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CHEMICAL REACTIONS AND EQUATIONS - Coggle Diagram
CHEMICAL REACTIONS AND EQUATIONS
Types of reactions
Displacement reaction
reaction in which a more reactive metal displaces a less reactive metal from its compound. AB + C --> AC + B
eg. 1. Fe (s) + CuSO4 (aq) ---> FeSO4 (aq) + Cu (s)
Zn (s) + CuSO4 (aq) --> ZnSO4 (aq) + Cu (s)
Pb (s) + CuCl2 (aq) --> PbCl2 (aq) + Cu (s)
Decompositon reaction
photolytic decomposition
when a decomposition reaction is carried out by sunlight/ light energy
eg.1. 2AgCl (s) (white) + sunlight --> 2Ag (s) (grey) + Cl2 (g)
2AgBr (s) (light yellow) + sunlight --> 2Ag (s) (grey) + Br2 (g). these reactions are used in black and white photography
electrolytic decomposition or electrolysis
when a decomposition reaction is carried out by passing electricity
eg. 2H2O (l) --> 2H2 (g) + O2 (g)
thermal decomposition
when a decomposition reacction is carried out by heating
eg. 1. 2FeSO4 (s) + heat --> Fe2O3 (s) + SO2 (g) + SO3 (G)
CaCO3 (s) + heat --> CaO (s) + CO2 (g). this reaction is used in the manufacture of cement
when a single reactant breaks down to give simple products.
they are mostly endothermic
AB --> A + B
Double Displacement reaction
reactions in which there is an exchange of ions
eg. 1. Na2SO4 (aq) + BaCl2 (aq) --> BaSO4 (ppt) + NaCl (aq)
NaOH + HCl --> NaCl + H2O
Redox reaction
the reaction i which a substance gets reduced and the other gets oxidiesd simultaenously is called oxidation-reduction reaction or redox reaction.
eg. 1. CuO + H2 --> Cu + H2O substance oxidised- H2 substance reduced- CuO oxidising agent- CuO reducing agent- H2
MnO2 + 4HCl --> MnCl2 + H2O + Cl2 substance oxidised- HCl substance reduced- MnO2 oxidising agent- MnO2 reducing agent- HCl
Combination reaction (synthesis reaction)
solution of slaked lime is used for whitewashing walls. calcium carbonate is formed after 2 to 3 days of whitewashing and gives a shiny finish to the walls. Ca(OH)2 (aq) + CO2 (g) --> CaCO3 (s) +H2O (l)
eg. CaO (s) quick lime + H2O (l) --> Ca(OH)2 (aq) (slaked lime) + heat
a reaction in which a single product is formed from 2 or more reactants. A + B --> AB
CHEMICAL REACTION- process by which 1 or more substances react to produce new substances.
OBSERVATIONS THAT HELP TO DETERMINE WHETHER A CHEMICAL REACTION HAS TAKEN PLACE (characteristics of a chemical reaction)
evolution of a gas
Zn + H2SO4 --> ZnSO4 + H2 (g)
change in temp.
CaO (s) + H2O (l) --> Ca(OH)2 + heat
change in colour
CuSO4 (blue) + Fe --> FeSO4 (green) + Cu (brownish)
formation of precipitate
BaCl2 (aq) + Na2SO4 (aq) --> BaSO4 (ppt) + NaCl (aq)
change in state
NH3 (g) + HCl (g) --> NH4Cl (s)
in a chemical reaction the nature and identity of the product is completely changed.
During a chemical reaction- 1. atoms of one element do not change into those of another element. 2. also atoms do not dissapear from the mixture nor do they appear from elsewhere.
Exothermic reactions
reactions in which heat is released along with the formation of products.
eg. 1. CH4 (g) + 2O2 (g) --> CO2 (g) + 2H2O (g)
respiration- C6H12O6 (aq) + 6O2 (aq) --> 6CO2 (aq) + 6H2O + energy
Endothermic reactions
reactions in which energy is absorbed
all decomposition reactions are endothermic bc they need energy in the form of heat, light or electricity for breaking down reactant
Precipitation reaction
any reaction which produces a precipitate. (insoluble substance)
eg. Na2SO4 (aq) + BaCl2 (aq) --> BaSO4 (ppt) + NaCl (aq)
CHEMICAL EQUATIONS- symbolic representation of a chemical equation with the help of symbols and formulae of the substances involved
Types of chemical eq.
Balanced chemical eq.
has equal no. of atoms of diff. elements in the reactants and products eg. 2Mg + O2 --> 2MgO
skeletal chemical eq.
does not has equal no. of atoms in the reactants and products (ie the mass is not the same on both the sides) eg. Mg + O2 --> MgO
Reactants- substances that undergo chemical change Products- the new substances formed
law of conservation of mass- mass can neither be created nor be destroyed in a chemical reaction.
the method of balancing chemical equations is called HIT-AND-TRIAL method as we make trials to balance the equation by using the smallest whole no. coefficient.
HOW TO MAKE A EQ. MORE INFORMATIVE
Writing the PHYSICAL STATES solid- s, liquid- l, gaseous- g,soluble in water- aq,precipitate formed- ppt
reaction CONDITIONS like temp., pressure, catalyst etc, for the reaction are indicated above or below the arrow in the eq.
6CO2 (g) + 12H2O (l) (with sunlight and chlorophyll) --> C6H12O6 + 6O2 (aq) + 6H2O (l)
CATALYST- substances which increase the rate of reactions without actually participating in it
HEAT CHANGES
CORROSION
Rusting
corrosion of iron
4Fe + 3O2 + 3H2O --> 2Fe2O3.H2O (rust) hydrated iron (lll) oxide
causes damage to car bodies, brigdes, iron railings, ships and to all objects made of metals, especially those of iron
Corrosion of Copper
2Cu + H2O + CO2 + O2 --> Cu(OH)2 (green) + CuCO3
when a metal is attacked by substances around it such as moisture, acid etc it is said to corrode
Tarnishing of silver articles
silver reacts with hydrogen sulphide or sulphur present in air and gets ternished
4Ag + 2H2S + O2 --> 2Ag2S (silver sulphide) + H2O
RANCIDITY
when fats and oils are oxidised, they become rancid and their smell and taste change.
Prevention
antioxidants
packaging fat and oil containing foods in nitrogen gas
keeping food in refrigerator
storing food in air tight containers
storing food away from light