Describe how substances react with other substances

Examples:Combustibility – Will a substance burn?Reactivity – Will a substance react with other

substances and how easily?Metals in Groups 1 and 2 are very reactiveSodium (Na) is very reactive, especially with waterDon't try this at home!Hydrogen (H) is also very reactiveThe Hindenburg Disaster - Oh, the humanity!

Stability – Usually do not react with other substancesNoble gases in Group 18Helium (He) is now used in Blimps

Occurs when 2 or more substances are combined and changed into new substances with new properties

Also called chemical reactionsReactants – the substances that change, or reactProducts – the new substances that are producedDuring a chemical reaction, bonds between

atoms are broke and new bonds are formed.Law of Conservation of Matter (Mass) – Matter

cannot be created, nor destroyed. It can only be transformed. So…..

….the starting masses of the reactants is always equal to the final mass of the products

Example:Photosynthesis

6CO2 + 6H2O C6H12O6 + 6O26 molecules of carbon dioxide and 6 molecules of

water are the reactantsSugar and 6 molecules of water are the productsThere are 6 carbon atoms, 12 hydrogen atoms, and

18 oxygen atoms on each side of the equationThis means the equation is balancedA chemical equation must be balanced to satisfy

the Law of Conservation of Matter (Mass)

Temperature changes Instant hand warmers, instant ice packs

Light and sound are producedFireworks

Color changesAutumn leaves, iron rusting, mixing chemicals to

make paintOdor changes

Food spoiling Bubbles or gas form

Alka-seltzerPrecipitate forms

Cave formations made of calcium carbonateExample of a precipitate

Chemical reactions always involve energy changes2 Types of reactions

Exothermic Reactions – Give off energy (heat)Exo = outsideExamples: fireworks exploding, wood burning, iron oxide

(rust) forming, hand warmersEndothermic Reactions – absorb energy (heat)

Endo = insideExamples: instants cold packs, add salt to ice

Activation energy – the smallest amount of energy needed to start a chemical reactionDepends on reactants and other conditions, like

temperature

How fast a reaction occursAffected by 5 main factors

Concentration of reactant particles More particles = faster reaction

Total surface area of the reactantsMore surface area = faster reactionThink alka-seltzer

TemperatureWarmer = faster & colder = slowerOvens & refrigerators

Nature of the reactantsGroups 1 & 2 are very reactive

Adding certain substances to the reaction Inhibitor – slows reactionCatalyst – speeds reaction

Enzymes – catalysts produced by living things – Think salivaElephant Toothpaste – example of a reaction with a

catalyst

Acids – compounds that release hydrogen ions (H+) in waterLemons, oranges, grapefruits – citric acidVinegar – acetic acidSulfuric acid, hydrochloric acid

Have a sour taste - Warning never taste unknown chemicals

Strong acids are corrosive – they eat away or break down materials

Hydrochloric acid in our stomachs helps us digest food

Bases – compounds that release hydroxide ions (OH-) in water – also called alkalineSoapBaking PowderSodium hydroxide

Have a bitter taste – Warning never taste unknown chemicals

Strong bases are corrosive – they eat away or break down materials

Sodium hydroxide is in drain cleaners

Scale used to describe the strengths of acids and bases

Measure of hydrogen ions in the solutionScale ranges from 0-14

7 is neutral (water)0-7 = acid (the lower the number, the stronger the acid)7-14 = base (the higher the number, the stronger the

base)

Substance that changes color in the presence of an acid or base

Litmus paperpH meter