Reaksi Kimia.ppt

Chemical Reactions

Reactions and Equations

Classifying Chemical Reactions

Reactions in Aqueous Solutions

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.

Chemical Reactions

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

• Evidence of a chemical reaction

– Change in temperature

– Change in physical properties, odor, gas, or bubbles may form.

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.

• This table summarizes the symbols used in chemical equations.

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.

Representing Chemical Reactions (cont.)

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

Balancing Chemical Equations

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

Balancing Chemical Equations (cont.)

• A 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.

Tulis persamaan kimia untuk reaksi-reaksi berikut .

a . Ketika naftalena padat ( C10H8 ) dibakar di udara , reaksi menghasilkan gas karbon dioksida dan air cair .

b . Meniupkan gas hidrogen sulfida pada mangan ( II ) klorida yang dilarutkan dalam air menghasilkan pembentukan endapan mangan ( II ) sulfida dan asam klorida .

c . Magnesium padat bereaksi dengan gas nitrogen menghasilkan magnesium nitrida padat .

d . Pemanasan gas oksigen difluoride menghasilkan gas oksigen dan gas fluor .

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 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

Types of Chemical Reactions

• 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 (cont.)

• 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.

Decomposition Reactions

• 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.

Replacement Reactions

• 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 (cont.)

• 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.


• 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.


• This table shows the steps to write double replacement reactions.


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

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 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

Aqueous Solutions

• 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 (cont.)

• 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.

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 double replacement reaction.

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

Types of Reactions in Aqueous Solutions (cont.)

• 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)


• 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.


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)

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