1. Chapter 11 Chemical Reactions

2. Evidence of a Chemical Reaction
Color Change
Energy Change (gets cold or hot)
Exothermic: a reaction or process that releases energy
Endothermic: a reaction or process that requires energy
Odor Change
Precipitate: solid formed from a mixture of solutions
Gas Produced
Irreversible Process
New Properties

3. 2HCl (aq) + Mg (s)  MgCl2 (aq) + H2 (g)
Chemical Equations
Chemical Equation: a representation of a chemical reaction
Formulas of the reactants (on the left) are connected by an arrow with the formulas of the products (on the right)
2HCl (aq) + Mg (s)  MgCl2 (aq) + H2 (g)
Reactants
Products

4. Symbols in chemical equations
aqueous solution (aq):
Substance dissolved in water

5. Catalyst Catalyst: a substance or process that speeds up the reaction
Homogeneous Catalyst:
One in the same physical state as the reactant
2H2O2 (aq) 𝑁𝑎𝐼 𝑎𝑞 2H2O (g) + O2 (g)
Heterogeneous Catalyst:
One in a different physical state
2H2O2 (aq) 𝑀𝑛𝑂2 𝑠 2H2O (g) + O2 (g)
General Examples of Catalysts:
Compounds or elements
Heat 
Light
Aqueous Solutions

6. Steps to balancing chemical equations
Write down your given equation
Write down the number of atom per element that you have on each side of the equation
Use coefficients to balance the elements, one at a time
- Coefficient: Whole number written before the molecule
- Never balance an equation by changing subscripts
Check each atom or polyatomic ion to be sure they are equal
Make sure all coefficients are in the lowest possible ratio

7. Examples
_____ Ca (s) + _____ HCl (aq)  _____ CaCl2 (aq) + _____ H2 (g) _____ Al + _____ H2SO4  _____ Al2(SO4)3 + _____ H2 _____ C7H14 + _____ O2  _____ CO2 + _____ H2O

8. Examples - Answers
Ca (s) + 2 HCl (aq)  CaCl2 (aq) + H2 (g)
2 Al + 3 H2SO4  Al2(SO4)3 + 3 H2
2(C7H O2  7 CO2 + 7 H2O) =
2 C7H O2  14 CO H2O

9. Classifying Chemical Reactions
5 Basic Types of Reactions:
Synthesis (Combination) Reaction:
Two or more substances react to form a single product
A + X  AX
4 Al (s) + 3 O2 (g)  2Al2O3 (s)
Decomposition Reaction:
A single compound broken into two or more products
Most require energy to occur
AX  A + X
2HgO (s)  2 Hg (l) + O2 (g)

10. Classifying Chemical Reactions
Combustion Reaction:
Oxygen reacts with a substance to release energy
Some are also synthesis reactions
C (s) + O2 (g)  CO2 (g)
Most are reactions with hydrocarbons (compounds with carbon and hydrogen)
CH4 (g) + 2 O2 (g)  CO2 (g) + 2 H2O (g)

11. Single Replacement Reaction:
An element replaces on part of a compound
Activity Series: a list of elements in decreasing reactivity
An element will replace anything that is less active
Reactions can be predicted based on the series
A + BX  AX + B or Y + BX  BY + X
Mg (s) + Zn (NO3)2 (aq)  Mg(NO3)2 (aq) + Zn (s)
Double Replacement Reaction:
Exchange of ions between two compounds
May end in a precipitate
AX + BY  AY + BX
Na2S (aq) + Cd(NO3)2 (aq)  CdS (s) + 2 NaNO3 (aq)

12. Reaction Mechanisms 1. Reactions that form water:
Water is produced, chemicals are neutralized
Acid + Base  Salt + Water (Double replacement)
- Acid: begins with a hydrogen atom (H)
- Base: contains hydroxide (OH)
- Salt: ionic compound
Example: 2HI + Cu(OH)2  CuI2 + 2H2O
HCl + NaOH  NaCl + H2O

13. Reaction Mechanisms 2. Reactions that form a metal:
Metal + Salt  Metal + Salt (Single replacement)
Example: 2Fe + 3CuSO4  3Cu + Fe2(SO4)3
Na + AgNO3  Ag + NaNO3

14. Reaction Mechanisms 3. Reactions that form a gas: A. Hydrogen Gas
Metal + Acid  Salt + H2 gas (Single Replacement)
2Na + H2SO4  Na2SO4 + H2
Ca + 2HCl  CaCl2 + H2
B. Hydrogen Sulfide Gas (H2S)
Metal Sulfide + Acid  salt + H2S (Double Replacement)
MgS + 2HCl  MgCl2 + H2S
C. CO2 Gas
(bi) carbonate + acid  salt + water + CO2
HCl + NaHCO3  NaCl + H2O + CO2

15. Reactions in Aqueous Solution
Aqueous Solution: a substance dissolved in water
Solvent: substance doing the dissolving
Water is the universal solvent
Solute: substance being dissolved
Predicting the product state:
Cations and anions will combine and either form a precipitate or no precipitate. When a combination is SOLUBLE it means it was dissolved in water and an aqueous solution formed. INSOLUBLE combinations do not dissolve and instead form a solid precipitate.

16. Representing reactions in aqueous solutions
Molecular equation
Shows formulas of all parts that are mixed
2NaOH(aq) + CuCl2 (aq)  2NaCl (aq) + Cu(OH)2 (s)
Complete ionic
Shows particles as they interact with water
**Only aqueous solutions break into charged particles**
2Na+ + 2OH- + Cu2+ + 2Cl-  2Na+ + 2Cl- + Cu(OH)2(s)
Net ionic
Shows only those particles that are directly involved in the chemical change
Eliminate the ions that remain unchanged – spectator ions
Net ionic: 2OH- + Cu2+  Cu(OH)2(s)

17. No Reactions
Once you complete the Net Ionic Equation, if all the ions “cancel out” there is no reaction.
Occurs when all the reactants and products are aqueous solutions
Example:
NaCl (aq) + KBr (aq)⟶NaBr (aq) +KCl (aq)
Na+ + Cl- + K+ + Br- ⟶ Na+ + Br- + K+ + Cl-