Determining Chemical Reactions

• A chemical reaction takes place when the nature and identity of a substance changes

Activity 1.1: Burning Magnesium Ribbon

• Magnesium ribbon needs to be cleaned with sandpaper
• It is held with tongs and burned using a spirit lamp or burner
• Burning magnesium ribbon produces a dazzling white flame
• It turns into a white powder called magnesium oxide
• Magnesium oxide results from the reaction between magnesium and oxygen in the air

Activity 1.2: Reaction of Lead Nitrate and Potassium Iodide

• Lead nitrate solution is mixed with potassium iodide solution
• A change is observed

Activity 1.3: Reaction of Zinc Granules and Acid

• A few zinc granules react with dilute hydrochloric acid or sulphuric acid
• Precautions should be taken when handling acid
• Any changes happening around the zinc granules?
• Check the temperature of the conical flask or test tube

Determining Chemical Reactions

• Any one of the following shows that a chemical reaction has taken place:
• A change in state
• A change in color
• Production of a gas
• A change in temperature

Chemical Equations

Describing Reactions

• Activity 1.1 can be shortened to: a Magnesium ribbon, when burnt in oxygen, converts to Magnesium oxide
• The easiest way is to write it using a word equation
• Magnesium + Oxygen -> Magnesium oxide

Reactants and Products

• Reactants such as magnesium and oxygen, undergo a chemical change
• Products, like magnesium oxide, are formed during the reaction
• A word equation shows the change of reactants into products
• Reactants are written on the left-hand side (LHS) with a plus sign (+)
• Products are on the right-hand side (RHS) with a plus sign (+)
• The arrowhead shows the reaction's direction

Writing a Chemical Equation

• Chemical formulas are more concise than words for representing chemical equations
• A chemical equation represents a chemical reaction
• Mg + O2 -> MgO is the chemical equation for the reaction of magnesium and oxygen

Balanced Equations

• Count and compare the number of atoms of each element on both sides of the arrow
• If balanced, the number of atoms of each element is equal on both sides
• An unbalanced equation means mass is not the same on both sides
• Such equations are called skeletal chemical equations
• Eq. (1.2) is a skeletal chemical equation for the burning of magnesium in air

Balancing Chemical Equations

• Mass cannot be created or destroyed in a chemical reaction
• The total mass of elements in the reactants must equal the total mass in the products
• The number of atoms of each element must remain the same before and after the reaction
• Skeletal chemical equations must therefore be balanced

Balancing Steps using activity 1.3 as example

• The word equation for activity 1.3 is Zinc + Sulphuric acid -> Zinc sulphate + Hydrogen
• The chemical equation is Zn + H2SO4 -> ZnSO4 + H2
• This equation is balanced because the number of atoms of each element is the same on both sides of the arrow
• Let us balance equation Fe + H2O -> Fe3O4 + H2
• Step I: Fe + H2O -> Fe3O4 + H2 (draw boxes)
• Step II: List the number of atoms of each element
• Fe: Reactants (1), Products (3)
• H: Reactants (2), Products (2)
• O: Reactants (1), Products (4)
• Step III: Balance the oxygen atoms
• There are four oxygen atoms on the RHS and only one on the LHS
• You cannot alter the formulae
• Fe + 4 H2O -> Fe3O4 + H2 -Step IV: Balance hydrogen atoms
• The number of hydrogen atoms have been made four on the RHS
• Fe + 4 H2O -> Fe3O4 + 4 H2
• Step V: Only one element left, namely iron
• Atoms of iron
• Initial Reactants (1), Products (3)
• To balance multiple Reactants by three to equal 3
• 3Fe + 4 H2O -> Fe3O4 + 4 H2
• Step VI: Check by counting each element on both sides of the equation is equal
• Step VII: the equation is now balanced. This method is called hit-and-trial

Physical States

• Symbols of physical states can make a chemical equation more informative
• The states are:
• gas (g)
• liquid (l)
• aqueous (aq)
• solid (s)
• 3Fe(s) + 4H2O(g) -> Fe3O4(s) + 4H2(g)
• Sometimes the symbol (g) is used with H2O which is to indicate steam
• Reaction conditions such as tmperature, pressure cataluysts are indicated above or below the arrow

1.2: Types of Chemical Reactions

• Chemical reactions involve the breaking and making of bonds between atoms to produce new substances

1.2.1: Combination Reaction

• Activity 1.4: Take a small amount of calium oxide, slowly add water, any any changes in temperature are observed
• The Calcium oxide reacts vigorously with water to produce slaked lime (calium hydroxide) releasing a large aount of heat.
• CaO(s) + H2O(l) -> Ca(OH)2(aq) + Heat
• A reaction when a single product is formed from two or more reactants is known as a combination reaction

Solution of Slaked lime

• Used for whitewashing walls
• Calcium hydroxide reacts slowly with the crabon dioxide in air to form a thin layer of calcium carbonate on the walls
• Marble is CaCO3
• Ca(OH)2(aq) + CO2(g) -> CaCO3(s) + H2O(l)

Examples of combination reactions

1. Burning Coal

• C(s) + O2(g) -> CO2(g)

2. Formation of water

• 2H2(g) + O2(g) -> 2H20(l)
• Reactions which heat is release with the formation of products are exothermic chemical reactions

Other Examples of Exothermic reaction

1. Burning natural gas (respiration)

• CH4(g) + 2O2(g) -> CO2(g) + 2H2O(g)

2. In our bodies, food is broken down into simpler substance by the oxygen.
3. The decomposition of vegetable matter into compost is also an example of exothermic reactions

1.2.2: Decomposition Reaction

• The Boiling tube needs to Waft and point the mouth of the Boiling tube away from self
• Have you noticed the green colour change?
• You can smell the characteristic odour

1. 2FeSO4(s) -> Fe2O3(s) + SO2(g) + SO3(g)

• Decomposition reaction is the breakingdown of a single reaction to give simplier products
• Ferrous sulpahte (FeSO4 . 7H20) lose water and then decomposes to Ferric acid, Sulphur and Sulphur trioxide
• The Decomposition of calcium carbonate to calcium oxide and crabon dioxide is an important dcomposition reaction -CaCO3(s) -> CaO(s) + CO2(g)
• Called the Quick Lime
• Reactions that is carried out by heating, it is called thermal decomposition

1.2.3: Displacement Reaction

• Activity 1.9- Take three Nails and clean by sanding paper
• Two test tubes marked A and B taking copper Sulphate solution
• and tie iron nails with string and immerse into test tube
• The following chemical reaction example takes in the activity
• Fe(s) + CuSO4(aq) -> FeSO4(aq) + Cu(s)
• Iron has displaces or removed another element, Copper to form as displacement reaction
• Example -Zn(s) + CuSO4(aq) -> ZnSO4(aq) + Cu(s)
• Lead is more reactive than copper, and displaces it

1.2.4: Double Displacement Reaction

• Activity 1.10
• Take 3ML if sodium and Barium solution in solution, and mix both
• Na2SO4(aq) + BariumCl2(aq) -> BaSO4(s) + 2Nacl(aq)
• There with be the White susbtance, so they can be called precipitate

1.2.5: Oxidation and Reduction

• The following Reaction is oxidation
• 2Cu + O2 -> 2Cuo
• If Hydrogen gas is passsed over by this oxide, then the Black coating turns Brown as the reverse reaction -CuO + H2 -> Cu + H2o
• If a substance gains oxygen during a reaction, its said to be oxidised, and the lessing of oxygen, its said to be reduce
• One substance reduced and oxidise is redox reaction
• Cuo + H2 -> Cu + H2o
• Some other exams are -ZnO + C -> Zn + Co
• Mno2 + 4Hcl -> MncL2 + 2H2o + Cl2

1.3 Observed effect

• Metals gets Coated with oxide and silver in moisture environment
• We can prevent some type of oxisation called rancidity and use of anti oxidants
• or store in air tight containers to prevent chips manuafactures