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 +