Table of contents | |
Chemical Change | |
Chemical Equations | |
Writing a Chemical Equation | |
Skeletal Chemical Equations | |
Balanced Chemical Equations |
A chemical change happens when any two substances interact with each other by gaining, sharing, or donating electrons.
Examples of Chemical Change
Let's do some activities to understand chemical reactions better.
Aim: Perform an activity to show that a chemical reaction has taken place (change in state and change in colour).
Materials Required: Magnesium ribbon, Sandpaper, Tongs, Spirit lamp or burner, Watch-glass, Suitable eyeglasses
Procedure:(i) Clean a magnesium ribbon about 3-4 cm long by rubbing it with sandpaper.
(ii) Hold it with a pair of tongs.
(iii) Burn it using a spirit lamp or burner and collect the ash so formed in a china dish as shown in the Figure above.
(iv) Burn the magnesium ribbon keeping it away as far as possible from your eyes.
Result:
As the magnesium ribbon burns, you will observe a dazzling white flame and the ribbon will change into a white powder, which is the magnesium oxide. This activity shows that a chemical reaction has taken place as there is a change of state of the magnesium ribbon.
Aim: Perform an activity to show that a chemical reaction has taken place (evolution of a gas and change of temperature).
Materials Required: Conical flask (250 mL), cork, glass tube, zinc granules, dilute sulphuric acid.
Procedure:
(i) Set up the apparatus as shown in the above figure.
(ii) Remove the cork and glass tube. Place some dilute sulphuric acid into it.
(iii) Add a few small granules of zinc and immediately close the flask with the cork.
We observe that hydrogen gas is evolved which is indicated by the bubbles.
On touching the flask, we find that it is hotter now than before.
Result:
This activity shows that a chemical reaction has taken place. Before mixing the sulphuric acid and granules of zinc there were no fumes and the flask was at room temperature. But after following all the procedures given, some changes happened and that is the hotter flask than before and bubbles of hydrogen are seen. Thus, there is the evolution of gas and a temperature change.
The description of a chemical reaction in a short form is called a chemical equation. Chemical equations make use of symbols to represent factors such as the direction of the reaction and the physical states of the reacting entities.
For example:
A chemical equation written in the form of symbols and formulae is called a skeletal chemical equation. Such an equation may not be balanced.
Skeletal chemical equationIn the above equations, there are three carbon atoms on the LHS while there is only one carbon atom on RHS hence, this equation is not balanced, now let's see some Balanced chemical equations.
Balanced Chemical Equations
No. of atoms on both sides should be equal
A chemical equation in which the number of atoms of each element on LHS and RHS is equal is called a balanced chemical equation.
Example: Zn + H2SO4 → ZnSO4 + H2
This is a balanced equation because the number of atoms of Zn, H, S, and O is equal on the reactant (LHS) and product (RHS) sides.
Balancing of Chemical Equation
Let us illustrate the balancing of the chemical equations by taking an example:
Example: Fe + H2O → Fe3O4 + H2
The following steps are involved:
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1. What is a chemical change? |
2. What are chemical equations? |
3. How do you write a chemical equation? |
4. What are skeletal chemical equations? |
5. What is a balanced chemical equation? |
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