Chemical Reactions and Equations Blog 3

Dear Learners,

I hope you all have started following the instruction given in previous two blogs. I also presume that you all have practiced the method of writing chemical formulae.

I feel you all have not only taken the notes but also completed the home assignment in your respective chemistry note book.

In the previous blog, we have discussed about the simple technique for writing chemical formulae. Let me help you all, to recall-

While writing the chemical formulae for compounds, we write the constituent elements and their valencies. Then we must crossover the valencies of the combining atoms to get the correct formula of a compound.

Now let us discuss the ways to write and balance a chemical equation.

Happy Learning!

At the end of this topic, learners will be able to 

 (i) write the chemical equations

(ii) balance the chemical equations.

Key Instructions:

Green lines are meant to be written in note book.

Red lines are meant to be read carefully for understanding the concept.

Home Assignment need to be done in note book.

Let us all begin!!!!

                                        CHEMICAL EQUATIONS

In blog 1, we have discussed that magnesium ribbon is burnt in oxygen it gets converted to magnesium oxide. It can be written in a shorter form. The word equation for the above reaction would be-

Magnesium   +    Oxygen     à      Magnesium oxide

Learners, we need to know that the substances that undergo chemical change in the above reactions are magnesium and oxygen. These are called as REACTANTS.

Whereas, the new substance magnesium oxide formed in the reaction is called as PRODUCT.

Here all learners, we need to understand, a word equation shows a change of reactants to products through an arrow placed between them. The reactant are written on the left-hand side or LHS with a plus sign (+) between them.

Like way, products are written on the right-hand side or RHS. Here also, plus sign (+) is written between two or more reactants, if formed.

Further, you should also know that the arrowhead points towards the products and shows the direction of reaction.

https://www.youtube.com/watch?v=ApJvQQLL2iY

How to write a Chemical Equations?

Chemical equations can be made more concise and useful if we use chemical formulae instead of words. A chemical equations represents a chemical reaction.

So, let us write the above word equation again and then replacing it by chemical symbols

         Magnesium     +      oxygen         à     magnesium oxide

    

                   Mg             +       O2             à         MgO          ------(Eq1)

Let us take few more examples

2.    Zinc            +    Sulphuric acid       à     zinc sulphate     +   hydrogen

        Zn             +     H₂SO₄                à      ZnSO₄              +     H_{2       -----(Eq 2)}

3.  Magnesium  +  Hydrochloric acid    à   Magnesium chloride  +   hydrogen

 Mg              +    HCl                   à     MgCl₂           +     H₂

https://www.youtube.com/watch?v=NRCn8z8gb1w

I hope now you getting more clear idea about writing chemical equations now let us discuss the techniques of balancing chemical equations.

Balancing of Chemical Equations

Learner, you all must be feeling what the importance of balancing chemical equations is. Well your doubt is absolutely correct.

But, recall the law of conservation of mass that you all have studied in class IX. According to this law, mass can neither be created nor destroyed in a chemical reaction. That means, the total mass of reactant is equal to the total mass of product.

So, in order to obey this law of conservation of mass, balancing of chemical equation tends to become very important.

So let us start.

Let us compare the two equations and then examine the number of atoms of different element on both sides of the arrow.

                Mg             +       O2             à         MgO      …………eq 1

    

                Zn              +    H2SO4         à         ZnSO4   + H2      …….eq2

Equation 1				Equation2
Elements	Number of atoms in reactant (LHS)	Number of atoms in products (RHS)		Elements	Number of atoms in reactant (LHS)	Number of atoms in products (RHS)
Mg	1	1		Zn	1	1
O	2	1		H	2	2
				S	1	1
				O	4	4

Now compare the two equation. You can easily see here, in equation (i) the number of atoms in reactant is not equal to the number of atoms in product whereas in equation 2 the number of atoms in reactant is equal to number of atoms of product.

https://www.youtube.com/watch?v=RPYYmmwH9dc

Read page no 3 and 4 of your text book for better understanding.

https://www.youtube.com/watch?v=8lZIwGFd4U0

Learner, we will meet you tomorrow positively.

Home Assignments

1. Blue box questions on page 6

2. Do Q no 3,4,5,6,7,9 given on page 15

3. Complete your notebook.