Chapter 8 Lecture

Basic ChemistryFourth Edition

Chapter 8 Chemical Reactions8.1 Equations for Chemical Reactions

Learning Goal Identify a balanced chemical equation and determine the number of atoms in the reactants and products.

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Key Math Skills• Solving Equations (1.4D)Core Chemistry Skills• Writing Ionic Formulas (6.2, 6.4) • Naming Ionic Compounds (6.3, 6.4)• Writing the Names and Formulas for

Molecular Compounds (6.5)

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Chapter 8 Readiness

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Chemical Change

A chemical change occurs when a substance is converted into one or more new substances.

When silver tarnishes, silver metal (Ag) reacts with sulfur (S) to form a black substance we call tarnish (Ag2S).

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Chemical Reaction

A chemical reaction• involves chemical change• represents the formation of a new substance

with new propertiesDropping an antacid

tablet in water produces CO2 gas when NaHCO3 reacts with citric acid (C6H8O7).

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Visual Evidence of a Chemical Reaction

The following evidence is an indication that a chemical reaction may have occurred.

A chemical equation tells us the materials needed and the products formed in a chemical reaction.

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Writing a Chemical Reaction

When charcoal is burned in a grill, the carbon in charcoal combines with oxygen from the air to form water and carbon dioxide gas.

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Chemical Equations

In chemical equations

• reactants are written on the left, products on the right

• two or more formulas on one side are separated by a (+) sign

• the delta sign, (Δ), indicates heat is used to start the reaction

• physical states are abbreviated, including solid (s), liquid (l), gas (g), and aqueous (aq)

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Chemical Equations

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Learning Check

Identify the visible evidence of a chemical reaction in each of the following:

A. Methane gas in an outdoor heater burns with a blue flame.

B. Bleach removes stains from a shirt.

C. Bubbles of CO2 are released when baking soda is mixed with vinegar.

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Solution

Identify the visible evidence of a chemical reaction in each of the following:

A. Methane gas in an outdoor heater burns with a blue flame.

heat and a flame

B. Bleach removes stains from a shirt.color change (color removed)

C. Bubbles of CO2 are released when baking soda is mixed with vinegar.formation of a gas (bubbles)

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Identifying a Balanced Equation

Every chemical reaction is written as a balanced equation, such that atoms of each element are the same in the reactants and products.

To balance a reaction, coefficients are written in front of chemical formulas.

2H2(g) + O2(g) 2H2O(g)

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Balanced Chemical Equations

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Learning Check

State the number of atoms of each element on thereactant and the product sides of the equations.

A. P4(s) + 6Br2(l) → 4PBr3(g)

B. 2Al(s) + Fe2O3(s) → 2Fe(s) + Al2O3(s)

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Solution

State the number of atoms of each element on the reactant and the product sides of the equations.

A. P4(s) + 6Br2(l) → 4PBr3(g)

4 P 4 P

12 Br 12 Br

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Solution

State the number of atoms of each element on the reactant and the product sides of the equations.

B. 2Al(s) + Fe2O3(s) → 2Fe(s) + Al2O3(s)

2 Al 2 Al

2 Fe 2 Fe

3 O 3 O

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Learning Check

Determine if each equation is balanced or not.

A. Na(s) + N2(g) → NaN3(s)

B. C2H4(g) + H2O(l) → C2H5OH(l)

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Solution

Determine if each equation is balanced or not.

A. Na(s) + N2(g) → NaN3(s)

1 Na 1 Na

2 N 3 N Equation is not balanced.

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Solution

Determine if each equation is balanced or not.

B. C2H4(g) + H2O(l) → C2H5OH(l)

2 C 2 C

6 H 6 H

1 O 1 O Equation is balanced.