UNIT 4:
CHEMICAL REACTIONS & SPECIAL
TOPICS
BILL NYE THE SCIENCE GUY
 http://www.youtube.com/watch?v=PlwuxpMh8nk
7.1: DESCRIBING REACTIONS
The most useful way of describing reactions (or a

chemical change) is by stating what was pres...
CHEMICAL CHANGE
 chemical reaction
 process in which one or more substances are changed into new

substances

 reactant...
CONSERVATION OF MASS
The French chemist Antoine Lavoisier

established that the total mass of the products
always equals ...
WRITING EQUATIONS
chemical equation
shorthand method to describe a chemical

reaction using chemical formulas and
other ...
WRITING EQUATIONS
(aq) – aqueous (substance dissolved in water)
(s)– solid
(l) – liquid
(g) – gas
coefficients – the numbe...
BALANCING EQUATIONS
 If you notice that the number of atoms on the left side does

not equal the number of atoms on the r...
BALANCING EQUATION RULES
1. You should NEVER change the subscripts in a

formula.
2. Start by, counting the number of atom...
EXAMPLE
 Balance the following equation

NiCl2(aq) + NaOH(aq)  Ni(OH)2(s) + NaCl(aq)
EXAMPLE

HgO(s)  Hg(l) + O2(g)
7.2: TYPES OF REACTIONS
 Reactions

are classified by the type of reactant or
the number of reactants and products.
Ther...
SYNTHESIS
A synthesis reaction is a reaction in which two or

more substances react to form a single substance.
 The pro...
DECOMPOSITION
 The opposite of synthesis

A decomposition reaction is a reaction in which a

compound breaks down into t...
SINGLE REPLACEMENT
A single replacement reaction is a reaction in

which one element takes the place of another
element i...
DOUBLE REPLACEMENT
A double replacement reaction is one in which

two different compounds exchange positive ions
and form...
7.3: ENERGY CHANGES IN REACTIONS
Chemical Energy – the energy stored in the

chemical bonds of a substance.

Chemical Re...
BREAKING BONDS
Breaking Bonds REQUIRES energy.
 This means we need to ADD energy in order to break

the bonds of reactin...
FORMING BONDS
The formation of chemical bonds RELEASES

energy.
 When new chemical bonds are formed, a bit of energy is
...
ENERGY IN REACTIONS
During a chemical reaction, energy is either

ABSORBED or RELEASED.
 We describe these reactions in ...
EXOTHERMIC REACTIONS
A chemical reaction that RELEASES energy is called

an exothermic reaction.
 The energy released as...
ENDOTHERMIC REACTIONS
A chemical reaction that absorbs energy from its

surroundings is called an endothermic reaction.
...
CONSERVATION OF ENERGY
The total amount of energy BEFORE a reaction is

EQUAL to the total amount of energy AFTER a
react...
8.1: FORMATION OF SOLUTIONS
A solution is a mixture that forms when

substances dissolve and form a homogeneous
mixture
...
DISSOLVING
Every solution has two components
 A solute is a substance who particles are dissolved in a

solution
 A sol...
DISSOCIATION
 In order for a solution to form, the attractions that hold the solute

together and the solvent together mu...
DISPERSION
Sugar dissolves into water by dispersion, or

breaking into small pieces that spread throughout
the water.
 E...
IONIZATION
The process in which molecules gain or lose

electrons is known as ionization.
 Example: Ions are formed by t...
PROPERTIES OF LIQUID SOLUTIONS
Conductivity: ability to conduct electric current
Boiling Point: temperature needed for s...
8.2: SOLUBILITY & CONCENTRATION
The maximum amount of solute that dissolves in a

given amount of solvent at a constant t...
SATURATED
A saturated solution is one that contains as much

solute as the solvent can hold at a given
temperature.
UNSATURATED
A solution that has less than the maximum amount

of solute that can be dissolved is called an
unsaturated so...
SUPERSATURATED
A supersaturated solution is one that contains

more solute than it can normally hold at a given
temperatu...
FACTORS AFFECTING SOLUBILITY
Polarity of the solvent
 “like dissolves like”
 Solution formation is more likely to happe...
CONCENTRATION
The concentration of a solution is the amount

solute dissolved in a specified amount of solution.
 Can be...
SOLUBILITY CURVE
 Each line on the graph is

called a solubility curve for a
particular substance.
 You can use a solubi...
10.1: RADIOACTIVITY
Henri Becquerel
 1896
 left uranium salt in a drawer with a photographic
plate
 when he developed ...
THEY DISCOVERED …
 Radiation
 release of matter and energy from nucleus

 Light energy (electromagnetic spectrum)
 all...
STRONG FORCES
Protons are held together by strong

forces
short range force
as the distance increases, the force weaken...
STRONG FORCES
 to hold a nucleus together tightly, the

nucleus can decay and give off matter and
energy
 stable nucleus...
RADIOACTIVE ELEMENTS
 radioactivity
 the process of nuclear decay

 elements after #83 are radioactive
 all elements a...
REVIEW !!!!!!!
 Mass number = # protons + # neutrons

 Atomic number = # of protons

Example

(12 = mass #)
(6= atomic #...
REVIEW: ISOTOPES
 most elements have at least one radioactive

isotope
 isotope
 same element with a different number o...
RADIOACTIVE DECAY
Transmutation
 the process of changing one element into another through

nuclear decay

Radioactive d...
ALPHA DECAY
alpha decay (α)
 releases alpha particle (a helium nucleus)
 a helium nucleus consists of 2 protons and 2 n...
BETA DECAY
Beta Decay (β)
 release beta particle it occurs when a neutron breaks down

into 1 electron and 1 proton

th...
PRACTICE: ALPHA & BETA DECAY
214
84

222
86

214
82

234
92

Po
Rn
Pb
U

210
82

Pb ______

______

4
2

______

0
1

234
...
NUCLEAR REACTIONS
 FISSION
 process of splitting a nucleus into several smaller nuclei
NUCLEAR REACTIONS
FUSION:
 Two nuclei with low masses are combined to form one

nucleus of larger mass
HALF LIFE
half-life
 the amount of time it takes for
half the nuclei in a sample of the
isotope to decay
the nucleus le...
EXAMPLE: HALF LIFE
 Assume a 20g sample of Ba-139 has a

half-life of 86 minutes.

how much Ba-139 remains after 86 minut...
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Physical Science Unit 4

  1. 1. UNIT 4: CHEMICAL REACTIONS & SPECIAL TOPICS
  2. 2. BILL NYE THE SCIENCE GUY  http://www.youtube.com/watch?v=PlwuxpMh8nk
  3. 3. 7.1: DESCRIBING REACTIONS The most useful way of describing reactions (or a chemical change) is by stating what was present before and after the chemical change.
  4. 4. CHEMICAL CHANGE  chemical reaction  process in which one or more substances are changed into new substances  reactants  substance that reacts  product the new substance that is formed
  5. 5. CONSERVATION OF MASS The French chemist Antoine Lavoisier established that the total mass of the products always equals the total mass of the reactants.  This is called the Law of Conservation of Mass (mass is not created nor destroyed in a chemical reaction).
  6. 6. WRITING EQUATIONS chemical equation shorthand method to describe a chemical reaction using chemical formulas and other symbols Reactants HgO(s)  Products Hg(l) + O2(g)
  7. 7. WRITING EQUATIONS (aq) – aqueous (substance dissolved in water) (s)– solid (l) – liquid (g) – gas coefficients – the numbers to the left of the formulas used to help balance the equation
  8. 8. BALANCING EQUATIONS  If you notice that the number of atoms on the left side does not equal the number of atoms on the right side then we must balance the equation.  Since mass is conserved before and after a chemical reaction, an equation MUST BE balanced in order for it to be true.
  9. 9. BALANCING EQUATION RULES 1. You should NEVER change the subscripts in a formula. 2. Start by, counting the number of atoms of each element on each side of the equation. 3. Change one or more coefficients until the equation is balanced
  10. 10. EXAMPLE  Balance the following equation NiCl2(aq) + NaOH(aq)  Ni(OH)2(s) + NaCl(aq)
  11. 11. EXAMPLE HgO(s)  Hg(l) + O2(g)
  12. 12. 7.2: TYPES OF REACTIONS  Reactions are classified by the type of reactant or the number of reactants and products. There are 4 different types of reactions that we will discuss  Synthesis  Decomposition  Single-Replacement  Double-Replacement
  13. 13. SYNTHESIS A synthesis reaction is a reaction in which two or more substances react to form a single substance.  The product synthesized is always a compound  Examples A + B  AB 2Na + Cl2 2NaCl
  14. 14. DECOMPOSITION  The opposite of synthesis A decomposition reaction is a reaction in which a compound breaks down into two or more simpler substances.  The reactant MUST BE a compound.  Examples AB A + B 2H2O 2H2 + O2
  15. 15. SINGLE REPLACEMENT A single replacement reaction is a reaction in which one element takes the place of another element in a compound. Example Form: A + BC B + AC Cu + 2AgNO3  2Ag + Cu(NO3)2
  16. 16. DOUBLE REPLACEMENT A double replacement reaction is one in which two different compounds exchange positive ions and form two new compounds. Example Forms: AB + CD AD + CB Pb(NO3)2 + 2KI PbI2 + 2KNO3
  17. 17. 7.3: ENERGY CHANGES IN REACTIONS Chemical Energy – the energy stored in the chemical bonds of a substance. Chemical Reactions involve the breaking of chemical bonds in the reactants and the formation of chemical bonds in the products.
  18. 18. BREAKING BONDS Breaking Bonds REQUIRES energy.  This means we need to ADD energy in order to break the bonds of reacting molecules in order to get the reaction started.
  19. 19. FORMING BONDS The formation of chemical bonds RELEASES energy.  When new chemical bonds are formed, a bit of energy is released usually in the form of heat or light.
  20. 20. ENERGY IN REACTIONS During a chemical reaction, energy is either ABSORBED or RELEASED.  We describe these reactions in two different ways either Exothermic or Endothermic.
  21. 21. EXOTHERMIC REACTIONS A chemical reaction that RELEASES energy is called an exothermic reaction.  The energy released as the products form is greater than the energy required to break the bonds in the reactants.  Think of it as energy is EXITING the reaction  EXiting _ Exothermic
  22. 22. ENDOTHERMIC REACTIONS A chemical reaction that absorbs energy from its surroundings is called an endothermic reaction.  This means that there is more energy require to break the bonds of the reactants than is released by the formation of the products.
  23. 23. CONSERVATION OF ENERGY The total amount of energy BEFORE a reaction is EQUAL to the total amount of energy AFTER a reaction.  This is called the Conservation of Energy.
  24. 24. 8.1: FORMATION OF SOLUTIONS A solution is a mixture that forms when substances dissolve and form a homogeneous mixture  In order for a solution to form, one substance must dissolve in another.
  25. 25. DISSOLVING Every solution has two components  A solute is a substance who particles are dissolved in a solution  A solvent is the substance in which the solute dissolves in. There are three ways that substances can dissolve into water: dissociation, dispersion, ionization
  26. 26. DISSOCIATION  In order for a solution to form, the attractions that hold the solute together and the solvent together must be overcome. The process in which an ionic compound separates into ions as it dissolves is called dissociation.  Example: Sodium Chloride & Water
  27. 27. DISPERSION Sugar dissolves into water by dispersion, or breaking into small pieces that spread throughout the water.  Example: Sugar & Water
  28. 28. IONIZATION The process in which molecules gain or lose electrons is known as ionization.  Example: Ions are formed by the reaction of the solute and solvent particles.
  29. 29. PROPERTIES OF LIQUID SOLUTIONS Conductivity: ability to conduct electric current Boiling Point: temperature needed for solution to change from liquid phase to gas phase Freezing Point: temperature needed for solution to turn from liquid phase to solid phase. Solutions can also be described as endothermic or exothermic depending upon whether energy is released or absorbed.
  30. 30. 8.2: SOLUBILITY & CONCENTRATION The maximum amount of solute that dissolves in a given amount of solvent at a constant temperature is. called solubility  Depending upon the amount of solute in a solution, solutions can be described as either saturated, unsaturated or supersaturated.
  31. 31. SATURATED A saturated solution is one that contains as much solute as the solvent can hold at a given temperature.
  32. 32. UNSATURATED A solution that has less than the maximum amount of solute that can be dissolved is called an unsaturated solution.
  33. 33. SUPERSATURATED A supersaturated solution is one that contains more solute than it can normally hold at a given temperature.  Usually very unstable.
  34. 34. FACTORS AFFECTING SOLUBILITY Polarity of the solvent  “like dissolves like”  Solution formation is more likely to happen when the solute and solvent are either both polar or both nonpolar. Temperature  The solubility of a solids increases as the solvent temperature increases Pressure  Increasing pressure on a gas increases solubility in a liquid.
  35. 35. CONCENTRATION The concentration of a solution is the amount solute dissolved in a specified amount of solution.  Can be expressed as percent by volume, percent by mass and molarity.
  36. 36. SOLUBILITY CURVE  Each line on the graph is called a solubility curve for a particular substance.  You can use a solubility curve to figure out how much solute will dissolve at any temperature given on the graph.
  37. 37. 10.1: RADIOACTIVITY Henri Becquerel  1896  left uranium salt in a drawer with a photographic plate  when he developed the plate, he found an outline of the clumps of the uranium salt  he hypothesized that the uranium salt emitted some sort of energy Marie and Pierre Curie  students of Becquerel  2 years later, they discovered Po and Ra while studying uranium ore “pitch blende”
  38. 38. THEY DISCOVERED …  Radiation  release of matter and energy from nucleus  Light energy (electromagnetic spectrum)  all forms of radiation
  39. 39. STRONG FORCES Protons are held together by strong forces short range force as the distance increases, the force weakens causes protons and neutrons to be attracted to each other
  40. 40. STRONG FORCES  to hold a nucleus together tightly, the nucleus can decay and give off matter and energy  stable nucleus  stays together permanently  unstable nuclei  radioactive!!!!  nucleus does not stay together; emits matter and energy
  41. 41. RADIOACTIVE ELEMENTS  radioactivity  the process of nuclear decay  elements after #83 are radioactive  all elements after #92 are synthetic and decay soon after they are created
  42. 42. REVIEW !!!!!!!  Mass number = # protons + # neutrons  Atomic number = # of protons Example (12 = mass #) (6= atomic #) 12 6 C
  43. 43. REVIEW: ISOTOPES  most elements have at least one radioactive isotope  isotope  same element with a different number of neutrons  Example: Carbon-12 (stable) Carbon-14 (unstable)
  44. 44. RADIOACTIVE DECAY Transmutation  the process of changing one element into another through nuclear decay Radioactive decay  occurs until a stable nucleus is formed
  45. 45. ALPHA DECAY alpha decay (α)  releases alpha particle (a helium nucleus)  a helium nucleus consists of 2 protons and 2 neutrons  atomic mass is 4  atomic number is 2 4 2He  Ex: 238 92 U 234 90 Th + 4 2He
  46. 46. BETA DECAY Beta Decay (β)  release beta particle it occurs when a neutron breaks down into 1 electron and 1 proton the result is an atom with 1 more proton Ex: 14 6 C 14 7 N+ 0 e -1
  47. 47. PRACTICE: ALPHA & BETA DECAY 214 84 222 86 214 82 234 92 Po Rn Pb U 210 82 Pb ______ ______ 4 2 ______ 0 1 234 93 Np He e ______
  48. 48. NUCLEAR REACTIONS  FISSION  process of splitting a nucleus into several smaller nuclei
  49. 49. NUCLEAR REACTIONS FUSION:  Two nuclei with low masses are combined to form one nucleus of larger mass
  50. 50. HALF LIFE half-life  the amount of time it takes for half the nuclei in a sample of the isotope to decay the nucleus left after the isotope decays is called the daughter nucleus some half-lives are seconds, others are millions of years
  51. 51. EXAMPLE: HALF LIFE  Assume a 20g sample of Ba-139 has a half-life of 86 minutes. how much Ba-139 remains after 86 minutes?  after 172 minutes?  how many ½ lives leave 1.25g of Ba-139? 
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