Chemistry 11 – Notes on Chemical Reactions 2 Balancing Chemical Equations: • A chemical equation is balanced if there is the same number of each type of atom on each side of the equation. Example: (NH 4 ) 2 S + Pb(NO 3 ) 2 ! NH 4 NO 3 + PbS Guideline to balancing equations: 1. Put coefficient to balance (big numbers in front of each chemical) 2. Balance entire groups (eg. polyatomic ions: NO 3 - , NH 4 + ) first if they are found on both sides. 3. Balance metal atoms next . 4. Try to avoid balancing H , and O ’s until the end if possible. These atoms are often found several times throughout an equation. 5. If there are fractions in the equation (eg. ½ O 2 ), multiply the equation by the whole number (eg. 2) to eliminate the fraction. 6. Always double check your equation after balancing. Answer: (NH 4 ) 2 S + Pb(NO 3 ) 2 ! 2 NH 4 NO 3 + PbS Example #2: N 2 + H 2 ! NH 3 Answer: Balance N first N 2 + H 2 ! 2NH 3 Hydrogens in NH 3 now have a coefficient in front of it, check on the other side of the equation for H’s and balance them too! N 2 + 3H 2 ! 2NH 3 Subscripts: • A chemical equation can also show the states in which the reactants and products exist. The states of chemicals are shown by including the following symbols in brackets immediately after the chemical formula. (s) = solid, (l) = liquid, (g) = gas, (aq) = aqueous [“dissolved in water”] Solid liquid gas aqueous I I dissolved in H2O 11 PPT " " powder " " dissolved " " crystal " Solution "
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Balancing Chemical Equations€¦ · Balancing Chemical Equations: • A chemical equation is balanced if there is the same number of each type of atom on each side of the equation.
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Chemistry 11 – Notes on Chemical Reactions
2
Balancing Chemical Equations:
• A chemical equation is balanced if there is the same number of each type of atom on each side of the equation.
1. Put coefficient to balance (big numbers in front of each chemical)
2. Balance entire groups (eg. polyatomic ions: NO3-, NH4
+) first if they are
found on both sides.
3. Balance metal atoms next .
4. Try to avoid balancing H , and O ’s until the end if possible. These atoms
are often found several times throughout an equation.
5. If there are fractions in the equation (eg. ½ O2), multiply the equation by the
whole number (eg. 2) to eliminate the fraction.
6. Always double check your equation after balancing.
Answer: (NH4)2S + Pb(NO3)2 ! 2 NH4NO3 + PbS
Example #2: N2 + H2 ! NH3 Answer: Balance N first N2 + H2 ! 2NH3
Hydrogens in NH3 now have a coefficient in front of it, check on the other side of the equation for H’s and balance them too! N2 + 3H2 ! 2NH3 Subscripts:
• A chemical equation can also show the states in which the reactants and products
exist. The states of chemicals are shown by including the following
symbols in brackets immediately after the chemical formula.
(s) = solid, (l) = liquid, (g) = gas, (aq) = aqueous [“dissolved in water”]
Solid liquid gas aqueous
I I dissolved in H2O
11 PPT" "
powder"
"dissolved "
"
crystal "Solution
"
Chemistry 11 – Notes on Chemical Reactions
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Example: Solid zinc reacts with a hydrochloric acid solution to form hydrogen gas and dissolved zinc chloride. Zn (s) + 2HCl (aq) ! H2 (g) + ZnCl2 (aq)
• Note: “crystals”, “powder”, and “precipitate” all mean the phase is a solid ! Defn:
• Precipitate: a solid formed when two liquid or aqueous solutions react. Predicting Products
• The key to predicting products is to be able to identify the type of reaction that the reactants will undergo
Example:
1. NO2 ! ?
• There is only one compound on the reactant side. This is a decompose
tion reaction!
• The compound will break down into its individual elements.
Therefore: 2NO2 ! N2 + 2O2
2. Mg + ZnSO4 ! ?
• There is one element and one compound on the reactant side. This is a
single replacement reaction!
• The metals (or non-metals) will switch places. Therefore: Mg + ZnSO4 ! Zn + MgSO4
3. Al + O2 ! ?
• There are two elements by themselves on the reactant side. This is a
synthesis reaction!
• The elements combine to form one compound.
Therefore: 4Al + 3O2 ! 2Al2O3
¢Always Cag )
↳ Translate E include States
Enes ,t 2 HCl cap
→ Hug , t In Clzcaq,
solid substance that forms by mixing multiple
Solms .
identify chemical rxn
Dbreak Into smaller pieces .
2 NO 2 it Nz +202
SR
→Mg t ZnS04 En + Mgs Ot
S
one compound
4 At +302 → 2 At 203
Chemistry 11 – Notes on Chemical Reactions
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4. HCl + KOH ! ?
• There is an acid and a base on the reactant side. This is a neutralization
reaction (a special case of double displacement reaction)!
• Water is one product, and the other ions combine to form a salt.
Therefore: HCl + KOH ! KCl + H2O
5. C2H2 + O2 ! ?
• There is a hydrocarbon compound and oxygen on the reactant side. This
is a combustion reaction!
• The products will be CO2 and H2O
Therefore: 2C2H2 + 5O2 ! 4CO2 + 2H2O
ACID BASE
N
DR
salt
HCl t KOH → H2O t Kel
c
CO2 t H2O
" CHO"
2 even 4 2
XC2H2 t 502 → * CO2 t XHZO✓ Odd
4 t I = 5
evene) XZ
8 t 2 = 10
Home Fun
④ ass : Finish marking HI # 8
marking } QUE next
Finish HI # 9 class !
@ Home Finish pre lab 5C
Chemistry 11 – Notes on Chemical Reactions
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Type of Reaction Definition General Formula Examples What to look for!
Synthesis (S) Combination of two or more
substances to form a compound
A + B ! AB
C + O2 ! CO2
H2 + Cl2 ! 2HCl
Two elements as reactants.
Decomposition (D) Breaking down a molecule into simpler substances AB ! A + B
2KClO3 ! 2KCl + 3O2
2Ag2O ! 4Ag + O2
One compound as a reactant.
Single Replacement (SR)
Replacing one atom in a compound by another atom AX + B ! BX + A
Cu + 2AgNO3 ! Cu(NO3) 2 + 2Ag
Cl2 + 2KI ! I2 + 2KCl
Element and a compound react.
Double Replacement (DR)
Exchange of atoms or groups between two different
compounds AX + BY ! AY + BX Pb(NO3) 2 + 2KI ! PbI2 + 2KNO3