A chemical equation is a shorthand way of describing a chemical reaction. It uses symbols of elements and formulas of compounds in place of words to describe a chemical change or reaction. 1. The formulas and symbols of reactants are written on the left side of the equation. 2. The formulas and symbols of products are written on the right side of the equation. 3. A plus sign (+) is placed between different reactants and different products. 4. The reactants are separated from the products by an arrow (→) pointing in the direction of the reaction. For a reversible reaction, double arrow (⇄) is used. 5. The physical states of substances may be indicated by the symbols (s) for solid, (l) for liquid, (aq) for aqueous solution, and (g) for gases. 6. The equation is then balanced by inserting appropriate coefficients for the products and reactants. For the word equation Sulfur trioxide+Water → Sulfuric acid we can substitute the formulas for reactants and products, following the above rules, and obtain a chemical equation for the reaction as: SO3(g)+H2O(l) −→ H2SO4(aq) A chemical equation is balanced when it has the same number of atoms of each element on either side of the equation. Thus, a balanced equation obeys the law of conservation of mass. That is, atoms are not ‘created’ or ‘destroyed’ in writing a chemical equation. 1. Formulate and write a word equation if necessary from experiment or problem. 2. Write the unbalanced equation using the rules for writing chemical formulas. 3. Balance the equation to make sure the law of conservation of mass is observed. (a) Inspect both sides of the equation to identify atoms that need to be balanced. (b) Balance one element at a time by placing a suitable coefficient to the left of the formula containing the element. Note that a coefficient placed in front of the formula affects all the atoms in the formula. For example, 2 H2O implies 2 molecules of water containing 4 atoms of hydrogen and 2 atoms of oxygen. (c) Never attempt to balance an equation by changing subscripts because this will change the formulas of the compounds.
Keywords: balancing chemical equations, combination reaction, decomposition reaction, displacement reaction, double decomposition reaction, metathesis reaction, neutralization reaction, synthesis reaction
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