Chemical Reactions

Chemistry: the study of matter

and how it changes.

Molecules and Compounds: Combinations of atoms
in specific proportions.

What are Properties?

What are Properties?

The qualities and characteristics that

What are Properties?

describe and identify a substance.

What are Properties?

Ex. color

density

taste

texture flexibility

Compounds and Molecules:

The properties of the compounds and molecules are

Ex:

different than the elements that make them.

Ex:

Na

+

Cl

NaCl

different than the elements that make them.

Ex:

Na

+

Cl

NaCl (salt)

explosive

poisonous

yummy

Chemical Reaction: rearranging atoms to form one

or more new substances.

Evidence of a chemical reaction:

Evidence of a chemical reaction:

2 Types of Reactions:

1. Exothermic: Energy is released in the reaction

in the form of heat and/or light.

Ex:

candle burning

hand warmers

elephant toothpaste

Heat and light are forms of energy.

Where did the energy come from?

It was stored in the chemical bonds.

What had to be done to release it?

Chemical reactions

2. Endothermic: energy is absorbed in the reaction.

light

(energy)

Ex:

photosynthesis

cold packs

light

(energy)

Chem RX

Chemical
Reactions

Law of Conservation of Energy: Energy cannot be

created or destroyed

but it can be transformed (or change form)

Energy comes from energy and goes to energy.

Energy going into a chemical reaction must equal
energy produced.

Law of Conservation of Mass:

Matter comes from matter and goes to matter.

Ex. Wood

CO2 H2O O2

C, H & O

Released
Carbon ashes

Matter cannot be created or destroyed but it can change form

100g HgO

92.6g Hg + 7.4g O2

Conservation of Mass

Chemical Equation: The written form of a chemical
reaction

form

Reactants

Products

REVIEW...

What is a Chemical Formula?

Aspirin

Table sugar

Dynamite

C7H6O3 C12H22O11 C7H5N3O6

Chemical Formula: Symbols and numbers that tell the
elements present and the number of atoms of each
element in each molecule.

Aspirin

Table sugar

Dynamite

C7H6O3 C12H22O11 C7H5N3O6

Subscripts tell the number of atoms of each element

in a molecule. C6H12O6

Aspirin

Table sugar

Dynamite

C7H6O3 C12H22O11 C7H5N3O6

Aspirin

Table sugar

Dynamite

C7H6O3 C12H22O11 C7H5N3O6

EVERY MOLECULE HAS DEFINITE PROPORTIONS.

Balancing Chemical Equations

You must pay attention to subscripts and coefficients

Glucose

7C6H12O6

Coefficient -
The number
in front of the
formula

Coefficient: The number in front of the formula.

2 H2O

3 H2SO4
7 NH4

Tells the number of molecules in a chemical
equation.

2 H2O

3 H2SO4
7 NH4

2 H2O

3 H2SO4
7 NH4

Coefficient X Subscript = the number of atoms of that

element

The number of atoms of each element

must be equal on both sides of the equation

Quick Monday Review 10/30

1. Chemistry studies ____ and how it ____.
2. The qualities and characteristics that identify a substance are

its _____

3. Give 2 evidences of a chemical reaction.
4. What kind of reaction releases energy?
5. What law says you cannot create or destroy matter?
6. What is on the left side of a chemical equation?
7. What is on the right side of a chemical equation?
8. What tells the number of atoms of elements in a molecule?
9. What tells the number of molecules in an equation?

10. Is this equation balanced? 2AlO3H3

Al2O3 + 3H2O

The correct way to write chemical formulas.
H2O1 or

H2O ??

C1O2
or

CO2 ??

Is this chemical equation balanced?

2

Count the atoms of each element on each side.

Al=2

O=2

Al=2

O=3

2

Change the coefficients until the numbers of atoms
of each element on each side of the equation are =

2

Continue until ALL the numbers of atoms are equal.

Writing Chemical Equations for Chemical Reactions:

1. Use chemical formulas for

O2 Al2O3

Writing Chemical Equations for Chemical Reactions:

reactants and products.

Writing Chemical Equations for Chemical Reactions:

2. Use coefficients to show the number of

Writing Chemical Equations for Chemical Reactions:

molecules of each substance needed.

Chemical equations must balance

BECAUSE…..

in kind and number of atoms

BECAUSE…..

between reactant and products

BECAUSE…..

between reactant and products

BECAUSE….. The Law of ???? of ???

between reactant and products

BECAUSE….. The Law of Conservation of Mass

PRACTICE: Is this chemical equation balanced?

P + O2

P2O5

Count the atoms of each element on both sides.

P + O2

P2O5

P=

O =

P =

O =

P + O2

P2O5

P= 1

O = 2

P = 2

O = 5

Change the coefficients until the numbers of atoms of
each element on each side of the equation are =
P + O2

P2O5

P= 1

O = 2

P = 2

O = 5

P + O2

P2O5

P= 1

O = 2

P = 2

O = 5

Continue until ALL the numbers of atoms are equal.
P +5O2

2P2O5

P= 1

O = 2

P = 4

O = 10

4P + 5O2

2P2O5

P= 4

O = 10

P = 4

O = 10

Steps for Balancing Chemical Equations:

1. Count the number of atoms

Steps for Balancing Chemical Equations:

of each element on both sides of the equation

coefficient X subscript = total number of atoms

REMEMBER

You CANNOT change a subscript.

F2O3
F4O6

You CAN change a coefficient.

REMEMBER

You CAN change a coefficient.

2. If the number of atoms are NOT equal on both sides,

start balancing by changing the coefficient in front of

the molecules from left to right.

3. Continue until ALL the numbers of atoms are
equal.

Balancing Equations Quick Review

Write the 2 equations on your paper and balance them.

1. H3PO4 + KOH → K3PO4 + H2O

2. Rb + S8 → Rb2S

ENDOTHERMIC AND EXOTHERMIC REACTIONS!!

Define endothermic:

Define exothermic:

Materials: thermometer / cups / H2O2 and yeast,
baking soda and vinegar

ENDOTHERMIC AND EXOTHERMIC REACTIONS!!

Procedure: Plan your experiment and write it in steps.

One of the combinations of materials is endothermic
and the other is exothermic. Your job is to do a
controlled experiment, make accurate measurements
and record data to show which reaction is exothermic
and which one is endothermic.

Include a chart and graph in your data and analysis so
make multiple measurements.

Example of what you write:

H2O2 and yeast:

1. Measure 10ml of H2O2 and pour it into the cup.

Example of what you write:

H2O2 and yeast:

1. Measure 10ml of H2O2 and pour it into the cup.
2. Measure and record the temperature of the H2O2
3. Measure….

Lab Data:

Endothermic reaction: Starting temperature:

Ending temperature:

Difference:

Data and Analysis:

Make a graph of your data from each experiment. Be
sure to label the X and Y axes and correctly number
the lines. Plot your data points on the lines. Title your
graph with the type of reaction that occurred.

Data and Analysis:

1. For each reaction answer the following questions.

Endothermic:

a. Give 2 evidences that a chemical reaction occurred.
b. State your evidence that it was endo or exothermic.

Exothermic:

a. Give 2 evidences that a chemical reaction occurred.
b. State your evidence that it was endo or exothermic.

Data and Analysis:

2. Which reaction had a greater temperature change?
3. Tell at least 2 differences in the trends in the data
between the endothermic and the exothermic reactions.
(What do I mean by “trend”?)

4. Tell 2 ways the endothermic and exothermic reactions
were like each other?

5. How did you think you would do “planning” your own
lab on another lab activity? Tell reasons for your answer.

Endothermic and Exothermic Reactions:

In chemical reactions,

energy is required to
break the bonds in

Endothermic and Exothermic Reactions:

the react

the reactants so the
atoms can be

Endothermic and Exothermic Reactions:

rearranged to make
the products.

Energy is added to break bonds and separate
atoms.

Energy is released when bonds are formed.
(Remember why atoms bond?)

(Remember why atoms bond?)

Atoms make bonds because it

TAKES LESS ENERGY!

Endothermic Reactions:

If the energy required to
break the bonds is

GREA

Endothermic Reactions:

in the reactants is

Endothermic Reactions:

GREATER than the energy
released

Endothermic Reactions:

when making new bonds,
in the products

Endothermic Reactions:

the reaction is
ENDOthermic.

Endothermic Reaction:

Example: (Write either the formulas OR the words.)

HC2H3O2 + NaHCO3 NaC2H3O2 + CO2 + H2O

Vinegar + Baking soda

Sodium acetate + Carbon dioxide +Water

HC2H3O2 + NaHCO3 NaC2H3O2 + CO2 + H2O

GREATER energy
used to break
bonds in the
reactants.

HC2H3O2 + NaHCO3 NaC2H3O2 + CO2 + H2O

GREATER energy
used to break
bonds in the
reactants.

LESS energy released
when making bonds in the
products.

Exothermic Reactions:

If the energy required to
break the bonds

Exothermic Reactions:

in the reactants is

Exothermic Reactions:

LESS than the energy
released

Exothermic Reactions:

when making new bonds

in the products,

Exothermic Reactions:

the reaction is
EXOthermic.

Exothermic Reaction:

Example: (Write either the formulas or words.)

2 H2O2 2 H2O + O2

(hydrogen peroxide) (water) (oxygen)

2 H2O2 2 H2O + O2

LESS energy
used to break
bonds in the
reactants.

2 H2O2 2 H2O + O2

LESS energy
used to break
bonds in the
reactants.

GREATER energy
released when
making bonds in
the products.

Rates of Reaction

The rate of a chemical reaction tells us how fast
reactants are turned into products.

Fast rate of reaction: Examples

Slow rate of reaction: Examples

Fruit rotting

metal rusting

newspaper aging

Rates of Reaction Lab:

What was your hypothesis?

Why did you make that hypothesis?

What are particle collisions?

What do they have to do with reaction rates?

Rates of Reaction Lab:

7b. The reaction rate should have been fastest in
hot water.

Is that what your data showed? Yes or No
If it wasn’t, what caused your mistake?

Collision Theory:

Reactions can only take place when particles collide
with enough energy to react.

Activation energy: The smallest amount of energy
needed before particles will react.

4 main factors that affect rates of reaction:

1. Surface area: more surface area increases the

rate of reaction

Allows for more collisions

small particles = more surface area = more collisions

2. Catalyst: a substance that makes particles collide
more often or lowers the activation energy - speeds
up rate of reaction

Hydrogen peroxide
(H2O2) naturally
decomposes into
H2O and O2.
Yeast is a catalyst
that speeds up the
reaction.

3. Concentration: higher concentration makes
particles more crowded and causes more collisions

higher concentration = more particles = more
collisions

4. Temperature: higher temperature makes particles
move faster

so there are more collisions with more energy

For every 10o temperature increase the rate of
reaction doubles.

higher temperature =

high energy =

fast movement =

lots of collisions

The amount of the reactants affects the amounts
of the products.

If reactants are not in correct amounts, the
amounts of the desired product is less.

Undesired products are called byproducts.

If a reactant is less than required it is called a
limiting reagent.