Section 9-1

Section 9-1

Section 9.1 Reactions and Equations

• Recognize evidence of chemical change.

chemical change: a process involving one or more substances changing into a new substance

chemical reaction

reactant

product

chemical equation

coefficient

• Represent chemical reactions with equations.

• Balance chemical equations.

Chemical reactions are represented by balanced chemical equations.

Section 9-1

Chemical Reactions

• The process by which one or more substances are rearranged to form different substances is called a ___________________________

• This involves a chemical change – where you change the identity of the substance.

Section 9-1

Chemical Reactions (cont.)

• Evidence of a chemical reaction

Change in temperature

Exothermic (higher T) vs Endothermic (lower T)

Change in color

Odor, gas, or bubbles may form.

Form a precipitant (????)

Emission of Light

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• Chemists use statements called equations to represent chemical reactions.

• ______________are the starting substances.

• ______________are the substances formed in the reaction.

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Representing Chemical Reactions (cont.)

• In word equations, aluminum(s) + bromine(l) → aluminum bromide(s) reads as “aluminum and bromine react to produce aluminum bromide”.

• Skeleton equations use symbols and formulas to represent the reactants and products.

Al(s) + Br(l) → AlBr3(s)

• Skeleton equations lack information about how many atoms are involved in the reaction.

Section 9-1

Representing Chemical Reactions (cont.)

• A _____________________is a statement that uses chemical formulas to show the identities and relative amounts of the substances involved in a chemical reaction.

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Balancing Chemical Equations

• This figure shows the balanced equation for the reaction between aluminum and bromine.

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Balancing Chemical Equations (cont.)

• A ______________________in a chemical equation is the number written in front of a reactant or product, describing the lowest whole-number ratio of the amounts of all the reactants and products.

• So what are the coefficients on the previous reaction?

• *Table 9.2 in book shows steps for balancing equations

Section 9-1

Why balance equations?

• One of the most fundamental laws in chemistry is the law of conservation of mass.

• Balanced equations show this law.

• A balanced equation is also like a recipe.

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Balancing Chemical Equations (cont.)

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A. A

B. B

C. C

D. D0% 0%0%0%

Section 9.1 Assessment

Which of the following is NOT a chemical reaction?

A. a piece of wood burning

B. a car rusting

C. an ice cube melting into water

D. red litmus paper turning blue

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A. A

B. B

C. C

D. D0% 0%0%0%


What is the coefficient of bromine in the equation 2Al(s) + 3Br2(l) → 2AlBr3(s)?

A. 1

B. 2

C. 3

D. 6

Section 9-2

Section 9.2 Classifying Chemical Reactions

• Classify chemical reactions.

metal: an element that is a solid at room temperature, a good conductor of heat and electricity, and is generally shiny

• Identify the characteristics of different classes of chemical reactions.

Section 9-2

Section 9.2 Classifying Chemical Reactions (cont.)

synthesis reaction

combustion reaction

decomposition reaction

single-replacement reaction

There are four types of chemical reactions: synthesis, combustion, decomposition, and replacement reactions.

double-replacement reaction

precipitate

Section 9-2

Types of Chemical Reactions

• Chemists classify reactions in order to organize the many types.

• Why do this?

• Help predict products before a reaction happens. (Table 9.4 in book)

• A ________________or_________________ is a reaction in which two or more substances react to produce a single product.

Section 9-2

Types of Chemical Reactions (cont.)

• When two elements react, the reaction is always a synthesis reaction.

Section 9-2


• A __________________________is one in which a single compound breaks down into two or more elements or new compounds.

• Decomposition reactions often require an energy source, such as heat, light, or electricity, to occur.

• H2O → H2 + O2

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Types of Chemical Reactions (cont.)

• In a ______________________oxygen combines with a hydrocarbon (made mostly of C and H) and releases carbon dioxide, water, heat, and light.

• CH4 + O2 → CO2 + H2O

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• A reaction in which the atoms of one element replace the atoms of another element in a compound is called a _____________________________

A + BX → AX + B

“The Player at the Prom”

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Replacement Reactions (cont.)

• _______________________occur when ions exchange between two compounds.

•“The Perfect Prom”

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Replacement Reactions (cont.)

• The solid product produced during a chemical reaction in a solution is called a ______________________.

• All double replacement reactions produce either water, a precipitate, or a gas.

Section 9-2

A. A

B. B

C. C

D. D0% 0%0%0%


Which of the following is NOT one of the four types of reactions?

A. deconstructive

B. synthesis

C. single replacement

D. double replacement

Section 9-2

A. A

B. B

C. C

D. D


0% 0%0%0%

The following equation is what type of reaction?

KCN(aq) + HBr(aq) → KBr(aq) + HCN(g)

A. deconstructive

B. synthesis

C. single replacement

D. double replacement

Section 9-3

Section 9.3 Reactions in Aqueous Solutions

• Describe aqueous solutions.

solution: a uniform mixture that might contain solids, liquids, or gases

• Write complete ionic and net ionic equations for chemical reactions in aqueous solutions.

• Predict whether reactions in aqueous solutions will produce a precipitate, water, or a gas.

Section 9-3

Section 9.3 Reactions in Aqueous Solutions (cont.)

aqueous solution

solute

solvent

Double-replacement reactions occur between substances in aqueous solutions and produce precipitates, water, or gases.

complete ionic equation

spectator ion

net ionic equation

Section 9-3

Aqueous Solutions

• An ________________________contains one or more dissolved substances (called solutes) in water.

• The solvent is the most plentiful substance in a solution.

Section 9-3

Aqueous Solutions (cont.)

• Water is always the solvent in aqueous solutions.

• There are many possible solutes:

• ie: sugar, alcohol

• Compounds that produce hydrogen ions in aqueous solutions are acids.

• Ionic compounds can also be solutes in aqueous solutions.

• When ionic compounds dissolve in water, their ions separate in a process called dissociation.

• Gatorade and electrolytes !!!

Section 9-3

Types of Reactions in Aqueous Solutions

• When two solutions that contain ions as solutes are combined, the ions might react.

• If they react, it is always a ____________________________ reaction.

• Three products can form:

• precipitates,

• water, or

• gases.

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Section 9-1