Bell Work

What are the three types of chemical reactions? (refer to your notes)

List one example for each.

Chemical Changes Chemical Changes and Reactionsand Reactions

Properties and Changes of Properties and Changes of MatterMatter

Matter can be described in terms of Matter can be described in terms of two kinds of properties:two kinds of properties:

1.1. Physical propertiesPhysical properties

2.2. Chemical propertiesChemical properties

Physical PropertiesPhysical Properties

A A physical propertyphysical property is a is a characteristic of a substance that can characteristic of a substance that can be observed without changing the be observed without changing the substance into another substance.substance into another substance.

Examples:Examples:– Ice Ice meltingmelting (solid to liquid) (solid to liquid)– Color, hardness, texture, shine, and Color, hardness, texture, shine, and

flexibilityflexibility

Chemical PropertiesChemical Properties

A A chemical property chemical property is a is a characteristic of a substance that characteristic of a substance that describes its ability to change into other describes its ability to change into other substances.substances.

Examples:Examples:– When When magnesiummagnesium burns, it combines with burns, it combines with

oxygen in the air, forming a new substance oxygen in the air, forming a new substance called magnesium oxide.called magnesium oxide.

– Tarnishing and rustingTarnishing and rusting are other are other examples.examples.

Changes of MatterChanges of Matter

A A physical changephysical change is any change is any change that alters the form or appearance that alters the form or appearance of a substance, but does not make of a substance, but does not make the substance into another the substance into another substance. substance.

Other examples include Other examples include bending, bending, crushing, breaking, cuttingcrushing, breaking, cutting, and , and anything else that changes only the anything else that changes only the shape or form of matter.shape or form of matter.

Changes of MatterChanges of Matter

Sometimes when a change occurs in a Sometimes when a change occurs in a substance, the substance itself is substance, the substance itself is changed.changed.

A change in matter that produces one A change in matter that produces one or more new substances is a chemical or more new substances is a chemical change, or change, or chemical reaction.chemical reaction.

Burning gasoline in a car’s engine is an Burning gasoline in a car’s engine is an example. The new substance formed is example. The new substance formed is the car’s exhaust.the car’s exhaust.

Evidence for Chemical Evidence for Chemical ReactionsReactions

Chemical reactions involve two main Chemical reactions involve two main kinds of changes that you can kinds of changes that you can observe:observe:– Formation of new substancesFormation of new substances– Changes in energyChanges in energy

Changes in PropertiesChanges in Properties One way to detect chemical One way to detect chemical

reactions is to observe reactions is to observe changeschanges in in the the propertiesproperties of the materials of the materials involved such as:involved such as:

1.1. ColorColor change change2.2. Formation of a Formation of a precipitateprecipitate (solid (solid

formed from mixing two solutions)formed from mixing two solutions)3.3. Production of Production of gasgas (bubbles) (bubbles)

Not all property changes in matter Not all property changes in matter are chemical, physical changes can are chemical, physical changes can produce similar results as well produce similar results as well (water boiling produces bubbles).(water boiling produces bubbles).

Changes in EnergyChanges in Energy

As matter changes, it can either As matter changes, it can either absorbabsorb or or releaserelease energy. energy.

This change in energy occurs during a This change in energy occurs during a chemical reactionchemical reaction..

Endothermic reactionsEndothermic reactions are reactions are reactions in which energy is in which energy is absorbedabsorbed..

Exothermic reactionsExothermic reactions are reactions are reactions that release energy in the form of that release energy in the form of heatheat..

Rate of ReactionsRate of Reactions

Chemical reactions Chemical reactions don’t don’t all occur at all occur at the same rate. Some occur very the same rate. Some occur very fastfast, , like explosions. Others, like rusting of like explosions. Others, like rusting of metal, occur metal, occur slowly slowly over time.over time.

Chemists can control rate of reactions Chemists can control rate of reactions by changing factors such as by changing factors such as surface surface area, temperature, and area, temperature, and concentration.concentration.

They can also use substances called They can also use substances called catalysts and inhibitors.catalysts and inhibitors.

A A catalyst catalyst is a material that is a material that increases the rate of a reaction by increases the rate of a reaction by lowering the activation energy, or lowering the activation energy, or energy needed to start the reaction.energy needed to start the reaction.– Example: Example: enzymesenzymes in our bodies. in our bodies.

A material used to decrease the rate A material used to decrease the rate of a reaction is an of a reaction is an inhibitorinhibitor. They . They usually work by preventing the usually work by preventing the reactants from combining together.reactants from combining together.– Example: Example: preservatives preservatives added to food added to food

to prevent it from becoming stale or to prevent it from becoming stale or spoiling.spoiling.

Describing Chemical Describing Chemical ReactionsReactions

When you send text messages, you When you send text messages, you often send abbreviated messages…often send abbreviated messages…– ““Sup?” “NM, U?” “OMG!” “CUL8R!”Sup?” “NM, U?” “OMG!” “CUL8R!”

Scientists also use Scientists also use symbolssymbols and and abbreviations abbreviations to describe chemical to describe chemical reactions rather than long sentences.reactions rather than long sentences.

What are Chemical What are Chemical Equations?Equations?

Chemical equations use Chemical equations use formulasformulas and other and other symbolssymbols instead of words instead of words to summarize a reaction.to summarize a reaction.

All chemical equations use formulas All chemical equations use formulas to represent the substances involved to represent the substances involved in a reaction.in a reaction.

A A chemical formulachemical formula is a combination is a combination of symbols that represents the of symbols that represents the elements in a compound.elements in a compound.

Chemical FormulasChemical Formulas

Example:Example:COCO22 is the formula for is the formula for Carbon DioxideCarbon Dioxide..

This formula tells you that this compound This formula tells you that this compound is made up of the elements is made up of the elements carboncarbon and and oxygenoxygen and each molecule has and each molecule has 11 carbon atom and carbon atom and 22 oxygen atoms. oxygen atoms.

Chemical FormulasChemical Formulas

More examples include:More examples include:– WaterWater HH2200

– PropanePropane CC33HH88

– AmmoniaAmmonia NHNH33

– Baking SodaBaking Soda NaHCONaHCO33

Structure of an EquationStructure of an Equation

All chemical equations have a All chemical equations have a common structure.common structure.

A chemical equation tells you the A chemical equation tells you the substances you substances you start withstart with and the and the substances you get substances you get at the endat the end..

The substances at the beginning are The substances at the beginning are called the called the reactants.reactants.

When the reaction is complete, you When the reaction is complete, you have new substances called have new substances called productsproducts..

Structure of an EquationStructure of an Equation

Reactant + Reactant Reactant + Reactant Product + Product + ProductProduct

The number of reactants and products can The number of reactants and products can vary.vary.

Reactant “yields” ProductsReactant “yields” Products

CaCOCaCO33 CaO + CO CaO + CO22

Conservation of MassConservation of Mass

Fe + S Fe + S FeS FeS Iron Sulfur Iron SulfideIron Sulfur Iron Sulfide

If we weighed the iron and sulfur before the If we weighed the iron and sulfur before the reaction takes place, then weigh the product, reaction takes place, then weigh the product, iron sulfide, we would notice… what?iron sulfide, we would notice… what?

14.0 g + 8.0g 14.0 g + 8.0g 22.0 g 22.0 gThe sum is equal to its parts. This is an The sum is equal to its parts. This is an

example of the example of the Conservation of Mass.Conservation of Mass.

Conservation of MassConservation of Mass

This principle, the conservation of This principle, the conservation of mass, states that during a chemical mass, states that during a chemical reaction, matter is reaction, matter is neither created neither created nor destroyednor destroyed..

This means that all the atoms This means that all the atoms present at the start of the reaction present at the start of the reaction are still present at the end.are still present at the end.

Classifying Chemical Classifying Chemical ReactionsReactions

Many chemical reactions can be Many chemical reactions can be classified in one of three categories: classified in one of three categories:

1.1. SynthesisSynthesis

2.2. DecompositionDecomposition

3.3. ReplacementReplacement

SynthesisSynthesis

To To synthesizesynthesize is to put things is to put things together.together.

When two or more elements or When two or more elements or compounds combine to make a more compounds combine to make a more complex substance, the process is complex substance, the process is called called synthesis.synthesis.– Example: Hydrogen and oxygen join Example: Hydrogen and oxygen join

together to form water.together to form water.

DecompositionDecomposition

Decomposition Decomposition breaks down breaks down compounds into simpler products.compounds into simpler products.

2H2H22OO22 2H 2H22O + OO + O22

Hydrogen peroxideHydrogen peroxide eventually eventually decomposes into water and oxygen.decomposes into water and oxygen.

ReplacementReplacement When one element replaces another in a When one element replaces another in a

compound, or when two elements in compound, or when two elements in different compounds trade places, this different compounds trade places, this process is called process is called replacement.replacement.

2Cu2Cu22O + C O + C 4Cu + CO 4Cu + CO22

Copper metal can be obtained by heating Copper metal can be obtained by heating copper oxide with carbon. The carbon copper oxide with carbon. The carbon

replaces the copper.replaces the copper.