1. BALANCING CHEMICAL EQUATIONS

2. USEFUL TERMINOLOGIES Chemical formula: It gives the information about atoms or ions present in the chemical compound. Chemical equation: It is a symbolic representation of reactants (present in left hand side in the chemical reaction) and the products (present in right hand side in the chemical reaction). Reactant ---------  Products Chemical reaction: The process which leads to the transformation of one set of chemical substances to the other set of chemical substances. The Law of Conservation of Mass states that matter cannot be created nor destroyed, only changed. The mass of all of the reactants must equal the mass of all the products. Chemical equations are balanced in order to satisfy the Law of Conservation of Mass

3. LETS BALANCE The equation is said to balanced if it satisfies the following conditions i) The number of atoms should be same on reactant and product side. ii) The coefficients should be an integer. iii) The coefficients should have smallest possible denominator.

4. Some Rules for balancing equations: Use coefficients in front of formulas to balance equations DO NOT change a formula in order to balance an element ( DO NOT change subscripts). DO NOT add terms (atoms or formulas) to the equation Begin balancing with an element that occurs only one time on each side of the arrow. Try to balance the elements one at a time (starting from left to right) If the same polyatomic ion is seen on both sides of the , balance poly atomics (not the elements) Save for last : Elements appearing in more than two formulas Uncombined elements (an element all by itself) DO NOT use a coefficient of “1”; it is implied Check you work. Suggestion: use a tally system below the equation. If the equation is balanced at the start, write the word “balanced” at the end of the equation.

5. LETS TRY AN EXAMPLE Example 1 :_____Na (s) +____Cl 2(g)  _____NaCl (s) The number of Na atoms to the left of the arrow=1 and the number of Na atoms to the right =1 The number of Cl atoms on the left -1 and number to the right of the arrow 2 Without balancing the equation, it looks like an atom of Cl has been destroyed! This is impossible according to the Law of Conservation of Mass. The equation must be balanced so that no atoms/mass is/are lost. If you place a 2 in front of the NaCl, this will give you 2 Na and 2 Cl atoms to the right of the arrow Coefficient applies to all elements in the formula that follows it; coefficient multiplies the subscript 2 NaCl means two units of NaCl Now, place a 2 in front of the Na. Is the equation balanced? Do the number of Na atoms and the number of Cl atoms on the left of the arrow equal the number of Na atoms and Cl atoms to the right of the arrow? Yes, therefore the equation is balanced. Balanced equation:__2__Na (s) +_____Cl 2(g)  ___2__NaCl (s))

6. BALANCING A WORDED EQUATION Step 1: Iron reacts with oxygen to form ferric oxide. Step 2: If we write the chemical equation in words Iron + Oxygen -> Ferric oxide Step 3: Now we balance the chemical equation Fe + O2  Fe2O3 On left hand side 1 atom of Fe and 2 atoms of O and On right hand side 2 atoms of Fe and 3 atoms of O Here the equation is not balanced. To balance the above equation First we balance the oxygen atoms, multiply O2 with 3 in left hand side and multiply Fe2O3 With 2, then Fe + 3 O2  2 Fe2O3 In this equation 6 oxygen atoms are present on both sides. i.e., oxygen atoms are balanced. Now to balance the iron atoms Fe is multiplied with 4 on left hand side, then 4 Fe + 3 O2 ->2 Fe2O3 Its Balanced Equation now.

7. ONE MORE … Step 1: Methane burns with Oxygen to form Carbon dioxide and water molecule Step 2: If we write the chemical equation in words, Methane + Oxygen  Carbon dioxide + water Step 3: Now we balance the chemical equation CH4 + O2 -> CO2 + H2O On left hand side 1 carbon atom, 4 atoms of H,2 atoms of Oxygen and On right hand side we have 1 carbon atom, 3 atoms of oxygen and 2 hydrogen atoms Here the equation is not balanced. But the number of carbon atoms on both sides is same. So now we balance the remaining hydrogen and oxygen atoms in the above equation. First balance the hydrogen atoms, for this purpose multiply H2O with 2, then CH4 + O2 ---> CO2 + 2 H2O Now the number of oxygens are not equal on both sides. So oxygen is multiply with 2 on left hand side, then we get CH4 + 2 O2 ---> CO2 + 2 H2O

8. WRITE THE CHEMICAL EQUATION FOR THE FOLLOWING CHEMICAL REACTION AND THEN BALANCE IT. 1. Liquid water and calcium metal react to produce aqueous calcium hydroxide and hydrogen gas. 2. Solid aluminum oxide decomposes to produce aluminum metal and oxygen gas. 3. Sodium iodide reacts with lead (II) nitrate to produce sodium nitrate and lead (II) iodide. 4. Ethane gas, C 2 H 6, combines chemically with atmospheric oxygen in a combustion reaction to produce carbon dioxide gas and water vapor. 5. The aqueous solutions of lead (II) nitrate and potassium sulfate react to form lead (II) sulfate solid and potassium nitrate.

9. PRACTICE QUESTIONS 1. __NaCl + __BeF 2 --> __NaF + __BeCl 2 2. __FeCl 3 + __Be 3 (PO 4 ) 2 --> __BeCl 2 + __FePO 4 3. __AgNO 3 + __LiOH --> __AgOH + __LiNO 3 4. __CH 4 + __O 2 --> __CO 2 + __H 2 O 5. __Mg + __Mn 2 O 3 --> __MgO + __Mn