8th Grade Science

1
Chemical and Nuclear Reactions

• 8th Grade Science
• T. Trimpe http//sciencespot.net/

2
Law of Conservation of Matter (Mass)

• Matter is neither created nor destroyed
• Matter is conserved in a chemical reaction.
• The number and type of atoms stay the same.

3
Watch the movie and then complete the chart.
Type of Reaction Definition ? Equation
Synthesis
Decomposition
Single Replacement
Double Replacement
Two or more elements or compounds combine to make
a more complex substance
A B ? AB
AB ? A B
Compounds break down into simpler substances
Occurs when one element replaces another one in a
compound
AB C ? AC B
AB CD ? AC BD
Occurs when different atoms in two different
compounds trade places
A Red B Blue C Green D Yellow
4
Identifying Chemical Reactions
2. Use colored pencils to circle the common atoms
or compounds in each equation to help you
determine the type of reaction it illustrates.
Use the code below to classify each reaction. S
Synthesis D Decomposition SR
Single Replacement DR Double Replacement  
____ P O2 ? P4O10 ____ Mg
O2 ? MgO ____ HgO ? Hg
O2 ____ Al2O3 ? Al O2 ____
Cl2 NaBr ? NaCl Br2 ____ H2
N2 ? NH3
5
____ Na Br2 ? NaBr ____ CuCl2
H2S ? CuS HCl   ____ HgO
Cl2 ? HgCl O2 ____ C H2 ?
CH4   ____ KClO3  ?   KCl    O2 
____ S8 F2 ? SF6   ____
BaCl2     Na2 SO4 ?     NaCl     BaSO4
6
Law of Conservation of Energy

• Just like the Law of Conservation of Matter,
  energy is also conserved in a chemical reaction.
• The reaction either gives off energy or absorbs
  energy.

7
Exothermic Endothermic Reactions

• Exothermic
• Occurs when breaking a bond
• ex decomposition reaction
• Releases energy
• Feels hot
• Endothermic
• Occurs when forming a bond
• ex synthesis reaction
• Absorbs energy
• Feels cold

8
Nuclear Reactions

• Take place in the nucleus of an atom.
• Fission when a nucleus is split
• Ex nuclear bomb, nuclear power plant
• Fusion when 2 nuclei are forced together
• Ex how the sun generates heat

9
Break Apart? or Smash Together?
10
Nuclear Reactions

• Nuclear decay radioactivity
• Ex getting sun-burned from UV rays
• Ex radio-carbon dating of old things