Balancing Equations

Conservation of Mass

• Think about the Popcorn Lab, in it we compared mass and volume.

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• Which changed the greatest: Mass or Volume?

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• Can we explain the mass loss versus the volume gain?

Conservation of Mass

• The popcorn lab demonstrates the principle of conservation of mass.

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• The law of the conservation of mass tells us matter can’t be created or destroyed, only transformed. In a reaction the elements change who they pair with, but not their make-up.

Chemical Equations

• Chemical equations are ways for us to model a chemical reaction.

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• Instead of using words we write chemical symbols to show how the reaction progresses.

Chemical Equations

• Each equation is set up the same way.
• Reactants → Products

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• After setting up the equation we need to make sure the elements are the same on both sides of the reaction.

Start with your equation

The first step is starting with your equation:

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NaOH + H₂SO₄ → Na₂SO₄ + H₂O

Identify Amounts

Second step is identify how many elements are present on both sides of the equation.

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NaOH + H₂SO₄ → Na₂SO₄ + H₂O

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Add Coefficients

Each compound starts with the coefficient of 1. Changing these coefficients changes all of the elements in the compound.

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_NaOH + _H₂SO₄ -> _Na₂SO₄ + _H₂O

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Add Coefficients

IMPORTANT!!!!

Note how it is only the number in FRONT of the compound that changes and NOT the chemical formula. Once the chemical formula is known IT DOESN’T CHANGE!

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_NaOH + _H₂SO₄ -> _Na₂SO₄ + _H₂O

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Practice 2

__KCl + __CaF₂ --> __KF + __CaCl₂

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1. __NaCl + __BeF₂ --> __NaF + __BeCl₂

2. __FeCl₃ + __Be₃(PO₄)₂ --> __BeCl₂ + __FePO₄

3. __AgNO₃ + __LiOH --> __AgOH + __LiNO₃

4. __CH₄ + __O₂ --> __CO₂ + __H₂O

5. __Mg + __Mn₂O₃ --> __MgO + __Mn

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1. 2 NaCl + 1 BeF₂ --> 2 NaF + 1 BeCl₂

2. 2 FeCl₃ + 1 Be₃(PO₄)₂ --> 3 BeCl₂ + 2 FePO₄

3. 1 AgNO₃ + 1 LiOH --> 1 AgOH + 1 LiNO₃

4. 1 CH₄+ 2 O₂ --> 1 CO₂ + 2 H₂O

5. 3 Mg + 1 Mn₂O₃ --> 3 MgO + 2 Mn

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Word Equations

Steps to Balancing Word Equations

1. Write a word equation to identify the reactants and products.
2. Translate names of compounds into their formula.
1. Follow the steps for formula writing and don’t count the number of elements yet!
3. Balance the equation using the prior process.

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Word Equations

• Word Equations are chemical equations with words replacing the element symbols

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• It is necessary to practice writing word equations because they are the first step in translating to a balanced equation

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Word Equations

• Word Equations come from story problems about reactions.
• Example: hydrogen chloride and zinc metal reacted to form zinc chloride and hydrogen gas.
• We start by separating the chemicals into reactants and products.

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Word Equations

• Example: hydrogen chloride and zinc metal reacted to form zinc chloride and hydrogen gas.

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hydrogen chloride + zinc → zinc chloride + hydrogen

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Word Equations to Balanced Equation

Next is the translation from words to chemical formulas. Remember how to recognize ionic and covalent compounds. *And don’t forget BrINClHOF!

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hydrogen chloride + zinc → zinc chloride + hydrogen

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HCl + Zn → ZnCl₂ + H₂

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Word Equations to Balanced Equation

Finally, balance the formula equation to get the number of elements the same on each side.

hydrogen chloride + zinc → zinc chloride + hydrogen

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HCl + Zn → ZnCl₂ + H₂

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2 HCl + Zn → ZnCl₂ + H₂

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Steps to Balancing Word Equations

• Write a word equation to identify the reactants and products.
• Translate names of compounds into their formula.
• Follow the steps for formula writing and don’t count the number of elements yet!
• Balance the equation using the prior process.

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Steps to Balancing Word Equations

Practice 1: A reaction occurs when nitrogen trihydride gas is added to water resulting in ammonium hydroxide.

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Steps to Balancing Word Equations

Practice 2: A precipitate of silver chloride is formed along with sodium nitrate when sodium chloride is added to a silver nitrate solution.

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