warm-up nov.7,2013 what are the clues that a chemical reaction has occurred? remember: write your...
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Warm-Up Nov.7,2013
What are the clues that a chemical reaction has occurred?
Remember: Write your name, block #, the date, the question, and your answer. Look to your notes if you can’t remember the format!!!
1. A gas bubbles off.
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2. A new solid material is formed (a precipitate.)
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3. Color change.
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4. Heat and/or light are emitted.
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Law of Conservation of Mass&
Balancing Chemical Equations
Objectives 8.P.1.4 Explain how the idea of atoms and a
balanced chemical equation support the law of
conservation of mass. Student Friendly Objective: I can use diagrams to model chemical
reactions. I can explain the Law of Conservation of
Mass. I can explain how chemical reactions are
represented so that mass is conserved. I can balance chemical equations and
explain why they are balanced
Vocabulary
Subscript Vs Coefficient Reactant Vs Product Atom Vs Molecule Law of Conservation of Mass Word Equation Skeleton Equation Balanced equation
Subscripts C12H22O11
There are 12 atoms of Carbon There are 22 atoms of Hydrogen There are 11 atoms of Oxygen
If there is not a subscript listed, it is understood to be 1.
Example: NaCl There is one atom of Sodium There is one atom of Chlorine
You Practice!
NaHCO3
Sodium – 1
Hydrogen – 1Carbon – 1
Oxygen -3
HClHydrogen – 1Chlorine - 1
Coefficient2H2SO4
This means there are 2 compounds of Sulfuric Acid. Think:
H2SO4 H2SO4
Counting the atoms:Hydrogen – 4Sulfur – 2Oxygen - 8
You Practice!!
3H3PO4
Hydrogen – 9Phosphorus – 3Oxygen - 12
2H2O
Hydrogen – 4Oxygen - 2
Chemical Equations
Chemical equations express what is happening in a chemical reaction using symbols.
2K + Cl2 2KCl Reactant Product
yields
Chemical Equations
Because the same atoms are present in a reaction at the beginning (reactants)and at the end (products), the amount of matter in a system does not change.
The Law of Conservation of Matter
Kotz web
Chemical Factory
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The key to chemical reactions!The Law of Conservation of
Mass
In a chemical reaction, no atoms are created or
destroyed. The atoms in the reacting molecules simply re-
arrange to form new molecules.Mass is “conserved.”
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Balancing Equations
The mass of the reactants must equal the mass of the products
Or the number and type of atoms in the reactants is equal to the number and type of atoms in the products
Balancing Equations
Reactants ProductsH 2 2
hydrogen + oxygen water
O2 H2OH2 +
O 2 1
Balancing Equations
H2 + O2 H2O2
Reactants ProductsH 2 2O 2 2
hydrogen + oxygen hydrogen peroxide
XYOU CANNOT CHANGE THE SUBSCRIPTS
Balancing Equations
H2 + O2 H2O
Reactants ProductsH 2 2O 2 1
hydrogen + oxygen water
2
Balancing Equations
H2 + O2 H2O
Reactants ProductsH 2 4O 2 2
hydrogen + oxygen water
2
Balancing Equations
2 H2 + O2 H2O
Reactants ProductsH 4 4O 2 2
hydrogen + oxygen water
2(g) (g) (l)
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
CH4 + 2 O2 CO2 + 2 H2O
Reactants Products 1 C atom 1 C atom 4 H atoms 4 H atoms 4 O atoms 4 O atoms
Cl
Cl
ClH
H
H
ClClCl
Cl HHH
H
H2 + Cl2 HCl H2 + Cl2 2 HCl
reactants products
H
Cl
reactants products
H
Cl
22
2 22 2
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(unbalanced) (balanced)
Unbalanced and Balanced Equations
Practice…___N2 + ___H2 ___NH3 N = N = H = H =
___C2H6 + ___O2 ___CO2 +___H2O
C = C=H = H =O = O =
http://www.physics-chemistry-interactive-flash-animation.com/chemistry_interactive/basic_chemical_reaction_balance_learning.htm
What does H look like?
What does H2 look like?
What does 2H look like?
What does 2H2 look like?
H
H H
H H
H H H H
What does CH3 look like?
What does 3CH look like?
What does 2C + 2H look like?
What does C2 + H2 look like?
What does 2CH3 look like?
C HH
H
H H HC C C
C HH
HC HH
H
C C H H+
H HC C +