G10 Science Q4- Week 5-6- Conservation of Chemical Reaction..ppt

science 10

1. Chemical
Reaction
PREPARED BY: TYPE YOUR NAME HERE

2. S10MT - IVe - g -23
Apply the principles
of conservation of
mass to chemical
reactions

3. Chemical Reactions
Result in one or more new
substances being formed from one
or more original substances

4. Chemical Reaction Indicators
Formation of a gas
Emission of light or heat
Formation of a precipitate
Color change

5. Chemical Reactions
Reactants:
the substances that undergo change
What you start with
Products:
the new substances formed
What you end up with
Reactants change to Products
Carbon + Oxygen change to Carbon dioxide

6. Reactants
Products

7. Chemical Energy Chemical Energy
The chemical energy of a substance is the sum
of its potential energy (stored energy) and
kinetic energy (energy of movement). These
energies result from such things as:
◦Attractions between electrons and protons
◦Repulsions between nuclei
◦Repulsions between electrons
◦Movement of electrons
◦Vibrations of and rotations around bonds

8. All chemical reactions result in a change in
the chemical energy of the reactants as
they form the products
Reaction Energy

9. Reaction EnergyReaction Energy
During a chemical reaction, the
atoms in the reactants are
arranged into products with
different amounts of chemical
energies.

10. Reaction Energy
•Chemical changes that give
off energy are called
exothermic reactions.
Chemical changes that
absorb energy are
called endothermic
reactions.

11. Exothermic Exothermic
The total chemical energy of the products is less than the energy of the reactants.
the difference in energy is released into the environment, often as heat energy.

12. Exothermic Reactions
25
o
C 45
o
C
Gets hot
Hydrochloric
acid
magnesium
Magnesium + Hydrochloric acid

13. Energy Level Diagram: Exothermic Reaction
E
n
e
r
g
y

/

k
J
)
Progress of reaction (time)
reactants
Reactants have more chemical
energy.
Some of this is lost as heat
which spreads out into the
room.
products
Products now have less
chemical energy than
reactants.

14. Endothermic Endothermic
The chemical energy of the products is greater than the energy of the reactants.
Energy must be absorbed from the surrounds in order for the reaction to occur.

15. Endothermic Reactions
Ammonium
nitrate
Water
Cools
Heat
energy
taken
in as the
mixture
returns
back to
room
temp.

16. products
E
n
e
r
g
y

/

k
J
)
Progress of reaction
reactants
H
This is how
much energy
is taken in
Energy Level Diagram: Endothermic Process

17. Reaction EnergyReaction Energy
Why doesn’t natural gas burst immediately
into flame when it comes into contact with
air?
Why must matches be struck for them to
light?
To answer these questions you need to think
about what happens to the chemical bonds of
the substances during a reaction.

18. Reaction EnergyReaction Energy
The bonds between the atoms in the reactants must first be
broken.
For this to occur energy must always be absorbed
New bonds form as the products are created
Energy is always released as this happens

19. Reaction Energy
Step 1: Energy must be SUPPLIED
to break bonds:
Step 2: Energy is RELEASED when new
bonds are made:
A reaction is EXOTHERMIC if more energy is RELEASED then SUPPLIED. If
more energy is SUPPLIED then is RELEASED then the reaction is
ENDOTHERMIC

20. Burning Methane
CH
4
+ 2O
2
2H
2
O + CO
2
These bonds
must be
broken
:These
bonds
must
form

21. Activation EnergyActivation Energy
The energy required to break the bonds of reactants is called the activation
energy.
A diagram showing this is called an energy profile.

22. Why is Switzerland like a chemical reaction?

23. Activation Energy
Chemical Reactions must go over an energy hill like a car over
the mountains (Swiss Alps).

24. Homework
Read 7.3

25. Collision TheoryCollision Theory
For a chemical reaction to occur, the particles involved must
collide with each other.
The collisions must be with sufficient energy to overcome the
activation energy ‘barrier’.
The rate of reaction (how quickly the reaction occurs)
depends on the number of energy sufficient collisions per
time.

26. Collision Model
Molecules must collide in order for a reaction to
occur.
What factors affect the rate of collisions?

27. Factors That Affect Reaction Factors That Affect Reaction
RatesRates
There are four main ways in which reaction rates can be
increases:
–Increase the surface area of solid reactants (crush)
–Increase the concentration of the reactants
–Increasing the temperature of the reactants
–Adding a catalyst
Explain how each of these factors can increase the rate of
reaction.

28. Surface Area
•Only the reactants that are on the surface of a cube are
able to react. They are the only molecules exposed to
other reactants. The greater the number of exposed
molecules the larger the number of possible collisions.
•Take a cube 2 X 2 X 2 cm. Find the total surface area.
•Brake the cube into 8 separate cubes of 1 X 1 X 1 cm.
Find the total surface area.

29. Concentration
As the concentration of the reactants goes up the
distance between the molecules becomes less.
With less distance to travel the time between
collisions becomes less

30. Temperature
The faster the molecules move the less
time it take for them to reach another
molecule

31. CatalystCatalyst

32. Physical Equilibrium
•A dynamic state where the concentrations of all
reactants and products remain constant.

33. Physical Equilibrium
•You can change the equilibrium point by changing the
physical conditions.
–Take the top off a soda bottle. What happens to the
dissolved carbon dioxide?

34. Chemical Equilibrium
In chemical equilibrium, the
products break back down into the
reactants. The forward and
reverse reactions occur at the
same rate; the concentration of the
reactants and products remain
constant. You can cause the
equilibrium to shift by changing the
conditions such as temperature,
pressure and concentration

35. Describing Chemical Reactions
In a sentence
Copper reacts with chlorine to form copper
(I) chloride.
In a word equation
Copper + chlorine  copper (I) chloride
In a symbol equation
Cu
(s)
+ Cl
2(g)
 CuCl
(aq)

36. The seventeenth century French chemist Antoine Lavoisier
performed experiments that indicated conservation of mass in
chemical reactions.
Lavoisier's experiments suggested that when tin is heated,
the white powder formed results from the tin combining with a
gas from the air. The increase in mass of the powder over the
tin was the mass of the gas.
Lavoisier revolutionized chemistry by basing his ideas on
accurate measurements.
Antoine
Lavoisier
(1743-1794)

37. The English chemist Joseph Priestley discovered a gas that Lavoisier
later named oxygen
When oxygen combines
chemically with another
substance, the process
is called oxidation, and
the substance is said to
be oxidized.
Joseph Priestley
(1733-1804)

38. Describing Chemical Reactions
In a sentence
Copper reacts with chlorine to form copper
(I) chloride.
In a word equation
Copper + chlorine  copper (I) chloride
In a symbol equation
Cu
(s)
+ Cl
2(g)
 CuCl
(aq)
In a balanced symbol equation
2Cu
(s)
+ Cl
2(g)
 2CuCl
(aq)

39. Diatomic elements
There are 8 elements that never want to
be alone. They form diatomic molecules.
H
2
, N
2
, O
2
, F
2
, Cl
2
, Br
2
, I
2
, and At
2

The –gens and the –ines
1 + 7 pattern on the periodic table

41. Balancing EquationsBalancing Equations
___ H___ H
22(g) + ___ O(g) + ___ O
22(g) ---> ___ H(g) ---> ___ H
22O(l)O(l)2 2
•What Happened to the Other Oxygen Atom?
•This equation is not balanced!
•Two hydrogen atoms from a hydrogen molecule (H
2)
combines with one of the oxygen atoms from an oxygen
molecule (O
2) to form H
2O. Then, the remaining oxygen atom
combines with two more hydrogen atoms (from another H
2
molecule) to make a second H
2O molecule.

42. Balancing Site
Practice Game
http://phet.colorado.edu/en/
simulation/balancing-chemical-
equations
Homework Checker
http://www.webqc.org/
balance.php

43. Convert this sentence to a balanced
symbol equation
Solid iron (III) sulfide reacts with hydrogen chloride to form iron (III)
chloride and hydrogen sulfide.
Fe
2S
3 + HCl  FeCl
3 + H
2S

44. Grouping Reactions (Types)
1.Synthesis or Composition Reactions
2.Decomposition Reactions
3.Single Replacement Reactions
4.Double Replacement reactions
5.Combustion reactions
You need to be able to identify and work with each type.

45. 1. Synthesis
C + O
2  CO
2
OO C+  O O C
A + B  AB

46. 2. Decomposition
NaCl  Na + Cl
2
AB  A + B
Cl Na Cl+ Na
Cl

47. 3. Single Replacement
CuCl
2 + Zn  ZnCl
2 + Cu
 Zn
ClCl
Cu
+
AB + C  CB + A
ClCl
Zn
Cu+

48. Single Replacement
Just because you can write a chemical equation does
not mean it will actually occur.
The element metal will replace the compound metal
only if it is more “active”
An Activity Series shows the metals arranged according
to their ability to undergo reactions
If the element metal is above the compound metal it
will replace

49. 4. Double Replacement
MgO + CaS  MgS + CaO
AB + CD  AD + CB
SO

Mg Ca
+
O
S
Mg Ca
+

50. 5. Combustion
CH
4
+ 2O
2
 CO
2
+ 2H
2
O
H
O
 C+
O
C
+
H
H
H
O
O
H
O
H
C + AB  AC + BC
OO
O
H
H

51. Summary
An equation:
Describes a reaction
Must be balanced to follow The Law of
Conservation of Matter
Can only be balanced by changing the
coefficients.
Can describe different types of reactions.

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