Chapter 4.1
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Transcript of Chapter 4.1
Chemical Reactions
Chemical Change– the rearrangement of the atoms in a substance that creates new products with different chemical properties
Chemical Reaction-- the process in which one or more substances undergo a chemical change Change in energy Energy can be released (heat,
light, sound) or absorbed Occur at different rates: a reaction can be slow or fast
(a catalyst is used to speed up reactions)
Demos
Q: How do we know a chemical change has occurred?
Observe:
Demo 1– lead nitrate + potassium iodide
Demo 2– baking soda + citric acid solution
Clues to a Chemical Reaction
Change in colourPrecipitate formsEnergy is released or absorbed Gas is producedDifficult to reverse
REMEMBER: A change in state or dissolving a substance is a physical change-- NOT a chemical change
How can we speed up a chemical reaction?
Increase the temperature
Increase the surface area
Increase reactant concentration
CATALYST: A substance that makes a chemical reaction go faster WITHOUT being consumed.
Chemical Equations
Using words or symbols and formulas to represent a chemical reaction
Starting materials= “reactants”New substances= “products”An arrow is read as “produces”States of matter are in brackets
(s)= solid (l)= liquid (g)= gas (aq)= dissolved in water
REACTANTS PRODUCTS
Word Equations
Words represent the chemical reaction
REMEMBER: any compound that is not molecular, check the criss cross rule first.
Example:
Lithium + Aluminum Chloride Aluminum + Lithium Chloride
Skeleton Equations
An unbalanced equation that represents the chemical formulas of reactants and products
Ex. Na + O2 Na2O
Rules:Write the symbol of a metal NOT in a compoundIf the non-metal is part of hockey stick and puck,
write it as a diatomic molecule (H2, N2, O2, F2, Cl2, Br2, I2)
Write the formula of other compounds using rules you have learned
Law of Conservation of Mass
In a chemical reaction…
The total mass of reactants EQUALS the total mass of products because elements cannot be created nor destroyed in a chemical reaction. They can only be rearranged!
Formula Equations
Formulas represent reactions Include states of matterCoefficients show how the ratios of different
substances in the chemical reaction
Ex. 2 N2 (g) + 5 O2 (g) 2 N2O5 (s)
Balancing Chemical Formulas
Some tips:
Balance polyatomic ions first if the same ion is on both sides of the equations
Balance all other elements other than H and O
Balance HBalance O
Examples
1. FeCl3 + NaOH Fe(OH)3 + NaCl
2. Cu + AgNO3 Cu(NO3)2 + Ag
3. C5H12 + O2 CO2 + H2O
4. C2H6 + O2 CO2 + H2O
Some Helpful Videos
Elephant toothpaste (catalyst example): http://www.youtube.com/watch?v=4N0m95PExHY
Balancing chemical equations: http://www.youtube.com/watch?v=HB6cG7bQew0
Practice balancing chemical equations:http://www.sky-web.net/science/balancing_chemical_equations_examples.htm