Chemistry_Grade_10-12 (1).pdf

Step 5 check that the atoms are in fact balanced step

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STEP 5: Check that the atoms are in fact balanced. STEP 6 (we will look at this a little later): Add any extra details to the equation e.g. phase. 226
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CHAPTER 12. REPRESENTING CHEMICAL CHANGE - GRADE 10 12.3 Worked Example 49: Balancing chemical equations 1 Question: Balance the following equation: Mg + HCl MgCl 2 + H 2 Answer Step 1 : Because the equation has been written for you, you can move straight on to counting the number of atoms of each element in the reactants and products Reactants: Mg = 1 atom; H = 1 atom and Cl = 1 atom Products: Mg = 1 atom; H = 2 atoms and Cl = 2 atoms Step 2 : Balance the equation The equation is not balanced since there are 2 chlorine atoms in the product and only 1 in the reactants. If we add a coefficient of 2 to the HCl to increase the number of H and Cl atoms in the reactants, the equation will look like this: Mg + 2 HCl MgCl 2 + H 2 Step 3 : Check that the atoms are balanced If we count the atoms on each side of the equation, we find the following: Reactants: Mg = 1; H = 2; Cl = 2 Products: Mg = 1; H = 2; Cl = 2 The equation is balanced. The final equation is: Mg + 2 HCl MgCl 2 + H 2 Worked Example 50: Balancing chemical equations 2 Question: Balance the following equation: CH 4 + O 2 CO 2 + H 2 O Answer Step 1 : Count the number of atoms of each element in the reactants and products Reactants: C = 1; H = 4; O = 2 Products: C = 1; H = 2; O = 3 Step 2 : Balance the equation If we add a coefficient of 2 to H 2 O, then the number of hydrogen atoms in the reactants will be 4, which is the same as for the reactants. The equation will be: CH 4 + O 2 CO 2 + 2 H 2 O Step 3 : Check that the atoms balance Reactants: C = 1; H = 4; O = 2 Products: C = 1; H = 4; O = 4 You will see that, although the number of hydrogen atoms now balances, there are more oxygen atoms in the products. You now need to repeat the previous step. If we put a coefficient of 2 in front of O 2 , then we will increase the number of oxygen atoms in the reactants by 2. The new equation is: CH 4 + 2 O 2 CO 2 + 2 H 2 O When we check the number of atoms again, we find that the number of atoms of each element in the reactants is the same as the number in the products. The equation is now balanced. 227
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12.3 CHAPTER 12. REPRESENTING CHEMICAL CHANGE - GRADE 10 Worked Example 51: Balancing chemical equations 3 Question: Nitrogen gas reacts with hydrogen gas to form ammonia. Write a bal- anced chemical equation for this reaction. Answer Step 1 : Identify the reactants and the products, and write their chemical formulae The reactants are nitrogen (N 2 ) and hydrogen (H 2 ), and the product is ammonia (NH 3 ). Step 2 : Write the equation so that the reactants are on the left and products on the right of the arrow The equation is as follows: N 2 + H 2 NH 3 Step 3 : Count the atoms of each element in the reactants and products Reactants: N = 2; H = 2 Products: N = 1; H = 3 Step 4 : Balance the equation In order to balance the number of nitrogen atoms, we could rewrite the equation as: N 2 + H 2 2 NH 3 Step 5 : Check that the atoms are balanced In the above equation, the nitrogen atoms now balance, but the hydrogen atoms don’t (there are 2 hydrogen atoms in the reactants and 6 in the product). If we put
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