6 March 2013
Give an example of a physical change and a
chemical change, and then describe how
they are different from the other. Explain
your answer in 2-3 sentences.
Standards 8.5.c.
I know chemical reactions usually liberate or
absorbs heat.
When chemical reactions occur, the
connections between atoms must be
broken and rearranged. In order to do
Heat
this, ________________
is involved in
all chemical reactions.
Endothermic
• Within-Heating
• Endo = Enter
• Therm/ic = Heat
Exothermic
• Outside-Heating
• Exo = Exit
• Therm/ic = Heat
Endothermic
Exothermic
• Reactions in
which the
system absorbs
heat from the
surrounding.
• Reactions in
which the
system releases
heat to the
surrounding.
Endothermic
It feels:
Cold
Exothermic
It feels:
Hot
Endothermic
Exothermic
Examples:
Examples:
• Cooking an egg
• Baking a bread
• Candle flame
• Rusting Iron
Exothermic
Reaction
Endothermic
Reaction
Heat (Thermal Energy) in phase
change is not the same as Heat of
Reaction.
Phase Change = Physical Change
Chemical Reaction = Chemical
Change
Example
Non-Example
• Cooking Egg
• Heat of
• Baking of cake
melting
• Activation of
• Heat of
cold pack
vaporization
• Heat of
sublimation
Example
• Candle
burning
• Explosion of
dynamite
• Activation of
yeast
Non-Example
• Heat of
deposition
• Heat of
freezing
• Heat of
condensation
6 March 2013
In your own understanding, what causes
steel to rust. Explain your answer in 2-3
sentences.


Minimum amount of energy needed to start a
chemical reaction
All reactions require a certain amount of
activation energy.
 Surface
Area
 Temperature
 Concentration
 Presence of catalyst or
inhibitor
Factors
Surface Area
Effects
The greater the area exposed, speed
up the reaction. Speeding up reactions
are both useful and harmful.
Useful: chewing food to make it easy to
digest.
Harmful: gas fumes or dust particles
ignites easily.
Temperature
Increasing the temperature,
increases the movement of the
particles and energy.
Decreasing the temperature,
decreases the movement of the
particles and energy.
Something good to remember:
We store food in the refrigerator
to lower the temperature and
slowdown the reaction in spoiling
food.
Concentration
It is the amount of stuff(substance)
in a given volume.
Example:
• Adding more sugar in coffee
increases the concentration of
sugar (sweeter).
• Adding more lemon juice in
lemonade increases the
concentration of acidity
(sourness).
Catalyst
A material added to reduce the
activation energy.
Example: Lead and Sulfur as fuel
additive
Enzymes are examples of catalyst
found in the human body.
Inhibitors
A material added to reduce the rate
of reaction.
Examples:
• Food preservatives
• Lubricant/protective coating


Is popping popcorn a physical change or a
chemical change? Explain your answer.
Due: March 01, 2013
 Objective:
◦ Observe a chemical reaction.
◦ Observe an endothermic
reaction.
1.3 grams citric acid (H3C6H5O7)
 1.5 grams Baking Soda = Sodium
Bicarbonate (NaHCO3)
 Zip-lock bag
 Small cup
 Electronic scale
 Graduated cylinder
 Weighing plate
 20 mL H2O

H3C6H5O7 + 3NaHCO3
Citric acid
+ sodium
bicarbonate
CO2 + 3H2O + NaC6H5O7
carbon + water + sodium citrate
dioxide

Procedure:
◦ Place weighing plat on scale – press “zero” so that scale doesn’t
measure the mass of the weighing plate.
◦ Measure 1.5g sodium bicarbonate (baking soda) onto the plate.
Add to plastic bag.
◦ Measure 1.3g citric acid onto plate. Add to plastic bag.
◦ Using the graduated cylinder, measure 20 mL of H2O. Pour the
water into the small cup.
◦ Place the cup inside the plastic bag standing up. Be careful not
to spill the water!
◦ Carefully squeeze the air out of the bag and zip the bag tightly
shut.
◦ Tip the cup over to spill the water and mix ingredients with your
hands.
◦ Record your observations below in the data section.
◦ Clean your lab station and answer discussion questions below.
Reactants
Citric Acid
Sodium
Bicarbonate
Elements in
Reactant
Observations
What do you SEE
happening during the
reaction?
What do you FEEL
happening during the
reaction?
1.
2.
3.
4.
5.
Do you think this was a physical or chemical
reaction? What is your evidence?
What do you think was produced in this reaction?
What is your evidence?
From what you observed and felt during the
reaction do you think energy was going into the
reaction (being used up) or out of the reaction
(heat is being produced)? What is your evidence?
From what you observed in today’s lab, what do
you think an endothermic reaction is?
What is one question you have about this
experiment? (write AT LEAST 1 question)
 Objective:
◦Observe a chemical reaction.
◦Observe an exothermic
reaction.
 Materials:







1.5 grams yeast
20 mL hydrogen peroxide (H2O2)
Zip-lock bag
Small cup
Electronic scale
Graduated cylinder
Weighing plate
Procedures
1. Place weighing plat on scale – press “zero” so that scale doesn’t
measure the mass of the weighing plate.
2. Measure 1.5g yeast onto the plate. Add to plastic bag.
3. Using the graduated cylinder, measure 20 mL of H2O2. Pour the
hydrogen peroxide into the small cup.
4. Place the cup inside the plastic bag standing up. Be careful not
to spill!
5. Carefully squeeze the air out of the bag and zip the bag tightly
shut.
6. Tip the cup over to spill the hydrogen peroxide and mix
ingredients with your hands.
7. Record your observations below in the data section.
8. Clean your lab station and answer discussion questions below.
Reactants
Elements in
Reactant
Hydrogen
Peroxide
Yeast
(this is a type
of cell and
has LOTS of
elements)
Observations
What do you SEE
happening during the
reaction?
What do you FEEL
happening during the
reaction?
1.
Do you think this was a physical or chemical reaction? What is your
evidence?
2.
What do you think was produced in this reaction? What is your
evidence?
3.
From what you observed and felt during the reaction do you think
energy was going into the reaction (being used up) or out of the
reaction (heat is being produced)? What is your evidence?
4.
From what you observed in today’s lab, what do you think an
exothermic reaction is?
5.
What is one question you have about this experiment? (write AT
LEAST 1 question)



How can you tell if a chemical reaction is
endothermic or exothermic?
What are common daily events involving
endothermic or exothermic reactions? Name
at least 2 examples per type, then support
your answer by paraphrasing the concepts
you learned?
Why are reactions (exothermic and
endothermic) important to our existence?
 Sugar
in tea
dissolving
•Chemical Change
•Physical Change
 Logs
burning
•Chemical Change
•Physical Change

Breaking water up by
separating it into hydrogen
and oxygen
•Chemical Change
•Physical Change
 Cutting
paper
•Chemical Change
•Physical Change
 Crushing
aspirin
an
•Chemical Change
•Physical Change
 Metal
rusting
•Chemical Change
•Physical Change
 An
egg rotting
•Chemical Change
•Physical Change
 An
egg breaking
•Chemical Change
•Physical Change