What we will study:-
- Chemical reactions
- Chemical equations
- Types of chemical reactions.
Why study chemical reactions?
Because it occurs in our day to day life.
For example:- Food left at room temperature during summer starts melting.( Because chemical reaction happen in food )
Medicines taken react in body and we feel better.
Trees derive it's food by photosynthesis that is nothing but chemical reactions.
We respire (food + oxygen--> energy)
Remote cells
Rusting of iron (Fe + O2 ---> rust)
Digestion of food
In vehicle, fuel burns and produces energy and heat.
Observations:- following observations helps us to determine whether a chemical reaction has taken place:-
- Change of state
- Change of colour
- Evolution of a gas
- Change of temperature.
Activity:-
- Clean a magnesium ribbon about 2 cm long by rubbing it with sand paper.
- Hold it with a pair of tong.
- Burn it using a spirit lamp or burner and collect the ash.
Observations:-
- Magnesium ribbon burns with a dazzling white flame and changes into a white powder.
- Magnesium + Oxygen (heat ) -----> Magnesium oxide
- Mg(s) + O2 (g) ∆ ---> MgO (s)
Reactant :- The substances that undergo chemical change in the reaction.
Product :- The new substance, formed during the reaction is the product.
Mg + O2 are reactant and MgO is product.
Writing chemical equation:-
Mg + O2 ∆ --> MgO
CO (g) + 2H2(g) (340 atm) --- > CH3OH (l)
6CO2 (aq) + 6H2O (l) [sunlight and chlorophyll] ----> C6H12O6 (aq) + 6O2(aq)
This is the reaction of photosynthesis.
States of chemicals (Reactants and Products) :-
aq -> aqueous solution (dissolved in water)
l -> liquid
s -> insoluble solid or precipitate
g -> gas
Balanced chemical equation:-
According to law of conservation of mass , mass can neither be created nor be destroyed in a chemical reaction. That means total mass of elements presents in products of a chemical reaction has to be equal to total mass of elements present in reactants.
Number of atoms of each element remains the same before and after a chemical reaction.
Example :-
2Mg + O2 ----> 2MgO
Zn + H2SO4 -----> ZnSO4 + H2
Balanced chemical equation:- Exercise:- Is the equation balanced?
Zn + H2SO4 ----> ZnSO4 + H2
YES
Fe + H2O -----> Fe3O4 + H2
NO
CO (g) + H2 -----> CH3OH
NO
6CO2 + 6H2O (SUNLIGHT + CHLOROPHYLL) --> C6H12O6 + 6O2
YES
Balance a chemical equation:- rule:-
Priority :-
- Balance polyatomic (if exist in both reactants and products)
- Balance metals
- Balance non metals (hydrogen and oxygen at last)
- No fraction should exist in final equation.
- Note:- formula should not be changed.
Exercise :- Balance it
1. N2 + H2 --> NH3
Balanced :- N2 + 3H2 ---> 2NH3
2. CH4 + O2 --> H2O + CO2
Balanced :- CH4 + 2O2 ---> 2H2O + CO2
3. C4H10 + O2 --> CO2 + H2O
Balanced:- 2C4H10 + 13O2 --> 8CO2 + 10H2O
4. AgNO3 + MgCl2 --> AgCl + Mg(NO3)2
Balanced:- 2AgNO3 + MgCl2 ---> 2AgCl + Mg(NO3)2
5. K(ClO3) + KCl ---> KCl + O2
Balanced:- 2K(ClO3) + 2KCl ---> 4KCl + 3O2
6. HNO3 + Ca(OH)2 ---> Ca(NO3)2+ H2O
Balanced:- 2HNO3 + Ca(OH)2 ---> Ca(NO3)2+ 2H2O
7. NaOH + H2SO4 ---> Na2SO4 +H2O
Balanced:- 2NaOH + H2SO4 ---> Na2SO4 + 2H2O
8. NaCl + AgNO3 --> AgCl + NaNO3
Balanced:- NaCl + AgNO3 --> AgCl + NaNO3
9. BaCl2 + H2SO4 ---> BaSO4 +HCl
Balanced:- BaCl2 + H2SO4 ---> BaSO4 +2HCl
10. H2SO4 + KOH ---> K2SO4 + H2O
Balanced:- H2SO4 + 2KOH ---> K2SO4 + 2H2O
11.H3(PO4) + Ca(OH)2 ---> H2O + Ca(PO4)2
Balanced:- 2H3(PO4) + 3Ca(OH)2 ---> 6H2O + Ca(PO4)2
Now write balance chemical equation for:-
1. Hydrogen + Chlorine --> Hydrogen chloride
S.Eq :- H2 + Cl2 --> HCl
B.Ch. Eq:- H2 + Cl2 --> 2HCl
2. Barium chloride + Aluminium sulphate ----> Barium sulphate + Aluminium chloride
S.Eq:- BaCl2 + Al2(SO4)3 ---> BaSO4 + AlCl3
B. Ch. Eq:- 3BaCl2 + Al2(SO4)3 ---> 3BaSO4 + 2AlCl3
3. Barium chloride + potassium sulphate ---> Barium sulphate + potassium chloride
S. Eq:- BaCl2 + K2SO4 ---> BaSO4 + KCl
B. Ch. Eq - BaCl2 + K2SO4 --> BaSO4 + 2KCl
4. Calcium hydroxide + Carbon dioxide --> calcium carbonate + water
S.eq:- Ca(OH)2 + CO2 ---> CaCO3 + H2O
B. Ch. Eq:- Ca(OH)2 + CO2 ---> CaCO3 + H2O
5. Zinc + Silver nitrate ---> Zinc nitrate + Silver
S.eq:- Zn + AgNO3 ---> Zn(NO3)2 + Ag
B. Ch. Eq:- Zn + 2AgNO3 ---> Zn(NO3)2 + 2Ag
6. Aluminium + Copper chloride --> Aluminium chloride + copper
S.eq:- Al + CuCl2 --> AlCl3 + Cu
B.ch. eq.:- 2Al + 3CuCl2 --> 2AlCl3 + 3Cu
Write a balanced chemical equation with state symbols for following reactions:-
1. Sodium hydroxide (in water) reacts with Hydrochloric acid (in water) to produce sodium chloride solution and water.
S.eq:- NaOH (l) + HCl (l) ---> NaCl (aq) + H2O
B.ch. eq:- NaOH (l) + HCl (l) ---> NaCl (aq) + H2O
2. Solutions of Barium Chloride and sodium sulphate in water react to give insoluble barium sulphate and the solution of sodium chloride
S.eq:- BaCl2(aq) + Na2SO4 (aq)---> BaSO4 (s) + NaCl(aq)
B.ch.eq:- BaCl2(aq) + Na2SO4 (aq)---> BaSO4 (s) + 2NaCl(aq)
Type of chemical reaction:-
1. Combination reaction
2. Decomposition reaction
3. Displacement reaction
4. Double displacement reaction
5. Combustion reaction
Other types of chemical reaction:-
1. Redox reaction
2. Acid base reaction (neutralisation reaction)
3. Acid metal reaction
4. Exothermic and endothermic reaction
5. Precipitation reaction
6. Catalysis reaction
7. Biochemical (enzyme) reaction
8. Organic chemistry reactions
9. Photochemical reaction (light)
10. Solid state reactions
11. Corrosion reaction
12. Rancidification reaction.
Note:- other types of reactions are involved in above 5 types.
Combination / synthesis chemical reaction:-
General form :- A + B --> AB
Description:- Two chemical species combine to produce a single compound.
Example:- Quick lime + water --> slaked lime
CaO(s) + H2O(l) --> Ca(OH)2 (aq)
Hydrogen + Oxygen --> Water
2H2(g) + O2(g) --> 2H2O (l)
Sodium + Chlorine --. Sodium chloride
2Na(s) + Cl2(g) --> 2NaCl (s)
Magnesium + Oxygen --> Magnesium oxide
2 Mg (s) + O2(g) --> MgO (s)
Carbon monoxide + Oxygen ---> Carbon dioxide
2CO (g) + O2(g) --> 2CO2
Sulphur dioxide + Oxygen --> Sulphur trioxide
2SO2 (g) + O2(g) ---> 2SO3(g)
Activity:-
Take a small amount of CaO in a Beaker.
Slowly add water to this.
Beaker gets hot.
CaO + H2O --> Ca(OH)2 + heat
Two substances combine to form product.
Decomposition chemical reaction:-
General form:- AB --> A + B
Description :- A single compound decomposes to produce two or more chemical species.
Example:-
1. Water --> Hydrogen + oxygen
2H2O(l) ---> 2H2(g) + O2(g)
2. Hydrogen peroxide ----> water + oxygen
2H2O2 (aq) --> 2H2O(l) + O2(g)
3. Copper carbonate --> copper oxide + Carbon dioxide
CuCO3 (s) --> CuO(s) + CO2(g)
4. Ammonia ---> Nitrogen + Hydrogen
2NH3(g) ---> N2(g) + 3H2(g)
5. Nitrogen triiodide --> Nitrogen + Iodine
2NI3 (s) --> N2(g) + 3I2(s)
Activity:-
Take about 2 gram ferrous sulphate crystals in a dry boiling tube.
Note the colour of the ferrous sulphate crystals.(greenish blue)
Heat the boiling tube over the flame of a burner.
Observe the colour of crystals (red) after heating and pungent smell.
2FeSO4 (s)[ferrous sulphate] ---> Fe2O3(s)[ferric oxide]+ SO2(g) +SO3(g)
Activity 2:-
Take about 2g silver chloride in a dish and note the colour.
Place this dish in sunlight for some time
Observe the colour of silver chloride after some time.
2AgCl (s) [in the presence of sunlight] ---> 2Ag(s) + Cl2
Displacement chemical reaction:-
General form:- AB + C --> CB + A
Description :- An element displaces another element from its compound.
Example:-
1.Hydrochloric acid + Magnesium ---. Magnesium chloride + hydrogen
2HCl + Mg ---> MgCl2 + H2
2. Sulphuric acid + iron ---> Iron sulphate + Hydrogen
H2SO4 (aq) + Fe(s) ---> FeSO4(aq) + H2(g)
3. Nitric acid + Magnesium --> Magnesium nitrate + hydrogen
2HNO3 + Mg --> Mg(NO3)2 + H2
4. Zinc + hydrochloric acid ---> zinc chloride + hydrogen
Zn(s) + 2HCl (aq) --> ZnCl2(aq) + H2(g)
5. Lead + Sulphuric acid --> Lead sulphate + Hydrogen
Pb(s) + H2SO4 (aq) ---> PbSO4 + H2(g)
Activity:-
Take 2 iron nails and two test tubes marked as A and B.
In each test tube , take about 10mL copper sulphate solution.
Immense one nail in copper sulphate solution in test tube B for about 20 minutes.
After 20 mins, take out the iron nails from copper sulphate solution.
Compare the intensity of blue colour of CuSO4 solution in test tubes.
Also , compare the colour of iron nail dipped in copper sulphate solution with one kept aside.
Fe(s) + CuSO4(aq) --> FeSO4 (aq) + Cu(s)
Double displacement chemical reaction:-
General form:- AB + CD ---> AD + CB
Description:- Two different atoms or group of atoms are exchanged in double displacement reaction.
Example :- precipitation and acid base reaction
1. HCl(aq) +NaOH (aq) --> NaCl (aq) + H2O(l)
2. AgNO3 (aq) + NaCl (aq) ---> AgCl + NaNO3(aq)
3. Ba(OH)2 + 2Cu(CNS) ---> Ba(CNS)2 + Cu(OH)2
4. FeS + HCl --> FeCl2 + H2S
Activity:-
Take about 3 mL sodium sulphate solution in a test tube.
In another test tube, take about 3mL of barium Chloride solution.
Mix the two solutions
Observations:- NaCl precipitate out.
Reaction:- Na2SO4 (aq) + BaCl2 (aq) ---> BaSO4 (s) + 2NaCl(aq)
Combustion Chemical reaction:-
C +O2 ---> CO2 + H2
Precipitation chemical reaction:-
General form:-
Solution A + Solution B ---> Insoluble solid C + Solution D
Description:- In a precipitation reaction two solutions are mixed together to produce an insoluble solid which is called the precipitate.
It is a type of double displacement reaction:-
Solubility :- Two solutions can be:-
- Soluble ( Milk + water)
- Moderately Soluble (NaCl + H2O)
- Insoluble [ sand + water]
Solubility is a Physical property of a pure substance . many observations over time have led to some rules about solubility of certain salts.
1. Solubility is dependent on temperature. The solubility of most, but not all salts increases as temperature increases.
Example:- Potassium nitrate has a solubility of 31.2g per 100g of water at 20°C.
A solution that contains the maximum amount of a dissolved solute is said to be saturated.
As it cools , the Solution can no longer hold as much salt so excess amount separates as solid.
If the solution is cooled slowly enough the solid separates as crystals. The process of recrystallization is used to purify substances.
Neutralisation (Acid - Base) chemical reaction :-
General form:- Acid + Base --> salt + water.
Description:- Reactants are a base and an acid and water. The positive charge of the hydrogen ion of acid and negative charge of the hydroxyl group lose their electric charge and become covalent molecules of water.
It is a type of double displacement reaction generally.
Example:- HCl + NaOH --> NaCl + H2O
Exothermic and endothermic chemical reaction:-
Reactions in which heat is given out along with the products are called exothermic reactions.
Reactions in which energy is absorbed are known as endothermic reactions.
Example:- Mg + O2 + heat---> MgO (endothermic reaction)
CaO + CO2 --> CaCO3 + heat (exothermic reaction)
Why is respiration considered as an exothermic reaction? Explain.
Because food we eat combines with oxygen present in atmosphere to produce energy and heat . Since heat is given out . So the reaction is exothermic.
Food + O2 --> energy + heat.
Redox reaction :- Oxidation and Reduction : Reaction that involves gain or loss of oxygen or hydrogen by substances is called redox reaction.
Oxidation is the gain of oxygen or loss of hydrogen.
Reduction is the loss of oxygen or gain of hydrogen.
2Cu + O2 + heat ---> 2CuO
Copper is oxidised
CuO + H2+ heat --> Cu + H2O
Copper is reduced and hydrogen is oxidised.
Corrosion:- redox reaction in daily life.
When a metal is attacked by substances around it such as moisture, acid etc. It is said to corrode and the process is called corrosion.
Example:- black coating on silver
Green coating on copper
Rusting of iron (4Fe + 3O2 --> 2Fe2O3)
Methods to prevent corrosion:-
By applying paints
By oiling
By electroplating
Rancidification:- Redox reaction in daily life :-
When fats and oils are oxidised, they become rancid and their smell and taste change.
Method to prevent rancidification:-
Keeping food in air tight containers help to slow down oxidation.
Chips manufacturers usually flush bags of chips with gas such as nitrogen to prevent the chips from getting oxidised.
By preserve it in fridge.
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