Foundations of College Chemistry, 14th Ed.
Morris Hein and Susan Arena
Flames and sparks result when aluminum foil is dropped into liquid bromine.
8 Chemical Equations
Reactants: substances consumed during the reaction. Products: substances formed during the reaction.
Atom balance must be maintained in all chemical reactions. All atoms from reactants must appear as part of products.
a A + b B c C + d D
Chemical Equations
• Chemical reactions are processes in which one set
of chemicals are converted to a new set of chemicals
• Chemical reactions are described by chemical
equations.
Evidence for Chemical
Reactions
• A gas is produced.
• A precipitate is formed.
General Structure of Chemical Equations:
1. Reactants and products are separated by an arrow. Reactants are on the left side of the arrow,
products are on the right.
a A + b B c C + d D
Reactants Products
2. Whole number coefficients are placed in front of substances to balance the atoms in the equation. The numbers indicate the units of the substance reacted or formed during the reaction.
The coefficient 1 is not written in a balanced equation.
Chemical Equations
General Structure of Chemical Equations:
3. Information about the reaction (temperature, time) may be placed above or below the reaction arrow.
4. The physical state is written in brackets after the formula of the substance.
a A + b B Δ c C + d D
Δ indicates heat
(g) for gas, (l) for liquid, (s) for solid, (aq) for aqueous
a A (s) + b B (l) c C (g) + d D (s)
Chemical Equations
Symbol Summary
Symbol Significance
Produces (points towards products) (s) Solid (written after substance)
(l) Liquid (written after substance) (g) Gas (written after substance)
(aq) Substance dissolved in an aqueous solution
Heat is added (above or below reaction arrow) Δ
Chemical Equations
In an ordinary chemical reaction, the total mass of
reacting substances is equal to the total mass of
products formed.
In any chemical reaction:
Mass of reactants = Mass of products water hydrogen + oxygen 100.0 g 11.2 g 88.8 g
100.0 g total of products reactants
Law of Conservation of Mass
Chemical Equations
• N
2(g) + 3 H
2(g)
2 NH
3(g)
• must be balanced to satisfy Law of
conservation of mass
• N
2
2
Diatomic Elements
When an equation says “oxygen” or any
•
Copper(II) oxide reacts with ammonia (NH
3)
to yield copper, nitrogen gas, and water.
•
Lead(II) nitrate reacts with potassium
chromate to form lead(II) chromate
(yellow ppt.) and potassium nitrate.
•
Hydrochloric acid reacts with sodium
•
Zinc metal reacts with hydrochloric
acid to produce zinc chloride and
hydrogen gas.
•
Potassium chlorate when heated,
•
Hexane(C
6H
14) burns in oxygen gas to
form carbon dioxide and water.
•
Vinegar(acetic acid) reacts with
baking soda (sodium bicarbonate) to
produce carbon dioxide gas, sodium
acetate, and water.
•
Ammonia reacts with oxygen gas to
•
Iron(III) chloride reacts with ammonium
hydroxide to form iron(III) hydroxide
(brown ppt.) and ammonium chloride.
•
Barium hydroxide and ammonium
Some more examples
•
N
2+ H
2
NH
3•
Be
2C + H
2O
Be(OH)
2+ CH
4•
HCl + CaCO
3
CaCl
2+ H
2O + CO
2Reactions are classified into subtypes to aide in predicting the products of chemical reactions.
Reactions are classified into five major categories:
1. Combination reactions 2. Decomposition reactions
3. Single displacement reactions 4. Double displacement reactions
5. Oxidation-reduction (redox) reactions (Chapter 17)
Types of Chemical Equations
Classifying Reactions by what Atoms
Do
Two reactants combine to give a single product.
where A or B are elements/compounds and AB is a compound.
A + B AB
Representative Examples
metal + nonmetal salt 2 Na (s) + Cl2 (g) 2 NaCl (s)
CaO (s) + H2O (l) Ca(OH)2 (aq)
metal oxide + water metal hydroxide
Violent reaction occurs when Al and Br2 react to form AlBr3.
2 Al (s) + 3 Br2 (l) 2 AlBr3 (s)
Combination Reactions
Classifying Reactions by what Atoms
Do
A single reactant breaks down (decomposes) into two or more products .
AB A + B
Representative Examples
Metal oxides often decompose when heated.
CaCO3 (s) CaO (s) + CO2 (g) Carbonates form CO2 when heated. 2 PbO2 (s) 2 PbO(s) + OΔ 2 (g)
H2O2 decomposes to steam (H2O (g)) and O2. 2 H2O2 (l) 2 H2O (g) + O2 (g)
Decomposition Reactions
Classifying Reactions by what Atoms
Do
• Single Displacement
One element (A) reacts with a compound (BC) to replace one element in the compound, giving a new element (B)
and a different compound (AC). A + BC B + AC
where A and B are metals and A is more reactive. or
A + BC C + AB
where A and C are halogens and A is more reactive.
Zn reacts with HCl, resulting in H2 gas evolution. Example
Zn (s) + 2 HCl (aq) ZnCl2 (aq) + H2 (g)
Single Displacement Reactions
Table listing in order of decreasing reactivity of various elements.
More reactive elements replace less reactive ones. 2 Al (s) + 3 CuCl2 (s) 2 AlCl3 (aq) + 3 Cu (s)
2 Ag (s) + 3 CuSO4 (s) No Reaction
Activity Series
Metal + acid hydrogen + salt
Where A and B are metals and A is more reactive:
2 Al (s) + 3 H2SO4 (aq) Al2(SO4)3 (aq) + 3 H2 (g)
Metal + water hydrogen + metal hydroxide/oxide
2 Na (s) + 2 H2O (l) 2 NaOH (aq) + H2 (g)
Metal (or halogen) + salt metal (or halogen) + salt
Fe (s) + CuSO4 (aq) Cu (s) + FeSO4 (aq)
Cl2 (g) + 2 KI (aq) I2 (s) + 2 KCl (aq)
General Types of Single
Displacement Reactions
Will a reaction occur between Ni and HCl? If so, write the balanced chemical equation.
Based on the reactivity series, Ni is more reactive than hydrogen, so a reaction occurs.
Ni (s) + HCl (aq) H2 (g) + NiCl2 (aq)
Will a reaction occur between Sn and AlCl3? If so, write the balanced chemical equation.
Based on the reactivity series, Sn is less reactive than Al, so no reaction occurs.
Sn (s) + AlCl3 (aq) No Reaction (NR)
Single Displacement Reactions
Cu( ) + AgNO
3( )
Cr ( ) + NiCl
2( )
Fe ( ) + HCl ( )
Cr ( ) + Zn(NO
3)
2( )
Two compounds exchange partners with one another to yield two new compounds.
AB + CD AD + CB
Physical evidence for a double displacement reaction include: heat evolution, formation of a precipitate
or gas production.
PbI2 precipitates from the reaction of Pb(NO3)2 with KI. Pb(NO3)2 (aq) + 2 KI (aq) PbI2 (s) + 2KNO3 (aq)
Double Displacement Reactions
acid + base salt + water + heat Acid/Base Neutralization
HCl (aq) + NaOH (aq) NaCl (aq) + H2O (l) + heat
Metal oxide + acid salt + water + heat
CuO (s) + 2 HNO3 (aq) Cu(NO3)2 (aq) + H2O (l) + heat
Metal Oxide (base) + Acid
General Types of
Double Displacement Reactions
Product solubilities are based on the table in Appendix V Formation of a Precipitate
BaCl2 (aq) + 2 AgNO3 (aq) 2 AgCl (s) + 2 KNO3 (aq)
H2SO4 (l) + NaCl (s) NaHSO4 (aq) + HCl (g) Gas Formation
Insoluble products are indicated by (s)
A gas can also form from a secondary reaction after displacement
2 HCl (aq) + Na2CO3 (aq) 2 NaCl (aq) + H2CO3 (aq) H2CO3 (aq) H2O (l) + CO2 (g)