balancing equations notes website 2018.notebook November 12, 2018

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2 Particle model and Balancing Equations Used to show chemical reactions have occured. Matter is made up of atoms and molecules and is subject to change. Counting atoms in a molecule NaCl 3 NaCl Na 2 SO 4 2 Na 2 SO 4 3 CuSO 4 C 5 H 11 OH 3 C 5 H 11 OH Ca 3 (PO 4 ) 2 3 Ca 3 (PO 4 ) 2 Cu(NO 3 ) 2 2 Cu(NO 3 ) 2 3 NH 4 Cl 2

3 Various symbols can be used to represent the molecules. Na 2 Na 2 H 2 H 2 SO 4 Cu(NO 3 ) 2 2 Cu(NO 3 ) 2 Ca 3 (PO 4 ) 2 3 Ca 3 (PO 4 ) 2 3

4 Chemical reactions can be represented by a balanced chemical equation: HCl + NaOH > NaCl + H 2 O 4 Al + 3 O 2 2 Al 2 O 3 Fe 2 O CO 2 Fe + 3 CO 2 HNO H 2 NH H 2 O 4

5 Conservation of Matter (Mass) Matter is never created or destroyed, it is just changed. Balancing Chemical Equations: placing a coefficient before each reactant and product so that the # of atoms is equal on both sides! Reactants: Left of equation (react together) Product: Right of equation (result of reaction) Rules for balancing: 1 Count the number of atoms on both sides to see what is missing!!! The number of each atom stays the same before and after the reaction. 2 The type of atoms must stay the same before and after the reaction (you cannot add new atoms or remove any) 3 The mass of the atoms stays the same before and after the reaction. 4 Only change the coefficients when balancing (must be whole numbers, must be as small as possible!! SIMPLIFY) 5 DO NOT TOUCH THE SUBSCRIPTS OF ANY ATOMS!!! CHECK by counting atoms on both sides to make sure they are equal!!! What is incorrect with the following equation? Al + O 2 Al 2 O 3 5

6 Balancing equations 1. 4 P + 5 O 2 P 2 O 5 2. H 2 + O 2 H 2 O 3. P + Cl 2 PCl 3 4. P + O 2 P 2 O 5 5. N 2 + O 2 N 2 O 5 6. Fe 2 O CO 2 Fe + CO KOH + H 2 SO 4 K 2 SO 4 + H 2 O 8. NH 3 + Cl 2 HCl + N 2 9. NaOH Na + O 2 + H 2 O 10. FeS + O 2 Fe 2 O 3 + SO HCl + Fe FeCl 2 + H Na + H 2 O NaOH + H H 2 SO 4 + S SO 2 + H 2 O 14. C 8 H 18 + O 2 CO 2 + H 2 O 15. HNO 3 + H 2 NH 3 + H 2 O 16. FeCl 3 + NH 4 OH Fe(OH) 3 + NH 4 Cl 17. H 2 SO 4 + C CO 2 + H 2 O + SO 2 6

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12 Mass of Equations 1. You combined 80 g of 2 KOH with 100 g of H 2 SO 4 to produce 120 g of K 2 SO 4 and 2 H 2 O. How much water was produced? 2. You combined 160 g of 2 H 2 with O 2 and produced 197 g of 2 H 2 O. How much O 2 was produced? 3. You combined 25 g of C 3 H 8 with 5 O 2 to produce 37 g of 3 CO 2 and 30 g of 4 H 2 O. How much O 2 was produced? 12

13 Past Exam Questions 1. One litre of nitrogen (N 2 ) reacts with three litres of hydrogen (H 2 ) to produce two litres of ammonia, according to the following equation : N 2(g) + 3 H 2(g) 2 NH 3(g) Which of the following models best describes the chemical change that occurs? 2. Which of the following chemical equations are correctly balanced? 1. 4 Bi (s) + 3 O 2(g) 2 Bi 2 O 3(s) 2. 2 Bi (s) + Cl 2(g) 2 BiCl 3(s) 3. 2 Bi 2 S 3(s) + 9 O 2(g) 2 BiO 3(s) + 6 SO 2(g) 4. Bi 2 O 3(s) + 3 C (s) 2 Bi (s) + 3 CO (g) 5. As 2 O 3(s) + 6 H 2(g) 2 AsH 3(s) + 3 H 2 O (g) A) 1, 3 and 4 C) 3, 4 and 5 B) 1, 4 and 5 D) 2 and 3 3. One of the causes of acid rain is the sulfur released when fossil fuels such as coal and oil are burned. The following two reactions take place when these fuels are burned: sulfur dioxide + oxygen sulfur trioxide sulfur trioxide + water sulfuric acid With the above reactions in mind, a student combined 128 g of sulfur dioxide with 32 g of oxygen to produce sulfur trioxide. He then combined all the resulting sulfur trioxide with 36 g of water to produce sulfuric acid. What mass of sulfuric acid did he produce? 4. The Iron and Steel Company uses a chemical reaction to transform ferric oxide (rust) into iron. The balanced equation for this reaction is as follows: 2 Fe 2 O 3(s) + 3 C (s) + energy 4 Fe (s) + 3 CO 2(g) To determine how much CO 2 it emits, the company took a sample and obtained the data presented in the table below Masses of the four Substances before and after the reaction Using the law of conservation of matter, calculate the mass of CO 2 emitted during this reaction. 13

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