Chemical Reactions CHAPTER 9. chemical reaction- The process by which one or more substances are...

Chemical ReactionsCHAPTER 9

chemical reaction- The process by which one or more substances are rearranged to form different substances

Evidence that a chemical reaction may have occurred:– Change in temperature

– Change in color

– Odor

– Gas bubbles

– Appearance of a solid

Chemical Reactions

Activity

In your notebook complete the thinking map by

Identifing three examples of chemical reactions you have seen, heard, or smelled in the last 24 hours. Think about activities at home, at school, or outside.

Depict each example

Include any evidence you have that a chemical reaction was occurring.

Representing Chemical Reactions

Chemists use statements called equations to represent chemical reactions.

•Reactants are the starting substances.

•Products are the substances formed in the reaction.

Activity

Label the chemical state each symbol below identifies in a chemical equation.

(s) _________________________________________________________ (g) _________________________________________________________ (aq) _________________________________________________________

(l) __________________________________________________


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)

Both word and skeleton equations lack information about how many atoms are involved in the reaction.

Chemical equation- a statement that uses chemical formulas to show the identities and relative amounts of the substances involved in a chemical reaction.


Activity

In your notebook on the next page Recreate the following table

Organize types of equations that can express a chemical reaction.

In the second column, list the elements (words, coefficients, etc.) that are used to create each equation.

In the third column, rank each equation from 1 to 3, giving a 3 to the equation that provides the most

information, and a 1 to the equation that provides the least information.

Balancing Chemical Equations

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

Coefficient

- 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



The most fundamental law in chemistry is the law of conservation of mass.•Balanced equations show this law.

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.

Classifying Chemical Reactions

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


Chemists classify reactions in order to organize the many types.

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


Types of Chemical Reactions

A + B → AB

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


Types of Chemical Reactions (cont.)

In a combustion reaction, oxygen combines with a substance and releases energy in the form of heat and light.

Heated hydrogen reacts with oxygen to produce heat and water in a combustion reaction. This is also a synthesis reaction.


Types of Chemical Reactions (cont.)

A decomposition reaction 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.


Decomposition Reactions

AB → A + B

A reaction in which the atoms of one element replace the atoms of another element in a compound is called a single replacement reaction.

A + BX → AX + B


Replacement Reactions

A metal will not always replace a metal in a compound dissolved in water because of differing reactivities.

An activity series can be used to predict if reactions will occur.


Replacement Reactions (cont.)

Halogens frequently replace other halogens in replacement reactions.

Halogens also have different reactivities and do not always replace each other.



Double replacement reactions occur when ions exchange between two compounds.



This figure shows a generic double replacement equation.

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

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



ANIMATION

http://connected.mcgraw-hill.com/connected/mediaplayer.do?mediaWidth=320&mediaHeight=240&url=/secure/FFRS98XGP61PDNRXLDR2W@RFT0&contentType=video

This table shows the steps to write double replacement reactions.



This table summarizes different ways to predict the products of a chemical reaction.



LAB

Looking at some examples of chemical reactions

QUIZ TOMORROW

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

A. deconstructive

B. synthesis

C. single replacement

D. double replacement

Section Check

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 Check

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.

Reactions in Aqueous Solutions

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


An aqueous solution contains one or more dissolved substances (called solutes) in water.

The solvent is the most plentiful substance in a solution.


Aqueous Solutions

Water is always the solvent in an aqueous solution.

There are many possible solutes—sugar and alcohol are molecular compounds that exist as molecules in aqueous solutions.

Compounds that produce hydrogen ions in aqueous solutions are acids.


Aqueous Solutions (cont.)

Ionic compounds can also be solutes in aqueous solutions.

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


Aqueous Solutions (cont.)

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

If they react, it is always a double replacement reaction.

Three products can form: precipitates, water, or gases.


Types of Reactions in Aqueous Solutions

Aqueous solutions of sodium hydroxide and copper(II) chloride react to form the precipitate copper(II) hydroxide.

2NaOH(aq) + CuCl2(aq) → 2NaCl(aq) + Cu(OH)2(s)

Ionic equations that show all of the particles in a solution as they actually exist are called complete ionic equations.

2Na+(aq) + 2OH–(aq) + Cu2+ (aq)+ 2Cl–(aq) → 2Na+(aq) + 2Cl–(aq) + Cu(OH)2(s)


Types of Reactions in Aqueous Solutions (cont.)

Ions that do not participate in a reaction are called spectator ions and are not usually written in ionic equations.

Formulas that include only the particles that participate in reactions are called net ionic equations.

2OH–(aq) + Cu2+(aq) → Cu(OH)2(s)



Some reactions produce more water molecules.

No evidence of a chemical reaction is observable.

HBr(aq) + NaOH(aq) → H2O(l) + NaBr(aq)

Without spectator ions H+(aq) + OH–(aq) → H2O(l).



Gases that are commonly produced are carbon dioxide, hydrogen cyanide, and hydrogen sulfide.

2HI(aq) + Li2S(aq) → H2S(g) + 2LiI(aq)



Another example is mixing vinegar and baking soda, which produces carbon dioxide gas.

HCl(aq) + NaHCO3(aq) → H2CO3(aq) + NaCl(aq)

H2CO3(aq) decomposes immediately.

H2CO3(aq) → H2O(l) + CO2(g)



Two reactions can be combined and represented by a single chemical reaction.

SECTION

9.3Reactions in Aqueous

Solutions


Reaction 1

HCl(aq) + NaHCO3(aq) → H2CO3(aq) + NaCl(aq)

Reaction 2

H2CO3(aq) → H2O(l) + CO2(g)

Combined equation

HCl(aq) + NaHCO3(aq) + H2CO3(aq) → H2CO3(aq) + NaCl(aq) + H2O(l) + CO2(g)

Overall equation

HCl(aq) + NaHCO3(aq) → H2O(l) + CO2(g) + NaCl(aq)



What is the solvent in an aqueous solution?

A. hydrogen

B. sodium ions

C. water

D. alcohol

Section Check

An equation that includes only the particles that participate in a reaction is called:

A. net ionic equation

B. spectator ions

C. complete ionic equation

D. reduced ionic equation

Section Check

Key Concepts

Some physical changes are evidence that indicate a chemical reaction has occurred.

Word equations and skeleton equations provide important information about a chemical reaction.

A chemical equation gives the identities and relative amounts of the reactants and products that are involved in a chemical reaction.

Balancing an equation involves adjusting the coefficients until the number of atoms of each element is equal on both sides of the equation.

Study Guide

SECTION

9.1Reactions and

Equations

Classifying chemical reactions makes them easier to understand, remember, and recognize.

Activity series of metals and halogens can be used to predict if single-replacement reactions will occur.

Study Guide

SECTION

9.2Classifying Chemical

Reactions

Key Concepts

In aqueous solutions, the solvent is always water. There are many possible solutes.

Many molecular compounds form ions when they dissolve in water. When some ionic compounds dissolve in water, their ions separate.

When two aqueous solutions that contain ions as solutes are combined, the ions might react with one another. The solvent molecules do not usually react.

Reactions that occur in aqueous solutions are double-replacement reactions.

Study Guide

SECTION

9.3Reactions in Aqueous

Solutions

Key Concepts

The law of conservation of mass requires what in a chemical reaction equation?

A. both sides of the equation to contain the same substances

B. the reactants to have the same amount of molecules as the products

C. both sides to have the same amount of atoms of each element

D. the products to have fewer molecules than the reactants

CHAPTER

9 Chemical ReactionsChapter

Assessment

A reaction that gives off heat is what type of reaction?

A. single replacement reaction

B. double replacement reaction

C. synthesis reaction

D. combustion reaction

CHAPTER


Assessment

Ions that are present in a solution and do not participate in a chemical reaction when another substance is added are called ____.

A. spectator ions

B. reactants

C. products

D. net ions

CHAPTER


Assessment

A double replacement reaction produces all of the following except ____.

A. gases

B. solids

C. light

D. water

CHAPTER


Assessment

What type of reaction is the following?

2H2O(l) + energy → H2(g) + O2(g)

A. synthesis reaction

B. decomposition reaction

C. combustion reaction

D. replacement reaction

CHAPTER


Assessment

What type of reaction is the following?

2H2(g) + O2(g) → 2H2O(l)

A. replacement reaction

B. synthesis

C. decomposition reaction

D. double replacement reaction

CHAPTER

9 Chemical ReactionsStandardized Test Practice

A precipitate forms in a double replacement reaction only if:

A. the reactivities of the compounds differ

B. the new compound is denser than water

C. the new compound is soluble in water

D. the new compound is not soluble in water

CHAPTER


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

A. word equation

B. skeleton equation

C. chemical equation

D. balanced equation

CHAPTER


Predict the type of reaction.

LiBr2 (aq) + 2NaOH (aq) → ____

A. synthesis reaction

B. combustion reaction

C. single replacement reaction

D. double replacement reaction

CHAPTER


Which reactions are essentially the opposite of synthesis reactions?

A. single-replacement

B. decomposition

C. combustion

D. double-replacement

CHAPTER


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