Unit 6 Chemical reactions: Lesson 2 types of chemical reactions

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CHEMICAL CHANGE – THINGS YOU REMEMBER…

SIGNS:
●BUBBLES OF GAS APPEAR
●A PRECIPITATE FORMS

• (SOLID APPEARS)

●RELEASE OF ENERGY

• (THE TEMPERATURE CHANGES)

●A COLOR CHANGE
●BURNING SOMETHING
●THERE IS A DIFFERENT SMELL

EXAMPLES:
•GASOLINE IS IGNITED
•CAR RUSTING
•MILK GOES SOUR
•BREAD BECOMES TOAST
•A TREE BURNING
•HYDROGEN PEROXIDE BUBBLES
IN A CUT
•PHOTOSYNTHESIS

TYPES OF CHEMICAL REACTIONS

• ENDOTHERMIC- ABSORBS HEAT
• EXOTHERMIC RELEASES HEAT

ALL CHEMICAL REACTIONS CAN BE DESCRIBED IN TERMS OF
SOMETHING MOVING. THE 6 TYPES OF REACTIONS ARE
CLASSIFIED AS FOLLOWS:
•MOVEMENT OF ELECTRONS:

1.

ADDITION (SYNTHESIS)

2.

DECOMPOSITION

3.

SINGLE REPLACEMENT

4.

COMBUSTION

•MOVEMENT OF IONS:

5.

DOUBLE REPLACEMENT

•MOVEMENT OF PROTONS:

6. ACID-BASE

SYNTHESIS (DIRECT COMBINATION)

A+B🡪 AB

• 2 OR MORE SUBSTANCES COMBINE TO FORM A SINGLE MORE

COMPLEX SUBSTANCE

• EXAMPLES:

• 2H2 + 2O2🡪 2H2O

• C + O2🡪 CO2
• CAO + H2O 🡪 CA(OH)2

• S8 + 12O2🡪 8 SO3

• ONLY ONE PRODUCT

DECOMPOSITION (AB🡪 A+B)

• A SINGLE SUBSTANCE IS BROKEN DOWN INTO TWO OR

MORE SIMPLER SUBSTANCES

• MOST REQUIRE THE ADDITION OF HEAT

• EXAMPLES:

• 2H20🡪 2H2 + O2
• 2HGO🡪 2HG + O2
• 2NACL🡪 2NA + CL2

• ONLY ONE REACTANT

COMBUSTION

• A COMPOUND IS BURNED IN THE PRESENCE OF

OXYGEN

• PRODUCTS ARE ALWAYS CO2 + H2O+HEAT

• EXAMPLES:

• CH4 (G) + 2O2 (G) 🡪 CO2 (G) + 2H2O (G)

• 2C8H18 (L) + 25O2🡪 16CO2 (G) + 18 H2O (G)

SINGLE REPLACEMENT (A+BC🡪 B+AC)

​OCCUR WHEN A FREE ELEMENT BECOMES AN ION AND AN ION

IN SOLUTION BECOMES A NEUTRAL ATOM

• MORE ACTIVE ELEMENT REPLACES A

• LESS ACTIVE ELEMENT  (TABLE J)

• EXAMPLES:

  • Zn (s) + H2SO4 (Aq) 🡪 ZnSO4 (Aq) + H2 (g)

​

• Cl2 (g) + 2NaBr (Aq) 🡪 Br2 (l) + 2NaCl (aq)

​

• Cu (s) + 2AgNO3 (Aq) 🡪 2Ag (S) + Cu(NO3)2 (Aq) 

​

• Ag(s) + 2Cu(NO3)2 (Aq) 🡪 2Cu (S) + 2Ag(NO3) (Aq)

ACTIVITY SERIES AND REPLACEMENT REACTIONS

•HAVE TO THINK ABOUT WHICH ELEMENT
IS MORE REACTIVE TO MAKE SURE A
REACTION WILL OCCUR

•ZN + PBNO3→ ZNNO3 + PB
•FE + ZNSO4→ NO REACTION

DOUBLE REPLACEMENT (AB+CD🡪 AC+BD)

⚫ TAKES PLACE BETWEEN TWO IONIC COMPOUNDS THAT ARE

DISSOLVED IN WATER

⚫ CATION OF ONE COMPOUND REPLACES THE CATION OF THE

OTHER COMPOUND

⚫ 2 COMPOUNDS ON BOTH SIDES

⚫ WILL ONLY OCCUR IF ONE OF THREE THINGS HAPPENS:

◦ AN INSOLUBLE COMPOUND FORMS AND IS REMOVED AS A

PRECIPITATE

◦ A H+ ION UNITES WITH AN OH- ION AND FORMS WATER

◦ A GAS FORMS AND ESCAPES THE REACTION VESSEL

DOUBLE REPLACEMENT (OR DISPLACEMENT)

• EXAMPLES:

• AgNO3 (aq) + NaCl (aq)🡪 AgCl (s) + NaNO3 (aq)

• NaOH (aq) + HCl (aq) 🡪 NaCl (aq) + H2O (L)

• NH4Cl (aq) + NaOH (aq)🡪 NH4OH (aq) + NaCl (aq)🡪

• NH4Cl (aq) + NaOH (aq)🡪 NH3(g) +H2O(L) + NaCl (aq)

ACID-BASE REACTION

•THIS IS A SUB-CLASS OF A DOUBLE REPLACEMENT
REACTION
•HAPPENS BECAUSE OF A MOVEMENT OF PROTONS (H+)
•THE PRODUCTS ARE ALWAYS H2O AND A SALT

•AB + CD → SALT + H2O

EXAMPLE: HCl + NaOH → NaCl + H2O

SALT WATER

*THIS IS FOR AN ACID AND A BASE THAT ARE EQUAL
STRENGTH ONLY.

REACTION RECAP

•SYNTHESIS (COMBINATION)

•END WITH ONLY 1
COMPOUND

•DECOMPOSITION

•START WITH ONLY 1
COMPOUND

•SINGLE REPLACEMENT

•EACH SIDE HAS A
SINGLE ELEMENT AND A
COMPOUND

•COMBUSTION

•PRODUCTS WILL
ALWAYS BE CO2 + H2O
AND ENERGY

•DOUBLE REPLACEMENT

•EACH SIDE HAS 2
COMPOUNDS

•ACID-BASE REACTION

•PRODUCTS WILL
ALWAYS BE H2O AND A
SALT (IONIC
COMPOUND) OF SOME
FORM

WHAT IS A CHEMICAL PROCESS?

•MOST CHEMICAL REACTIONS OCCUR WHEN SUBSTANCES ARE IN WATER

THERE ARE 4 PROCESSES THAT CAN OCCUR WHEN A SUBSTANCE MAKES CONTACT WITH WATER:

1. DISSOLVE (DISPERSION)

   • When the forces that hold molecules together (intermolecular forces or ionic bonds) are broken. 

2. DISSOCIATION 

   • SEPARATION OF IONS OF AN IONIC COMPOUND

     • EXAMPLE: SALT DISSOLVING IN WATER

3. IONIZATION

   • FORMATION OF IONS IN SOLUTION FROM A COVALENT/MOLECULAR SOLUTE

     • EXAMPLE: HCl DISSOLVING IN WATER

4. PRECIPITATATION

   • When two insoluble ions form a solid ( a precipitate, see solubility chart)

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