Chapter 1. Chemical Reactions and Equation Part 1
Chemical Reactions and Equation Notes Part 2
Chemical Reactions and Equation InText Question and answer
Chemical Reactions and Equation Chapter end Question and answer
You have already learnt about the physical and chemical reactions. Whenever a chemical change occurs we can say that a chemical reaction has taken place.
Chemical Reaction: Interaction of two or more chemicals that produces one or more new chemical compounds, or alters the properties of the mixed chemicals is known as chemical reactions. The following observations helps us to determine whether a chemical reaction has taken place :
- Change in state
- Change in color
- Evolution of a gas
- Change in temperature
Activity 1.1 :
- Clean a magnesium ribbon about 2cm long by rubbing it with sand paper.
- Hold it with a pair of tongs, burn it with a spirit lamp or burner and collect the ash so formed in a watch glass as shown in figure. Keeping it as far as possible from your eyes
- OBSERVATION: The magnesium ribbon burns with a dazzling white flame and changes into a white powder, this powder is magnesium oxide. It is formed due to the reaction between magnesium and oxygen present in air.
- FORMULA: Mg + O2 → MgO
Activity 1.2 :
- Take lead nitrate solution in a test tube.
- Add potassium iodide solution to this.
- OBSERVATION: A precipitate is formed which is lead iodide and is yellow in colour.
Activity 1.3 :
- Take a few zinc granules in a conical flask or a test tube.
- Add dilute hydrochloric acid to this.
- OBSERVATION: Zinc chloride and hydrogen gas formed.
- Formula : Zn + 2HCl → ZnCl2 + H2
Chemical Equations (Definition): “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.”
Reactants: Reactants are the substances which take part in the Chemical reaction.
Product: Products are the Substances which are formed after the Chemical reaction.
Word Equation: A word equation shows change of reactants to products through an arrow placed between them. The reactants are written on the left hand side (LHS) with a plus sign (+) between them. Similarly products are written on right hand side (RHS) with a plus sign (+) between them. The arrow head points toward the products, and shows the direction of the reaction.
Example: Magnesium + Oxygen → Magnesium Oxide
A chemical equation can be written in shorter way by using the chemical formulas instead of names.
Example: Mg + O2 → MgO
Balanced Chemical Equation (Definition): “A balanced chemical equation occurs when the number of the atoms involved in the reactants side is equal to the number of atoms in the products side”
Steps To Balance Chemical Equation:
- Step 1: To balance a chemical equation, first draw boxes around each formula. Do not change anything inside the boxes while balancing the equation.
Fe + H2O → Fe3O4 + H2
- Step 2: List the number of atoms of different elements present in the unbalanced equation.
- Step 3: To equalize the number of atom, it must be remembered that we cannot alter the formulae of compounds or elements involved in the reaction. For example, to balance oxygen atom we can put coefficient ‘4’ as 4 H2O and not H2O4 or (H2O)4. Now the partly balanced equation becomes:
Fe + 4 H2O → Fe3O4 + H2 (Partially Balanced Equation)
- Step 4: Fe and H atoms are still not balanced. Pick any of these elements to proceed further. Let us balance hydrogen atoms in the partly balanced equation: To equalise the number of H atoms, make the number of molecules of hydrogen as four on the RHS
Fe + 4 H2O → Fe3O4 +4 H2 (Partially Balanced Equation)
- Step 5: Examine the above equation and pick up the third element which is not balanced.
3Fe + 4 H2O → Fe3O4 +4 H2
- Step 6: Finally, to check the correctness of the balanced equation, we count atom of each element on both side of the equation
The numbers of atoms of elements on both side of the equation are equal. This equation is now balanced.
3Fe + 4H2O → Fe3O4 + 4H2
- Step 7: Example 2
CO + 2H2 → CH3OH
Is balanced into
6CO2 + 6H2O → C6H12O6 + 6O2