Chemical Reactions

Chemical Reactions are all around us

Describing Chemical Reactions

• chemical change - rearrangement of atoms to form a new substance

Has new chemical and

physical properties

Evidences of a Chemical Reaction

• Produce a gas• Produce a solid

(precipitate)

• Color change

• Odor change

• Temperature change–Exothermic–Endothermic

• Give off heat/light

• Produce sound

Chemical Reaction vs. Physical Change

• To prove a chemical change took place, you have to do a chemical analysis• Properties of a new substance must

differ from the original substance

Analogy!

• Physical change is like printing a word in a different font, it’s the same word just looks different!

stampedes stampedes

• Chemical change is like scrambling letters to form new words

made + steps stampedes

Remember…

• All changes of state: Solid Liquid Gas– Evaporation– Condensation – Melting– Freezing

Are Physical Changes!

Physical or Chemical Change?

Physical or Chemical Change?

Physical or Chemical Change?

Physical or Chemical Change?

Physical or Chemical Change?

Physical or Chemical Change?

Physical or Chemical Change?

Physical or Chemical Change?

Rotten Egg

Physical or Chemical Change?

Physical or Chemical Change?

Physical or Chemical Change?

Physical or Chemical Change?

Physical or Chemical Change?

What causes Chemical Reactions?

Reaction and Energy Changes

• Chemical Reactions either RELEASE or ABSORB energy.

Release Energy Example:

• Natural Gas– Methane + Oxygen Carbon Dioxide + Water +

ENERGY

Absorb Energy Example:

• Photosynthesis– Carbon Dioxide + Water + ENERGY Oxygen +

Glucose

Chemical Equations

• Equations are used to represent chemical reactions–Reactants – starting substances–Products – new substances

Reactants Product

Chemical Equations

• Arrow always points to the product

Hydrogen + Oxygen Water

Mercury Oxide Liquid Mercury + Oxygen

Sodium Chloride Sodium + Chlorine

Word Equations – uses names

• Names of the reactants separated by a +• Arrow separates reactants from products• Names of products separated by a +

Hydrogen + Oxygen Water

Example:

Formula Equations – uses symbols

• Symbol of the reactants separated by a +• Arrow separates reactants from products• Symbol of the products separated by a +

H₂ + O₂ H₂O

Example:

Writing word and formula equations:

• Mercury oxide is heated to form liquid mercury and oxygen

• Word =

• Formula =

Common symbols in equations

• → : produces or forms• + : plus• (s) : solid• (l) : liquid• (g) : gas• (aq) : aqueous - dissolved in water

Add the symbols

Hydrogen + Oxygen Water

Mercury Oxide Mercury + Oxygen

Sodium Chloride Sodium + Chlorine

Common symbols in equations

• Reversible

• 1803 a scientist observed the formation of sodium carbonate crystals at the edge of a salt lake 2NaCl + CaCO3 → Na2CO3 + CaCl2. He recognized this as the reverse of the familiar reaction Na2CO3 + CaCl2→ 2NaCl + CaCO3. He reasoned that the excess of salt in the lake helped push the "reverse" reaction towards the formation of sodium carbonate

Common symbols in equations

• ______ The element symbol above the arrow indicates a catalyst. –A catalyst is something that speeds up

the reaction but is not changed during the reaction, so it goes above the arrow.

KI

Review writing ionic compounds

1.Magnesium Nitride

2.Iron (III) Oxide

3.Sodium Sulfide

4.Copper (II) Chloride

Seven diatomic elements:• Hydrogen (H2)• Nitrogen (N2)• Oxygen (O2)• Fluorine (F2)• Chlorine (Cl2)• Iodine (I2)• Bromine (Br2)

Write these on back of

periodic table!

Common Polyatomic Ions

• Write these down on the backs of your periodic tables

Writing polyatomic compounds

• Aluminum Hydroxide• Mercury (II) Phosphate• Aluminum Sulfate• Copper (II) Bromide• Lead (II) Chlorite• Silver Cyanide• Ammonium Oxide