Physical and Chemical Reactions
physical change
- change of state, solid (s), liquid (l), gas (g), dissolving (aq)
- involves intermolecular bonds rearrangements:
chemical change/ chemical reaction
- a reaction during which substances change into one or more new substances
with different physical and chemical properties
- re-arrangement of intramolecular bonds
reactants --> products
CHEMICAL REACTIONS
Law of Conservation of Matter
- in any chemical reaction, the mass of the products is always equal to the
mass of the reactants, matter can't be created or destroyed
So… making chocolate chip cookies have to have chocolate chips…
recognizing chemical reactions
- generally you will observe one or more of:
- colour change
- formation of a solid (when formed from two aq: precipitate)
- formation of a gas
- heat change
Types of Chemical Reactions
1. Synthesis Reactions
-the combination of two or more simple substances to form a more complex
substance
-also known as combination or addition reaction
A + B --> AB
H2 (l) + O2 (l)--> H2O (g)
balance: 2H2 + O2 --> 2 H2O
--> used to fuel space shuttles: Challenger exploded due to leaky O-ring
special case: Combustion Reaction
-if oxygen rapidly reacts with another element it can form a more complex
compound by burning
C(s) + O2 (g) --> CO2 (g)
S (s) + O2 (g) --> SO2 (g)
2. Decomposition Reactions
-the breakdown of large, more complex molecules or ionic compounds into
smaller and simpler entities
AB--> A + B
2 H2O2 (l) --> O2 (g) + 2 H2O (l)
(hydrogen peroxide)
Coefficient up front tells you that there are two H2O2
special case: thermal decomposition
- decomposition reactions that occur as a result of heating

ex. H2CO3 (aq) (carbonic acid)  CO2 (g) + H2O (l)
So…showing experimental conditions in chemical reactions:
symbol
meaning


C

Fe

uv light

the reactants are heated
reactants are heated to a particular T
reaction is performed in presence of catalyst (helps
rxn go faster)
light energy is necessary for the reaction (in this
case uv light)
Writing Chemical Equations
word equation: identifies reactant and product by name,
ex. sodium + chlorine --> sodium chloride
-not much info, too long
skeleton equation: lists reactants and products with + and --> signs, shows state
ex. Na (s) + Cl2 (g) --> NaCl (s)
-count up the number of atoms: has to be the same on both sides
balanced chemical equation: reflects the law of conservation of mass
ex. 2 Na(s) + Cl2 (g) --> 2 NaCl
Steps in Balancing Chemical Equations
1. is the skeleton equation accurate?
2. balance atoms on both sides, other than H and O
3. polyatomic ions are balanced as a whole IF whole on both sides
4. balance H, O
5. balance lone elements, ex. Cl2
6. check!
ex1. sulfur dioxide gas reacts with oxygen gas to produce gaseous sulfur
trioxide
2 SO2 (g) + O2 (g) --> 2 SO3(g)
ex2. when dissolved in water, copper (II) nitrate reacts with potassium
hydroxide to form a water-soluble potassium nitrate and solid copper (II)
hydroxide precipitate
Cu(NO3)2 (aq) + 2KOH (aq) --> 2KNO3 (aq) + Cu(OH)2 (s)
In Groups Balance
1. KOH + SO2 --> K2SO3 + H2O
2. Al4C3 + H2O --> Al(OH)3 + CH4
3. Na2CO3 + H3PO4 --> Na3PO4 +
H2O + CO2
Worksheets on Balancing:
matter12balancingwsht
matter12balancingwsht2
matter12balancingwsht3
matter12balancingwshtpolyat
4. CaC2 + H2O --> Ca(OH)2 + C2H2
5. Al + NaOH --> Na2AlO3 + H2
6. KNO3 --> KNO2 + O2
UNIT 1 PORTFOLIO
Write a BALANCED chemical equation for each of these
chemical reaction statements.
1) sulphur trioxide gas and water combine to form sulphuric acid
2) when dissolved in water, lead II nitrate and sodium iodide react to make
aqueous lead iodide and sodium nitrate
3) when dissolved beryllium chloride reacts with dissolved silver nitrate in
water, aqueous beryllium nitrate and silver chloride powder are made.
4) solid zinc and aqueous copper II sulphate yield aqueous zinc sulphate and
copper metal
5) aluminum metal reacts violently with chlorine gas to produce a white solid