaCl(s)

Reactants = starting substances; “ingredients”

Products = ending substances; what is made

+ = separates one or more reactants or

products

🡪 = yields; produces

Reactants

Products

🡪

+

Writing Equations

The notation used to represent reactions

2Na(s) + Cl2(g) 🡪 2NaCl(s)

Coefficient = tells us the number of each

substance needed

These can change! The subscripts cannot.

If only 1 is needed, the 1 is not written (Ex. Cl2)

How to read this: the ratio of sodium to chlorine

is 2:1 in this reaction.

2

2

2

Writing Equations

The notation used to represent reactions

2Na(s) + Cl2(g) 🡪 2NaCl(s)

The other notation represents the state of

matter of each substance.

(s) = solid

(l) = liquid

(g) = gas

(aq) = aqueous

This means dissolved in water

(s)

(s)

(g)

Writing Equations

Putting it all together…

2Na(s) + Cl2(g) 🡪 2NaCl(s)

2 solid sodium atoms

reacts with

1 chlorine gas molecule

to yield

2 solid sodium chlorides

Sodium chloride reacts with silver nitrate to

produce silver chloride and one sodium nitrate.

When solid copper reacts with oxygen gas it

produces solid copper (II) oxide.

NaCl + AgNO3 🡪 AgCl + NaNO3

Cu(s) + O2 (g) 🡪 CuO(s)

Practice Time!

Write the following word equations into formula equations using

the appropriate notation.

Note: It is okay if it isn’t balanced! We will learn that next.

LiCl + O2 🡪 LiClO3

AlBr3 (aq) + K2SO4 (aq) 🡪 KBr(s) + Al2(SO4)3 (aq)

Lithium chloride and oxygen gas react to make

lithium chlorate.

Aqueous aluminum bromide reacts with aqueous

potassium sulfate to produce solid potassium bromide

and aqueous aluminum sulfate.

Practice Time!

Write the equations in words. Make sure to correctly name each

substance.

Note: It is okay if it isn’t balanced! We will learn that next.

Balancing Equations

Equations must be balanced to keep from

violating the Law of Conservation of Mass.

Coefficients are used to balance equations.

Why?

Because they can be changed…

…but subscripts cannot!

2Na(s) + Cl2(g) 🡪 2NaCl(s)

Steps to Balance Equations:

Write the equation for the reaction.

(This may already be done for you!)

Put the symbols of each element in a column

under the reactants and products.

(keep polyatomic ions together, if possible)

Count the number of each atom on both sides

of the equation, and write it in your chart.

Change the coefficients only on either side of

the equation to balance the number of each

atom.

Reduce coefficients, as needed.

(These must be written in the lowest whole number ratio!)

Chemical reactions can generally be

classified into one of 5 categories:

Synthesis

Decomposition

Combustion

Single Replacement

Double Replacement

We classify them so that it is easier to predict

the products for a reaction.

Synthesis

2 or more reactants combine to form a new

compound.

A + B 🡪 AB

Ex. 2Na(s) + Cl2(g) 🡪 2NaCl(s)

When an element combines with oxygen, it

produces an oxide (a binary compound with at least

1 atom of oxygen)

Ex. C(s) + O2(g) 🡪 CO2 (g)

Certain metal oxides combine with nonmetal oxides

to make salts (a compound made of cations and

anions)

Ex. CaO(s) + SO2(g) 🡪 CaSO3(s)

Composition, Combination, Formation Rxns

Decomposition

1 reactant produces 2 or more simpler

compounds.

AB 🡪 A + B

Ex. Ca(OH)2(s) 🡪 CaO(s) + H2O(g)

Most only take place when energy (in the

form of heat or electricity) is added.

Electrolysis = the decomposition of a substance

by an electric current

Ex. 2H2O(l) 🡪 2H2(g) + O2(g)

electricity

Δ

Combustion

When a substance reacts with oxygen.

Often produces a lot of energy in the form of

heat and light.

reactant + O2 🡪 product

Ex. 2H2(g) + O2(g) 🡪 2H2O(g)

Many combustion reactions occur with a

hydrocarbon, and result in carbon dioxide and

water.

Hydrocarbon = a compound made of carbon and

hydrogen

Fuel + O2 🡪 CO2 + H2O

Ex. CH4(g) + 2O2(g) 🡪 CO2(g) + 2H2O(g)

Single Replacement

When one element replaces an element like it

in a compound.

A + BC 🡪 B + AC

Ex. 2Al(s) + 3Pb(NO3)2(aq) 🡪 3Pb(s) + 2Al(NO3)3(aq)

Ex. Cl2(g) + 2KBr(aq) 🡪 Br2(l) + 2KCl(aq)

Many take place in an aqueous solution.

The most reactive metals can react with

water to produce metal hydroxides and

hydrogen.

Ex. 2Na(s) + 2H2O(l) 🡪 2NaOH(aq) + H2(g)

Single-Displacement or Single Exchange Rxns

Double Replacement

When the ions of two compounds exchange

places in an aqueous solution to form 2 new

compounds.

AB + CD 🡪 AD + CB

One of the resulting products is usually a:

Precipitate: an insoluble solid that forms from the ions

of two aqueous compounds

Ex. NaCl(aq) + AgNO3(aq) 🡪 AgCl(s) + NaNO3(aq)

Insoluble gas (seen as bubbles given off)

Ex. FeS(s) + 2HCl(aq) 🡪 H2S(g) + FeCl2(aq)

Molecular compound like water

Ex. HCl(aq) + NaOH(aq) 🡪 NaCl(aq) + H2O(l)

Double-Displacement or Double Exchange Rxns

Predicting Products

Some elements react more readily than

others.

Activity series: a list of elements in the order

in which they will easily undergo certain

chemical reactions

Metals that have a greater activity means they

lose e- more easily.

Nonmetals that have a greater activity means

they gain e- more easily.

Elements can replace any element below them

but NOT above them.

Reactions can be reversible.

2SO2(g) + O2(g) 🡪 2SO3(g)

2SO3(g) 🡪 2SO2(g) + O2(g)

When the forward and reverse processes

are happening at the same rate, we say

that the system is in equilibrium.

Indicated by a double arrow.

Chemical Equilibrium

Le Chatelier’s Principle

Le Chatelier’s Principle

Stress = Exercise adds CO2

Shift = the rxn shifts to the reactants

H2CO3 starts to build up in the bloodstream,

increasing the acidity of the blood.

In response, as you exercise, the body starts to

breath rapidly, removing CO2 from the bloodstream.

Stress = Breathing faster removes CO2

Shift = the rxn shifts to the products.

Factors that Affect

Equilibrium

Concentration change

The adding or removing of a reactant or product

Add reactant (either A

or B)

Add product (AB)

Remove reactant

(either A or B)

Remove product (AB)

Forward rxn favored

Reverse rxn favored

Reverse rxn favored

Forward rxn favored

Stress

Response

Factors that Affect

Equilibrium

Factors that Affect

Equilibrium

Pressure change (in gases)

If pressure is increased, the rxn will favor

whichever direction produces fewer gas

molecules

If pressure is decreased, the rxn will favor the

direction that produces more gas molecules

Factors that Affect

Equilibrium