Download Reacting to Density

REACTING TO DENSITY
REACTING TO DENSITY – PART 1
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Conduct your experiment – follow your procedure
Make sure you include all data and observations!
Include sketches of each set-up AFTER the reaction.
Step 11 – See if the gas released will extinguish a
candle. Follow the procedure in your notebook! Make
sure you have a BEFORE and AFTER sketch.
Step 12 – Read and Take notes on important
vocabulary!
Step 12 a-d: Complete in your notebook
Step 13 – answer in your notebook.
Complete S&T #1-4 on page 84.
REACTING TO DENSITY PART 1
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P&P Step 7: Did the water bottle lose any
material during the reaction? How do you know?
REACTING TO DENSITY PART 1
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P&P Step 9: When you removed the cap (or
balloon), did any material exit the bottle? Did
this material have any mass? How do you know?
REACTING TO DENSITY PART 1
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P&P Step 10: Did the gas that was produced
extinguish a flame? What do you think the gas
was?
REACTING TO DENSITY PART 1
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12. Evidence For or Against a Chemical Reaction
What I observed
Evidence For or
Against chemical
Reaction
How I know
REACTING TO DENSITY PART 1
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13. Evidence For or Against Conservation of
Matter
What I observed
Evidence For or
Against
conservatoin of
matter
How I know
STOP & THINK P. 84
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1. The gas produced was carbon dioxide, the
same gas we exhale during breathing. Suppose
both the cap and balloon methods captured
exactly 50 molecules of carbon dioxide.
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A. Sketch these gas particles for both methods and
include highlight comments and captions.
STOP & THINK P. 84
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1A. Sketch these gas particles for both methods
and include highlight comments and captions.
STOP & THINK P. 84
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1b. Why should there be the same number of gas
particles in each bottle, provided the amount of
water and the size of the tablet were the same?
If the law of conservation of matter is true, then
the amount of gas produced must be the same if
the amounts of the reactants are the same.
STOP & THINK P. 84
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1c. Are the carbon dioxide particles moving or
stationary? How do you know?
The carbon dioxide particles must be moving,
otherwise the balloon would not inflate and stay
inflated. The only way the gas could generate a
pressure on the inside of the balloon is if those
gas particles on the inside were moving around
and colliding with the balloon walls to maintain
the pressure.
STOP & THINK P. 84
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1d. Illustrate your answer to 1c.
STOP & THINK P. 84
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2. In which method is the pressure inside the
bottle the greatest? What evidence supports your
answer?
The capped bottle has more pressure inside. If
you squeezed both bottles, you would have seen
that the capped bottle was more difficult to
squeeze.
STOP & THINK P. 84
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In which method is the density of the carbon
dioxide gas the greatest? What evidence
supports your answer?
The capped bottle has a greater gas
density. The mass is the same
(because the same number of particles
is produced), but the volume is less.
STOP & THINK P. 84
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What is the relationship between density and pressure
for a gas like carbon dioxide at a constant temperature?
(Note: place density on the vertical axis and pressure on
the horizontal axis.)
PART 2: CANDLE COMBUSTION
Read Introduction p. 85
 Combustion, or burning, is a chemical process in
which a substance reacts with oxygen to produce
heat and light.
 At the microscopic
level, atoms are being
rearranged to form
new products.
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PART 2: CANDLE COMBUSTION
How can we demonstrate that a candle burning
for 2 minutes represents a chemical reaction?
 Draw a sketch of the candle before and after, and
label your sketch with the words: solid, liquid,
gas, wick, flame, temperature change.
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PART 2: CANDLE COMBUSTION
Read P&P #3
 To help understand combustion at a microscopic
level, let's look at the combustion of methane.
 A methane molecule has 1 carbon atom (C) and 4
hydrogen atoms (H).
 It's chemical formula is CH4
 A chemical formula is a combination of symbols
and numbers that show which elements, and the
number of atoms of each element, that make up a
molecule of a compound. The numbers are called
subscripts.
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PART 2: CANDLE COMBUSTION
Chemical equations describe the chemical
reaction of elements and compounds to form new
compounds.
 The structure of a chemical equation is
reactants ------- products
 The arrow means “yields” and tells which
direction the reaction goes
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PART 2: CANDLE COMBUSTION
methane (CH4) and oxygen (O2) react to produce
water (H2O) and carbon dioxide (CO2).
 The equation looks like this:
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CH4 + O2
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CO2 + H2O
Does this equation violate the Law of
Conservation of Matter???
PART 2: CANDLE COMBUSTION
We need to balance the equation. Why?
 The number of atoms of each type must be equal
on both sides of the arrow. Why?
 You CANNOT change the chemical formula.
 You CANNOT add new products or reactants
 You CAN change the coefficients in front of the
existing reactants and products to make the
equation balance. (This is the same as adding
another molecule of a product or reactant.)
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PART 2: CANDLE COMBUSTION
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Let's balance this equation to show conservation
of matter...
CH4 + O2
CO2 + H2O
PART 3: PHASES OF MATTER
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Read Intro p. 87
PHYSICAL CHANGE
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A change where the composition of the substance
remains the same, even if the appearance does
not.
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Examples: changes of state: solid – liquid – gas
What is happening at the atomic level?
 Let’s look at a burning candle to find out…
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PART 3
What is required to
change candle wax
from the solid
phase to the liquid
phase?
 When a candle
burns, what is
happening
macroscopically?
 In which phase of
matter do particles
move about most
freely?
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PART 2&3: CANDLE COMBUSTION
Complete Stop & Think #1-4 p. 87
 Stop & Think #1-4 p. 89
 Reflect & Connect #1-4 p.89-90
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Does the law of
conservation of
matter apply to
physical changes
such as phase
changes?
S&T #1 P. 89
In which phase of matter does a CONSTANT
number of particles have a higher temp than its
other phases?
 How does increased temperature for a constant
number of particles affect density?
 Sketch the relationship between density and
temperature at a constant pressure and constant
number of particles.
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S&T #1
S&T #2
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In which phase of matter do attractions between
particles affect motion the most?
In which phase of matter do attractions between
particles affect motion least?
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This figure is a phase diagram. It shows how pressure
and temperature affect matter. Notice how the phase of
matter changes depending on temp. and pressure.