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Agenda Dec 7, 2016
Slip quiz 1
Some Chemical Reactions - using your notes from lab time
Teacher demonstrations and
Writing and Balancing Chemical Equations
Homework
Slip Quiz 1. Write out each question.
1. Equation for use when converting temperatures from
Celsius to Kelvin.
2. a) Equation for density b) Density of an object that
has a mass of 5.00g and a volume of 2.50mL.
3. Relationship between cm3 and mL for use when
working with volumes of liquids.
4. Prefix milli stands for?
5. Set up converting xmL to L using a conversion factor.
Slip Quiz 1.
1. Equation for use when converting temperatures from
Celsius to Kelvin.
K = ℃ + 273
Kelvin
Absolute temperature
Starts at Absolute zero 0K
Slip Quiz 1.
2. a) Equation for density b) Density of an
object that has a mass of 5.00g and a volume
of 2.50mL.
Density = mass
= 5.00g = 2.00 g/mL
volume
2.50mL
Slip Quiz 1.
3
3. Relationship between cm and mL for use
when working with volumes of liquids.
3
1 cm = 1 mL (page 27).
Just a handy relationship to remember.
Slip Quiz 1.
4. Prefix milli stands for? one thousandth (a
mL is a milliliter, one thousandth of a liter)
5. Set up converting xmL to L using a
conversion factor. 1L = 1000 mL so
x mL . 1L
= x L = 0.00x L
1000mL 1000
Chemical Reactions - typical pathway
Energy released by the
reaction system into the
surroundings = an
exothermic reaction
At which station did you observe
heat being released by the reaction
system?
You would have observed the outside of the
container feeling warmer during the reaction
than it was before the reaction started.
Blue station: Magnesium and
hydrochloric acid (dilute)
What else did we observe and do at this station?
Blue station: Magnesium and
hydrochloric acid (dilute)
Saw bubbles
Heard fizzing
Trapped the gas and then “popped” it with a
lighted splint - demonstrating that the gas being
given off was hydrogen
Magnesium all disappeared
New piece of paper
MLA heading
Chemical Equations
Word equation
Solid Magnesium reacts with dilute hydrochloric
acid to produce hydrogen gas and a solution
of...
Word equation
Solid Magnesium reacts with dilute hydrochloric
acid to produce hydrogen gas and a solution of
________________ (and heat).
Skeleton equation - translate the substances
that are matter into formula units or molecular
formulas, reactants on left of reaction arrow
Mg(s) + HCl(aq)
H2(g) + ? (aq)
Word equation
Solid Magnesium reacts with dilute hydrochloric
acid to produce hydrogen gas and a solution of
magnesium chloride (and heat).
Skeleton equation - translate the substances
that are matter into formula units or molecular
formulas, reactants on left of reaction arrow
Mg(s) + HCl(aq)
H2(g) + MgCl2(aq)
Skeleton equation - will not necessarily show
the correct relationship (ratio) between the
substances that are reacting and the products
that are made during the reaction.
Mg(s)
+ HCl(aq)
H2(g) + MgCl2 (aq)
Law of conservation of matter: Matter cannot
be created or destroyed during chemical
reactions.
Mg(s)
+ HCl(aq)
H2(g) + MgCl2 (aq)
A chemical equation should show us the
simplest ratio of materials that can react to form
the given products so that matter is conserved.
Mg(s) + HCl(aq)
H2(g) + MgCl2 (aq)
We need to take steps to find the simplest ratios
of these materials. - Step 1 - take an inventory
of individual atoms shown in skeleton
equation.
Step 1 - take an inventory of the atoms
Mg(s) + HCl(aq)
H2(g) + MgCl2 (aq)
1Mg
1Mg
1H
2H
1Cl
2Cl
Keep reactants on Left
Keep products on right
Mg(s)
1Mg
+ HCl(aq)
H2(g) + MgCl2 (aq)
1Mg
1H
2H
1Cl
2Cl
We have billions of atoms in our samples, we
only want the simplest ratio of each substance,
so we just need to think of factors that might
help us “balance” the relationships.
Mg(s)
1Mg
+ HCl(aq)
1H
1Cl
H2(g) + MgCl2 (aq)
1Mg
2H
2Cl
Step 2 - look for factors that will make it so that
no atoms are created or destroyed during the
reaction, (but are moved around like pieces of
Lego).
Mg(s)
1Mg
+ 2HCl(aq)
2H
2Cl
H2(g) + MgCl2 (aq)
1Mg
2H
2Cl
Step 3 - Write in the factor as a coefficient in
front of the relevant substance and, in this case,
BINGO! A balanced equation.
Cu(s) + HCl(aq)
No reaction
H2(g) + ?
product?
What did we react the hydrogen with to make
the pop we used to identify it?
What was the product of this new reaction?
Word Equation: Hydrogen gas reacts with
oxygen gas, if given a spark of energy, to
produce water vapor
Skeleton Equation:
H2(g) + O2(g)
H2O(g)
What do we do to avoid violating the law of
conservation of matter? (As written we’ve lost
an oxygen atom somewhere.)
Take inventory of atoms under Skeleton
Equation:
H2(g) + O2(g)
H2O(g)
2H
2O
2H
O
Remember we have billions of particles of each
substance in our samples - even a drop of water
H2(g) + O2(g)
H2O(g)
2H
2O
2H
O
Balanced Chemical equation:
2H2(g) + O2(g)
2H2O(g)
4H
2O
4H
2O
Now use what we know to predict the product
of this reaction and write a balanced equation
for the reaction:
Word Equation: Solid Magnesium reacts with
oxygen gas, if heated to get the reaction started,
to produce _____________ ?
Skeleton equation:
Mg(s) + O2(g)
?
Ionic or covalent compound?
Word Equation: Solid Magnesium reacts with
oxygen gas, if heated to get the reaction started,
to produce magnesium oxide (an ionic
compound, likely to be a solid).
Skeleton equation:
Mg(s) + O2(g)
MgO (s)
1 Mg
1Mg
2O
1O
Mg(s) + O2(g)
1 Mg
2O
MgO (s)
1Mg
1O
When we find factors that work - we call them
coefficients when writing chemical equations
Skeleton equation becomes balanced Eqaution:
2Mg(g) + O2(g)
2MgO (s)
2 Mg
2Mg
2O
2O
Demonstrate reaction to see if MgO is solid.
Write you observations in the space on the
Chemical Reactions worksheet
Magnesium has to be heated before it will start
to react with oxygen in the air, but once it starts
reacting it produces lots of heat and a bright
white light (another form of energy). When the
reaction is over a white powdery substance has
replaced the shiny, malleable metal. This white
powder is Magnesium oxide. Exothermic
reaction.
Solid copper reacts with oxygen when the
copper is heated to glowing red, a black
powdery oxide forms on the surface of the
metal (copper(II) oxide).
Cu(s) + O2(g)
CuO (s)
Solid copper reacts with oxygen when the
copper is heated to glowing read, a black
powdery oxide forms on the surface of the
metal (copper(II) oxide).
Skeleton Equation
Cu(g) + O2(g)
CuO (s)
1Cu
1Cu
2O
1O
Solid copper reacts with oxygen when the
copper is heated to glowing read, a black
powdery oxide forms on the surface of the
metal (copper(II) oxide).
Skeleton Equation becomes Balanced Equation
2Cu(s) + O2(g)
2CuO (s)
2Cu
2Cu
2O
2O
When we use a Bunsen Burner:
CH4 methane gas burns in oxygen producing
carbon dioxide gas, water vapor and giving out
lots of heat and light energy into the
surroundings. A very exothermic reaction.
Skeleton equation
CH4(g) + O2(g) →
CO2(g) + H2O(g)
Skeleton equation
CH4(g) + O2(g) →
1C
4H
2O
CO2(g) + H2O(g)
1C
2H
2O + 1O = 3O
Skeleton equation
CH4(g) +
O2(g) →
1C
4H
CO2(g) +
4H
2O + 2O = 4O
1C
2O
2H2O(g)
Skeleton equation becomes Balanced Equation
CH4(g) +
2O2(g) → CO2(g) + 2H2O(g)
1C
4H
4H
2O + 2O = 4O
1C
4O
Skeleton equation becomes Balanced Equation
CH4(g) +
2O2(g) → CO2(g) + 2H2O(g)
1C
4H
4H
2O + 2O = 4O
1C
4O
Hydrogen peroxide - decomposition reaction demonstration - predict products will be ...
Skeleton Equation:
H2O2(aq)
→ (g)
+ (l)
Hydrogen peroxide - decomposition reaction demonstration - predict products will be oxygen gas
(which supports combustion) and water.
Skeleton Equation:
H2O2(aq)
→ O2(g)
+ H2O(l)
Hydrogen peroxide - decomposition reaction demonstration - predict products will be oxygen gas
(which supports combustion) and water.
Skeleton Equation:
H2O2(aq)
→ O2(g)
+ H2O(l)
2H
2O
2O + 1O = 3O
2H
Hydrogen peroxide - decomposition reaction demonstration - predict products will be oxygen gas
(which supports combustion) and water.
Skeleton Equation becomes balanced equation:
2H2O2(aq)
4H
4O
→ O2(g)
+
2H2O(l)
2O + 2O = 4O
4H
Copper(II) carbonate - decomposition reaction demonstration - we predict products will be ...
Skeleton Equation:
CuCO3(s)
→ (g)
+ (s)
Copper carbonate - decomposition reaction demonstration - we predict products will be carbon
dioxide gas (which does not support combustion)
and copper (II) oxide.
Skeleton Equation is also balanced equation:
CuCO3(s)
1Cu
1C
3O
→ CO2(g)
1C
2O + O = 3O
+ CuO(s)
1Cu
Copper carbonate - decomposition reaction demonstration - we predict products will be carbon
dioxide gas (which does not support combustion)
and copper (II) oxide.
Skeleton Equation is also balanced equation:
Turn in your
CuCO3(s)
→ CO
(g)
+ CuO(s)
Chemical
Reactions
2
1Cu
1Cu
Observation Sheet
Now
1C
1C
3O
2O + O = 3O
Try balancing equations at home:
http://phet.colorado.edu/en/simulation/balancin
g-chemical-equations
Just be aware that when we write balanced
equations on paper, we don’t put 1 coefficients
(by writing a formula down, we are stating that
there is one of those molecules present ).