Post on 21-Dec-2015
transcript
8th Grade Science
Adapted by T. Trimpe http://sciencespot.net/
http://www.unit5.org/chemistry/Equations.html
Remember: Chemical Changes
• Chemical change: a change that occurs causing the identity of the substance to change– Burning paper– Digesting food – Electrolysis of water
• A chemical change is called a chemical reaction
Remember: Chemical Reaction• Chemical reaction: occurs when the
original substance changes form into a new substance. Some clues to a chemical reaction may include bubbles, smoke, a strong smell, color change, temperature change, or a sizzling sound
Chemical Changes Cont’d• Indicators of a chemical change:
• Evolution of light
• Evolution of heat
• Evolution of a gas
• Color change
• Formation of a precipitate
Chemical Equations
• Depict the kind of reactantsreactants and productsproducts
• and their relative amounts in a reaction.
• 4 Al(s) + 3 O2(g) 2 Al2O3(s)
• The letters (s), (g), and (l) are the
• physical states of compounds
Chemical Equations
• Reactants – the substances that exist before a chemical change (or reaction) takes place.
• Products – the new substance(s) that are formed during the chemical changes.
• CHEMICAL EQUATION indicates the reactants and products of a reaction.
REACTANTS PRODUCTS
Chemical Equations
The number in the front is called a coefficientoefficient. . It tells you how many molecules in a reaction.• coefficient
•4 Al(s) + 3 O2(g) 2 Al2O3(s)
• subscript
•The number to the right of the symbols is called a subscript. It tells you how many of the same atom.
Chemical Equations
• When a coefficient is in front of a molecule and a subscript for an atom, you will multiply both numbers in order to determine the number of atoms that will be involved in the chemical reaction.
2 Al2O3
Al = 4 O = 6
Type of Reaction
Definition Equation
Synthesis
Decomposition
Single Replacement
Double Replacement
Watch the movie and then complete the chart.
A = Red B = Blue C = Green D = Yellow
A + B → AB
AB → A + B
AB + C → AC + B
AB + CD → AC + BD
Two or more elements or compounds combine to make a more complex
substance
Compounds break down into simpler substances
Occurs when one element replaces another one in a
compound
Occurs when different atoms in two different
compounds trade places
Identifying Chemical Reactions
____ P + O2 → P4O10 ____ Mg + O2 → MgO
____ HgO → Hg + O2 ____ Al2O3 → Al + O2
____ Cl2 + NaBr → NaCl + Br2 ____ H2 + N2 → NH3
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