Chemical Reactions and Equations-3 PDF

1.1.1 Writing a Chemical Equation Is there any other shorter way for representing chemical equations? Chemical equations can be made more concise and useful if we use chemical formulae instead of words. A chemical equation represents a chemical reaction. If you recall formulae of magnesium, oxygen a...

1.1.1 Writing a Chemical Equation Is there any other shorter way for representing chemical equations? Chemical equations can be made more concise and useful if we use chemical formulae instead of words. A chemical equation represents a chemical reaction. If you recall formulae of magnesium, oxygen and magnesium oxide, the above word-equation can be written as – Mg + O2 → MgO (1.2) Count and compare the number of atoms of each element on the LHS and RHS of the arrow. Is the number of atoms of each element the same on both the sides? If yes, then the equation is balanced. If not, then the equation is unbalanced because the mass is not the same on both sides of the equation. Such a chemical equation is a skeletal chemical equation for a reaction. Equation (1.2) is a skeletal chemical equation for the burning of magnesium in air. 1.1.2 Balanced Chemical Equations Recall the law of conservation of mass that you studied in Class IX; mass can neither be created nor destroyed in a chemical reaction. That is, the total mass of the elements present in the products of a chemical reaction has to be equal to the total mass of the elements present in the reactants. In other words, the number of atoms of each element remains the same, before and after a chemical reaction. Hence, we need to balance a skeletal chemical equation. Is the chemical Eq. (1.2) balanced? Let us learn about balancing a chemical equation step by step. The word-equation for Activity 1.3 may be represented as – Zinc + Sulphuric acid → Zinc sulphate + Hydrogen The above word-equation may be represented by the following chemical equation – Zn + H2SO4 → ZnSO4 + H2 (1.3) Let us examine the number of atoms of different elements on both sides of the arrow. Element Number of atoms in Number of atoms reactants (LHS) in products (RHS) Zn 1 1 H 2 2 S 1 1 O 4 4 As the number of atoms of each element is the same on both sides of the arrow, Eq. (1.3) is a balanced chemical equation. Let us try to balance the following chemical equation – Fe + H2O → Fe3O4 + H2 (1.4) Chemical Reactions and Equations 3 2024-25