# If we put a coefficient of 3 in front of the hydrogen

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don’t (there are 2 hydrogen atoms in the reactants and 6 in the product). If we put a coefficient of 3 in front of the hydrogen (H 2 ), then the hydrogen atoms and the nitrogen atoms balance. The final equation is: N 2 + 3 H 2 2 NH 3 Worked Example 52: Balancing chemical equations 4 Question: In our bodies, sugar (C 6 H 12 O 6 ) reacts with the oxygen we breathe in to produce carbon dioxide, water and energy. Write the balanced equation for this reaction. Answer Step 1 : Identify the reactants and products in the reaction, and write their chemical formulae. Reactants: sugar (C 6 H 12 O 6 ) and oxygen (O 2 ) Products: carbon dioxide (CO 2 ) and water (H 2 O ) Step 2 : Write the equation by putting the reactants on the left of the arrow, and the products on the right C 6 H 12 O 6 + O 2 CO 2 + H 2 O Step 3 : Count the number of atoms of each element in the reactants and the number of atoms of each element in the products 228

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CHAPTER 12. REPRESENTING CHEMICAL CHANGE - GRADE 10 12.3 Reactants: C=6; H=12; O=8; Products: C=1; H=2; O=3; Step 4 : Change the coefficents of the molecules until the number of atoms of each element on either side of the equation balance. It is easier to start with carbon as it only appears once on each side. If we add a 6 in front of CO 2 , the equation looks like this: C 6 H 12 O 6 + O 2 6 CO 2 + H 2 O Reactants: C=6; H=12; O=8; Products: C=6; H=2; O=13; Step 5 : Change the coefficients again to try to balance the equation. Let’s try to get the number of hydrogens the same this time. C 6 H 12 O 6 + O 2 6 CO 2 + 6 H 2 O Reactants: C=6; H=12; O=8; Products: C=6; H=12; O=18; Step 6 : Now we just need to balance the oxygen atoms. C 6 H 12 O 6 + 6 O 2 6 CO 2 + 6 H 2 O Reactants: C=6; H=12; O=18; Products: C=6; H=12; O=18; Exercise: Balancing simple chemical equations Balance the following equations: 1. Hydrogen fuel cells are extremely important in the development of alternative energy sources. Many of these cells work by reacting hydrogen and oxygen gases together to form water, a reaction which also produces electricity. Balance the following equation: H 2 ( g ) + O 2 ( g ) H 2 O ( l ) 2. The synthesis of ammonia (NH 3 ), made famous by the German chemist Fritz Haber in the early 20th century, is one of the most important reactions in the chemical industry. Balance the following equation used to produce ammonia: N 2 ( g ) + H 2 ( g ) NH 3 ( g ) 3. Mg + P 4 Mg 3 P 2 4. Ca + H 2 O Ca ( OH ) 2 + H 2 5. CuCO 3 + H 2 SO 4 CuSO 4 + H 2 O + CO 2 6. CaCl 2 + Na 2 CO 3 CaCO 3 + NaCl 7. C 12 H 22 O 11 + O 2 CO 2 + H 2 O 8. Barium chloride reacts with sulphuric acid to produce barium sulphate and hydrochloric acid. 9. Ethane (C 2 H 6 ) reacts with oxygen to form carbon dioxide and steam. 10. Ammonium carbonate is often used as a smelling salt. Balance the following reaction for the decomposition of ammonium carbonate: ( NH 4 ) 2 CO 3 ( s ) NH 3 ( aq ) + CO 2 ( g ) + H 2 O ( l ) 229
12.4 CHAPTER 12. REPRESENTING CHEMICAL CHANGE - GRADE 10 12.4 State symbols and other information The state (phase) of the compounds can be expressed in the chemical equation. This is done by placing the correct label on the right hand side of the formula. There are only four labels that can be used: 1. (g) for gaseous compounds 2. (l) for liquids

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