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How to determine if a Chemical reaction has taken place?

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How to determine if a Chemical reaction has taken place?

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There are five signs of a chemical change:

1. Color Change.

2. Production of an odor.

3. Change of Temperature.

4. Evolution of a gas (formation of bubbles)

5. Precipitate (formation of a solid)

6. EXAMPLES :-

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Reactive Series And The Easy Way To Learn It

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Reactive Series And The Easy Way To Learn It

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Please - Potassium
Stop - Sodium
Calling - Calcium
Me - Magnesium
A - Aluminium
Cute - Carbon
Zebra - Zinc
I - Iron
Like - Lead
Her - Hydrogen
Calling - Copper
Me - Mercury
Smart - Silver
Perfect - Platinium
Guy - Gold

You Can Learn From This Picture Too. Its Quite Similar To The Written One.

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The term ‘precipitation reaction’ can be defined as “a chemical reaction occurring in an aqueous solution where two ionic bonds combine, resulting in the formation of an insoluble salt”. These insoluble salts formed in precipitation reactions are called precipitates. Precipitation reactions are usually double displacement reactions involving the production of a solid form residue called the precipitate. These reactions also occur when two or more solutions with different salts are combined, resulting in the formation of insoluble salts that precipitate out of the solution.

Example of reactions :
1. AgNO₃(aqueous) + KCl(aqueous) —–AgCl(precipitate) + KNO₃(aqueous)
2. 2KOH(aqueous) + CaCl₂(aqueous)—-Ca(OH)₂(aqueous) + 2KCl(aqueous)
3. AgNO₃(aqueous) + NaCl(aqueous) —- AgCl↓ + NaNO3 (aqueous)

Here a Video to Understand Better ✌️
NAVJEET SINGH XD

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Precipitation reactions | Chemical reactions and stoichiometry | Chemistry | Khan Academy

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What happens to a magnesium ribbon when it burns in air Figure 1.1

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What happens to a magnesium ribbon when it burns in air Figure 1.1

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Observation: When magnesium is placed in a Bunsen burner flame in air it burns with a white flame. The product is a 2Mg+O2=2MgO.
Explanation: At high temperatures the magnesium atoms in the metal combine with the oxygen atoms in the air. A chemical reaction produces magnesium oxide.
Name - Aayush Kashyap IX D
Roll no. - 1

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Roll no. 27
Fig 1.2
This is the figure of formation of hydrogen gas by the action of dilute sulphuric acid on zinc.

Step 1. Take a few zinc granules in a conical flask or a test tube.

Step 2. Add dilute hydrochloric acid or sulphuric acid.

The gas produced in the reaction is hydrogen. Zinc reacts with dilute sulphuric acid to produce hydrogen gas and zinc sulphate.

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Roll no. 27
Fig 1.1
This is the figure of burning of magnesium ribbon in air and collection of magnesium oxide in a watch-glass.

Before performing this activity it is advised to wear eye protection.

Step 1. Clean a magnesium ribbon about 2cm long by rubbing it with sandpaper.

Step 2. Hold it with a pair of tongs. Burn it using a spirit lamp or burner and collect ash so formed in a watch-glass as shown in the figure. Burn the magnesium ribbon keeping it as far as possible from your eyes.

Step 3. When the magnesium metal burns it reacts with oxygen found in the air to form Magnesium Oxide. After it burns, it forms a white powder of the magnesium oxide

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Reactions in which ions are exchanged between the reactants forming a new compounds are called Double Displacement Reactions.
Example :-
Na2SO4 + BaCl2 → BaSO4 + 2NaCl
(sodium sulphate) + (barium chloride) → (barium sulphate) + (sodium chloride)

Precipitation
The reaction in which an insoluble substance (precipitate) is formed by the mixing of two solutions containing salts is called the Precipitation Reaction.
Example :-
Na2SO4 + BaCl2 → BaSO4 + 2NaCl

Name - Sweta Sahni
Roll no. - 24

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RANCIDITY
Definition :- When the substance containing oils and fats are exposed to air they get oxidised and become rancid due to which their smell, taste and colour change. This process is known as rancidity.
Usually substances which prevent oxidation (anti-oxidants) are added to foods contaning fats and oil.

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CORROSION
Definition :- When a metal is attacked by substances around it, such as moisture, acids, etc, it is said to 'corrode'. This process is known as corrosion. For example :- The black coating on silver (Silver Sulphide)
[2Ag+SO₂ → Ag₂S + O₂]
and the green coating on copper (Copper Carbonate)
[ Cu + 2 Co₂ → CuCO₃ + CO]
are examples of corrosion other than the rusting of Iron.
Corrosion causes damage to car bodies, bridges, iron railling, etc..  A HUGE amount of money is sent every year, to replace the rusted iron. Therefore, Corrosion is a serious problem.

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we took a small amount of calcium oxide and added water to it in the beaker.we will observe that the beaker is heated.the temperature is increased. this is because when calcium oxide reacts with water to produce slaked lime(calcium hydroxide) releasing a large amount of heat.this is a combination reaction.

CaO=H2o---->Ca(OH)2+heat

FIG 1.4
we took 2g ferrous sulphate crystals in a dry boiling tube.the color is green.now we heat the boling tube over the flame of a burner or spirit lamp.the color has changed from green.we can also smell the odour of burning sulphur.this reaction is thermal decomposition.

2FeSo4 ----> Fe2o3+So2+So3

sakshi.v
20
10d

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A type of reaction in which reactive elements displaces less reactive element from it's compound or salt  solution is known as Displacement reaction .
A + BC → AC + B

Example =
Na + Al₂Cl2 ------> NaCl + Al

This means Na is more  reactive  then Al .

Roll no - 23

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NAME - KULDIP

The balanced reaction for photosynthesis in word form is

bon dioxide + Water → Glucose  + oxygen.

balanced reaction for photosynthesis in symbol form is

₂ + 6H ₂ O  → C ₆ H ₁₂ O 6 + 6O ₂ + 6H ₂ O

THE SKELETAL
Skeletal chemical equation is a representation of a chemical reaction using chemical formulae of reactants and products. In skeletal chemical equation the mass no of elements in reactant side is not equal to the mass no of elements in product side. Later it has to be balanced by appropriate number of molecules.

For example: Mg + O2 → MgO, it’s a skeleton equation.

Balanced Equation : 2Mg(s) + O2(g) → 2MgO(s).

WORD EQUATION
Word equation means we have to write the chemical reaction in the form of words. Chemical reaction means we have to mention the chemical symbols of the elements to represent the reaction. Nail contains iron in it.
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KULDIP 10 D

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(b)Iron nails and copper sulphate solutions compared before and after the experiment

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(a) Iron nails dipped in copper sulphate solution

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Silver chloride turns grey
In sunlight to form silver
Metal

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A chemical equation  is the symbolic representation of a chemical reaction in the form of symbols and formulae, wherein the reactant entities are given on the left-hand side and the product entities on the right-hand side.
EG OF CHEMICAL EQUATION ->
Zink + sulphuric acid -> zink sulphate + hydrogen
Zn + H₂SO₄ -> ZnSO₄ + H2

BHAVIESH  '6'