chemical reactions five types of chemical reactions: 1. combustion 3. decomposition 4. single...
TRANSCRIPT
Chemical ReactionsChemical Reactions
Five Types of Chemical Reactions:
1. Combustion
3. Decomposition
4. Single Displacement
5. Double Displacement
2. Synthesis
Evidence that a chemical reaction Evidence that a chemical reaction has taken place?has taken place?
Colour / Odour Change
Formation of a gas or solid
Difficult to reverse
Release/Absorption of Energy (heat)
More commonly known as burning
1. Combustion Reactions1. Combustion Reactions
Easily identified (release of heat)
HeatFuel
For combustion 3 things need to be present:
Oxygen
1. Combustion Reactions1. Combustion Reactions
Sulphur (in gasoline):
S(s) + O2(g) SO2(g) + Heat
2 H2(l) + O2(l) 2 H2O(g) + Heat
Rocket Fuel:
Common OxidesCommon OxidesResulting from Combustion ReactionsResulting from Combustion Reactions
Combustion SituationElement in
Reactant
Common
Oxide
Coal in a coal-fired electricity generator carbon CO2 (g)
Burning of rocket fuel Hydrogen H2O (g)
Commercial production of sulphuric acid Sulphur SO2 (g)
Lightning strikes and volcanoes Nitrogren NO2 (g)
2. Synthesis Reactions2. Synthesis Reactions
combination of two or more simple substances combining to form a more complex substance.
A + B AB
+
MgMg(s)(s) + O + O2(g)2(g) MgO MgO22
Synthesis of Magnesium Oxide
Other ExamplesOther Examples
C(s) + O2(g) CO2(g)
S(s) + O2(g) SO2(g)
Synthesis Reactions:
3. Decomposition Reactions3. Decomposition Reactions
Breaking down large, complex molecules or ionic compounds into smaller, simpler entities.
AB A + B
+
HH22OO2(l)2(l) O O2(g)2(g) + H + H22OO(l)(l)
Decomposition of Hydrogen PeroxideDecomposition of Hydrogen Peroxide
2 2
4. Single Displacement4. Single Displacement
reaction of an element with a compound that produces a new element and new compound.
A + BC AC + B
Single Displacement of Zinc and ChlorineSingle Displacement of Zinc and Chlorine
HClHCl(aq)(aq) + Zn + Zn(s) (s) H H2(g)2(g) + ZnCl + ZnCl2(aq)2(aq)2
Chemical Reactions in SolutionChemical Reactions in Solution
SOLUTE – is a pure substance (usually lesser in quantity) that is dissolved in another pure substance called the “SOLVENT”
AQUEOUS SOLUTION – a solution in which water is the solvent (aqua – meaning water).
SolubilitySolubilitySolutions are homogenous mixtures of solutes and
solvents.
Solubility is the measure of how much of the solute can possibly dissolve in a known amount of solvent. If a substance has high solubility in water, it has a subscript of (aq). However, if it isn’t very soluble it will start to precipitate out and will have a (s) subscript for solid.
Use a Solubility TableUse a Solubility Table
Is calcium hydroxide soluble? Is sodium flouride soluble?What about lead (II) Iodide?
5. Double Displacement5. Double Displacement
reaction of two compounds, where the positive and negative ions in their respective compounds switch places to form two new compounds. This can only happen with ionic compounds
AB + CD AD + CB
Double DisplacementDouble Displacement
A double displacement reaction only occurs if one of the following three results are seen:
a precipitate is formed a gas is produced a change of pH occurs (a neutralization reaction)
** If the products are both soluble then the reaction is NR (no reaction)
Double Displacement of Lead and PotassiumDouble Displacement of Lead and Potassium
Pb(NOPb(NO33))2(aq)2(aq) + KI + KI(aq) (aq) PbI PbI2(s)2(s) + KNO + KNO3(aq)3(aq)22
Precipitate: A solid that is formed as a result of the chemical reaction of two aqueous solutions.
More ExamplesMore Examples
FeCl3(aq) + Na2(SO4)2(aq) → ?
NR – both are soluble
HCl(aq) + LiOH(aq) → ?
pH change – neutralization reaction, products are LiCl & H2O
2HNO3(aq)+ K2CO3(aq)→ CO2(g)+H2O(l) + 2 KNO3(aq)
gas produced – therefore double displacement
Percentage CompositionPercentage Composition
Composition of Common
Alloys
Alloy % Composition Property
Brass Cu (70%)
Zn (30%)
Harder and more resistant to corrosion than copper
Stainless Steel
Fe (80%)
Cr (18%)
Ni (1%)
Si (1%)
More resistant to corrosion then iron
18K gold Au (75%)
Ag (13%)
Cu (12%)
Harder and less malleable than 24K gold
Percent CompositionPercent Composition Percentages are calculated by weight
How much gold (in grams) is there in 10g sample of 18K yellow gold where the % composition is 75% Au?
Answer: mass of Au = (75% / 100) x 10g
= 7.5 g
Therefore there is 7.5 g of pure gold in a 10g sample of 18K yellow gold.