12.1

How do chemist use balanced chemical equations?

• Chemist use balanced chemical equations as a basis to calculate how much molecules are needed or how much product will be formed in a reaction.

• Chemist use balanced chemical equations as a basis to calculate how much reactant is needed or how much product will be formed in a reaction.

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In Terms of what quantities can you interpret a balanced chemical equation?

• A balanced chemical equation can be interpreted in terms of different quantities, including numbers of atoms, molecules, or moles;mass;and volume.

• A balanced chemical equation can be interpreted in terms of different quantities, including numbers of reactants and properties

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NGSS.HS-PS1-7

Define Stoichiometry

• The portion of chemistry that deals with numerical relationships in chemical reactions; calculations of quantities of substances involved in chemical equations

• The portion of chemistry that deals with product relationships in chemical reactions; calculations of quantities of substances involved in chemical equations

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4 ways to interpret a balanced chemical equation

• atoms, moles, molecules, mass

• stoichiometry, volume, mass, STP

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How is a balanced equation similar to a recipe?

• A balanced chemical equation provides the same kind of quantitative properties that a recipe does.

• A balanced chemical equation provides the same kind of quantitative information that a recipe does.

What quantities are always conserved in chemical reactions?

• mass and volume are conserved in every chemical reaction

• molecules and volumes are conserved in chemical reaction

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NGSS.HS-PS1-7

Interpret the given equation in terms of relative numbers of representative particles, numbers of molecules, and masses of reactants and products

2K(s) + 2H₂O(l) -> 2KOH(aq) + H₂(g)

• Representative particles: 2 atoms K + 2 molecules H20 → 2 formula units KOH + 1 molecule H2

  Moles: 3 mol K + 2 mol H2O → 2 mol KOH + 1 mol H2

  Mass: 88.2 g K + 36.0 g H2O → 112.2 g KOH + 2.0 g H2

• Representative particles: 2 atoms K + 2 molecules H20 → 2 formula units KOH + 1 molecule H2

  Moles: 2 mol K + 2 mol H2O → 2 mol KOH + 1 mol H2

  Mass: 78.2 g K + 36.0 g H2O → 112.2 g KOH + 2.0 g H2

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NGSS.HS-PS1-7

Balance the equation: C₂H₅OH(l) + O₂(g) -> CO2₂(g) + H₂O (g)

Show that the balanced equation obeys the law of conservation of mass.

• C2H5OH + 3O2 = 2CO2 + 3H2O.

  The law of conservation of mass states that mass cannot be created nor destroyed. The balanced equation obeys the law of conservation of mass because on both the reactants and the product side the number of molecules are the same. Because both the reactants and product are even, mass is not being created nor destroyed.

• C3H6OH + 5O3 = 5CO2 + 6H3O.

  The law of conservation of mass states that mass can be created and destroyed. The balanced equation obeys the law of conservation of mass because on both the reactants and the product side the number of molecules are the same. Because both the reactants and product are even, mass is not being created nor destroyed.

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NGSS.HS-PS1-7