Transcript Chemistry: Matter and Change
Section 9.1 Reactions and Equations
• • •
Recognize
evidence of chemical change.
Represent
chemical reactions with equations.
Balance
chemical equations.
chemical change:
a process involving one or more substances changing into a new substance
Chemical reactions are represented by balanced chemical equations.
chemical reaction reactant product chemical equation coefficient 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 Section 9-1
• Chemists use statements called equations to represent chemical reactions.
• •
______________
are the starting substances.
______________
the substances formed in the reaction.
are Section 9-1
Representing Chemical Reactions (cont.)
• In word equations,
aluminum(s) + bromine(l) → aluminum bromide(s)
as “aluminum and bromine react to produce aluminum bromide”.
reads • Skeleton equations use symbols and formulas to represent the reactants and products.
Al(s) + Br(l) → AlBr 3 (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.
Section 9-1
Balancing Chemical Equations
• This figure shows the
balanced
equation for the reaction between aluminum and bromine.
Section 9-1
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.
Section 9-1
Balancing Chemical Equations (cont.)
Section 9-1
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
A 0%
A. A B. B
B 0%
C. C
0%
D. D
C 0% D
Section 9-1
Section 9.1 Assessment What is the coefficient of bromine in the equation 2Al(s) + 3Br 2 (l) → 2AlBr 3 (s)? A.
1
B.
2
C.
3
D.
6
A 0%
A. A B. B
B 0%
C. C
0%
D. D
C 0% D
Section 9-1
Section 9.2 Classifying Chemical Reactions
•
Classify
chemical reactions.
•
Identify
the characteristics of different classes of chemical reactions.
metal:
an element that is a solid at room temperature, a good conductor of heat and electricity, and is generally shiny Section 9-2
Section 9.2 Classifying Chemical Reactions (cont.)
synthesis reaction combustion reaction decomposition reaction single-replacement reaction double-replacement reaction precipitate
There are four types of chemical reactions: synthesis, combustion, decomposition, and replacement reactions.
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
Types of Chemical Reactions
• 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.
• H 2 O → H 2 + O 2 Section 9-2
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.
• CH 4 + O 2 → CO 2 + H 2 O Section 9-2
Types of Chemical Reactions
• 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” Section 9-2
Replacement Reactions (cont.)
•
_______________________
occur when ions exchange between two compounds.
•
“The Perfect Prom”
Section 9-2
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
Section 9.2 Assessment Which of the following is NOT one of the four types of reactions?
A.
deconstructive
B.
synthesis
C.
single replacement
D.
double replacement
A 0%
A. A B. B
B 0%
C. C
0%
D. D
C 0% D
Section 9-2
Section 9.2 Assessment 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
A 0%
A. A B. B
B 0%
C. C
0%
D. D
C 0% D
Section 9-2
Section 9.3 Reactions in Aqueous Solutions
•
Describe
aqueous solutions.
•
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.
solution:
a uniform mixture that might contain solids, liquids, or gases Section 9-3
Section 9.3 Reactions in Aqueous Solutions (cont.)
aqueous solution solute solvent complete ionic equation spectator ion net ionic equation
Double-replacement reactions occur between substances in aqueous solutions and produce precipitates, water, or gases.
Section 9-3
Aqueous Solutions
• An
________________________
contains one or more dissolved substances (called
solutes
) in water.
• The
solvent
a solution. is the most plentiful substance in 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.
Section 9-3