Chemical Reactions and Equations Blog 1

                                                          Chemistry- Chapter 1
                                                Chemical Reactions and Equations

                            "Chemistry is the study of matter and all its aspects"

     

             "Facts are not science- as the dictionary is not literature"- Martin H Fischer

Dear Learners,

Today, we will be discussing about the chapter 1 Chemical Reactions and Equations of our science text book. We will be discussing this chapter sub topic wise for better understanding. 

We appreciate your effort for taking this new step and wish you all to have a great learning ahead.

Learning Outcomes of this chapter: At the end of this chapter, learners will be able to

Content	Learning Outcome	Skill
Occurrence of a Chemical Reactions	-Demonstrate and verify chemical changes -Relate chemical changes to a daily life situations.	Application, Analysis Understanding, Application
Chemical Equation	-Convert chemical change into word equation. - Substitute it by symbols and formula. -Co relate law of conservation to balancing chemical equations -Observe the changes to determine a chemical reaction	Comprehension Comprehension, Application Comprehension, Application, Inter-personal skills Understanding Analysis
Types of Chemical Reactions	-Demonstrate types of chemical reactions -Compare the different types of reactions - Classify the reactions as oxidation or reduction	Application, Analysis and Synthesis Analysis, Critical thinking Comprehension, Analysis
Oxidation in every day life	-Compare the reaction -Apply oxidation in daily life	Analysis and synthesis Critical thinking and environmental awareness

IMPORTANT INSTRUCTIONS:

1. Reading of NCERT Text Book is very important, so refer your book while studying through BLOGS.

2. Complete your Note Books. Write-ups that is in green colour need to be copied in your notebooks rest need to be read carefully for better understanding.

3. You all need to learn the symbols, valency, formulae and polyatomic ions that were discussed in class 9 in chapter 3 Atoms and Molecules.

3. Complete blue box questions and back exercise of your text book in your respective note book.

4. Complete the home assignment given in the last of every blog in your chemistry copy.

So, let us all start!!

Learning Outcomes: At the end of this topic, learner will be able to 

(i) differentiate between physical and chemical changes 

(ii) tabulate the observations taking place during chemical change.

(iii) write chemical equations taking place during chemical change.

(iv) identify various chemical changes happening all around.

(v) identify various characteristic taking place during chemical equation.

(vi) write simple chemical equation.

No matter where you are, or what you are doing, things are changing all around you. Whether it's plants growing or logs burning, or even if you are just eating food, the materials around you are changing in size, shape and structure, releasing or absorbing energy and creating new substances.

But in Chemistry, most changes are divided into two categories: Physical changes and Chemical changes

Physical change: 1. A physical change is something that changes the physical properties of an object or substance like size, shape or form.

Example: Cutting of cloth- Even though the cloth changes shape and size when it is cut, it does not create a new substance. Now, the same cloth is used in making shirt. The shirt is still made of the same substance as the original cloth, just in a new form. It is physical change as no new substance is formed.

Another type of physical change involves changing states of matter and water is a great example of it. Ice melts and become water and water evaporates to become steam but no matter its form, the water is still water.

2. A physical change is the change that can be undone.

Water vapour can condense back into liquid water and liquid water can be frozen back into ice without changing it to a different substance. In fact, many physical changes can be undone.

For example, we know that dissolving sugar into water is a physical change because even though the sugar and the water are mixed together, they do not combine and create a new substance. They are still just sugar and water and they can be separated from each other.

But not all mixtures are as simple to separate as sugar and water. When you mix butter, sugar, flour and eggs, there is not a practical way to separate them but it is still only a physical change.

The chemical change occurs when you put the mixture in the oven and add heat. Baking has many of the indications of a chemical change.

The mixture absorbs heat, it also changes colour and produces an odor and altogether a new substances is formed. Finally, this change cannot be undone as you cannot unbake the cake.

Chemical Change: Chemical changes occurs when the particles of two or more substances are rearranged to form new substance.

For example, when you burn wood, the wood is transformed into a new substance- ash.

Just like in baking, this change cannot be undone. The changing of wood into ash is a chemical change as the wood changes color, releases gases and produces an odor.

Chemical changes are happening all around us. Rusting of metal, fireworks, ripening of fruit and digestion of food is all examples of chemical changes.

So we can say that in a chemical changes always a new substance is formed. They may absorb or release heat. Sometime a chemical change will cause a change in colour, produce an odor and create a sound or produce light.

I am now pretty sure, that you all have clear idea between physical and chemical changes. Now, refer your book, activity 1.1, 1.2, and 1.3 of chapter 1 page 1 and 2.

Lab Activity 1: Burning of Magnesium Ribbon 

https://www.youtube.com/watch?v=epDGHnwaVJY

Lab Activity 2: Reaction between zinc granules and acid

https://www.youtube.com/watch?v=fPMCshL4poQ

Lab Activity 3: Reaction between lead nitrate and potassium iodide solution

https://www.youtube.com/watch?v=6TRuMSjxgYs

So, a chemical reaction can be explained as-

The easily observable features or changes which take place as result of chemical reactions are known as characteristics of chemical reactions.

The important characteristics of chemical reactions are:

              *Evolution of Gas

              *Formation of a precipitate

              *Change in colour

              *Change in temperature

              *Change in state

  

Chemical reactions are the processes in which new substances with new properties are formed. During a chemical reaction, atoms of one elements do not changes into those of another element. Only rearrangement of atoms takes place in a chemical reaction.

The substances which take part in a chemical reaction is called reactants.

The new substances produced as a result of chemical reaction are called products.

The arrow (à) indicates the direction of the reaction in which reactants changes into products.

Now, let write chemical equations happening in the above 3 lab activities.

1. Magnesium burns in air to form magnesium oxide

Mg           +               O₂     à     MgO

(s)                               (g)                (s)

2. Zinc reacts with dil HCl to form zinc chloride and hydrogen gas.  

Zn            +       HCl      à     ZnCl₂   +   H₂

(s)                      (l)                 (l)           (g)

3. Reaction between Lead nitrate and Potassium Iodide.  

            Pb(NO₃)₂      +       KI  à      PbI₂      +      KNO₃

Now, let us all have more examples of some changes.

The chemical reaction is marked by following changes:

1. Change in state: 

(i) Hydrogen and oxygen combines to form water.

2H₂        +  O₂        à      2H₂O

(g)            (g)                   (l)

(ii) Zinc reacts with sulphuric acid to form zinc sulphate and hydrogen gas.

          Zn      +      H₂SO₄           à        ZnSO₄       +     H₂

          (s)                 (l)                               (l)                   (g)

(iii) Methane gas burns in oxygen to give carbon dioxide and water

    CH₄    +     2O₂       à        CO₂       +     2H₂O       +     heat

    (g)              (g)                       (g)                  (g)

(iv) Magnesium burns in air to form magnesium oxide

            Mg           +               O₂     à     MgO

             (s)                          (g)                (s)

The above stated chemical reaction clearly tells us that there can be the change in state during chemical reactions.

To make a chemical equation more informative, the physical states of the reactant and products are mentioned along with their chemical formulae. The gaseous, liquid, aqueous and solid states of reactants and products are represented by the notations (g), (l), (aq), and (s) respectively. The word aqueous is written if the reactant or product is present as a solution in water.

2. Change in Colour:

(i) The chemical reaction between citric acid and purple colored potassium permanganate solution is characterized by a change in colour from purple to colourless.

(ii) The chemical reaction between Sulphur dioxide gas and acidified potassium dichromate (K₂Cr₂O₇/H+) solution is characterized by a change in colour from orange to green.

The above stated chemical reaction clearly tells us that there can be the change in colour during chemical reactions.

3. Evolution of Gas: 

(i) The chemical reaction between zinc and dil sulphuric acid is characterized by the evolution of hydrogen gas.

 Zn    +     dil H₂SO₄   à   ZnSO₄      +     H₂

(ii) Magnesium reacts with dil acid HCl is characterized by the evolution of hydrogen gas.

Mg    +    dil 2HCl        à    MgCl₂      +   H₂

(iii) Sodium carbonate and dil HCl is characterized by the evolution of carbon dioxide gas.

Na₂CO₃     + 2HCl       à    2NaCl       +  CO₂       +   H₂O

The above stated chemical reaction clearly tells us that there can be the evolution of gas during chemical reactions.

NOTE: The Gas evolved should be marked by arrow key facing top side.

4.  Formation of precipitate:

(i) When potassium iodide solution is added to lead nitrate, a yellow ppt of lead iodide is formed.

          KI      +       Pb(NO₃)₂     à   PbI₂      +      2KNO₃

(ii) Sulphuric acid and barium chloride is characterized by the formation of a white ppt of barium sulphate.

        H₂SO₄   + BaCl₂     à  BaSO₄     +  2HCl

(iii) Sodium sulphate reacts with Barium Chloride to form barium sulphate and sodium chloride.

      Na₂SO₄     +    BaCl₂    à  BaSO₄     +    2NaCl

The above stated chemical reaction clearly tells us that there can be the formation of precipitate during chemical reactions.

NOTE: Precipitate should be marked by arrow key facing down side.

5. Change in Temperature:

Exothermic Reactions: When a chemical reaction produces heat energy, then the temperature of reaction increases.

1. The chemical reaction between quick lime (CaO) and water is characterized by rise in temperature.

2. The chemical reaction between zinc granules and sulphuric acid.

Endothermic Reactions: When a chemical reaction absorbs heat energy, then the temperature of reaction decreases. 

1. The chemical reaction between barium hydroxide and ammonium chloride to form barium chloride, ammonia and water result in fall in temperature.

2. Dissolving of ammonium chloride in water.

3. Melting of Ice

NOTE: Sometimes the reaction conditions, such as temperature, pressure, catalyst for the reaction are indication above and/or below the arrow in the equations. For examples

                                           340 atm

CO(g)        +       2H₂(g)        --------->           CH₃OH(l)

                                          

                                       sunlight

6CO2(g)  +   12H₂O(l)  ---------->  C₆H₁₂O₆ (aq)   +  6O₂  (g)  + 6H₂O(g)

                                   Chlorophyll

Links for overview: https://www.youtube.com/watch?v=68a79moN4mY

Home Assignments: Notes and Assignment need to be done in your respective chemistry note book.

1. What is meant by a chemical reaction? Give one example of a chemical reaction.

2. State the characteristics of chemical reactions.

3. Give two characteristics of the chemical reaction which takes place when dilute sulphuric acid is poured over zinc granules.

4.  State two characteristics of the chemical reaction which occurs on adding potassium iodide solution to lead nitrate solution.

5. Why should magnesium ribbon be cleaned before burning in air?

6. State the characteristics of chemical reactions.

7. Give one example of a chemical reaction characterized by the evolution of a gas.

8. Sate one example of a chemical reaction characterized by a change in colour.

9. Write one example of a chemical reaction characterized by the formation of a precipitate.

10. Give one example of a chemical reaction characterized by the change in temperature.

11. State one example of a chemical reaction characterized by a change in state.

12. State one characteristic each of the chemical reactions which take place when:

(i) Dilute hydrochloric acid is added to sodium carbonate.

(ii) Lemon juice is added gradually to potassium permanganate solution.

(iii) Dilute sulphuric acid is added to barium chloride solution.

(iv) Quicklime is treated with water.