Chemical Reactions and Equation-2

• Chemical Equations


  The representation of a chemical change in terms of symbols and formulae of the reactants and products
• Chemical Formulae


  A substance's chemical formula is a symbolic representation of the number of atoms present in a single molecule of that material
• Steps for writing Chemical Equation

  1. Step I: Writing skeletal Equation

  2. Step II: Balancing of Chemical Equation
• Chemical change

  • Cooking of food
  • Rusting of iron
  • Heating of Lead nitrate
  • Souring of milk
  • Ripening of fruit
• Endothermic Reactions


  A chemical reaction that involves the absorption of heat energy
• Exothermic Reaction

  A chemical process that results in the release of heat energy
• Chemical change


  A change that results in the formation of one or more new compounds. Also known as chemical reactions
• Chemical change

  • New substances are produced during a chemical reaction
  • Changes in energy are involved
  • During the reaction, there occurs a change in mass
  • There is a permanent alteration
• Exothermic Reaction

  • C + O2 → CO2 + 393.5 kJ
  • 2N2 + 3H2 → 2NH3 + 92.3 kJ
• Chemical Equations

  • KMnO4 + HCl → KCl + MnCl2 + H2O + Cl2
• Rusting of iron

  • A new substance, iron oxide, is created as iron rusts
  • The modification is permanent
  • When rust forms, the mass of the object increases
  • A shift in energy has occurred
• Chemical Formulae

  • One water molecule has the formula H2O
  • One molecule of sulphuric acid has the formula H2SO4
• A balanced chemical equation is one in which the number of atoms of each element is equal on both sides of the equation
• Endothermic Reactions

  • N2 + O2 → 2NO + 180.5 kJ
  • 2HgO → 2Hg + O2 + 180 kJ
• Limitation of a Chemical Equation: The condition of the chemicals is not mentioned. As a result, symbols like (s) for solid, (l) for liquid, (aq) for dissolved in water, (g) for gas, and (vap) for vapor should be added. It does not reveal if the reaction is finished, the reaction time or speed, substance concentrations, temperature, humidity, pressure, catalyst, or other environmental factors. Changes in color have to be mentioned separately
• The Hit and Trial approach is a technique for balancing chemical equations
• From a chemical equation we can conclude various reactants and products' names, reactant and product formulae, the number of moles of the reactants and products in relation to each other, masses of reactants and products relative to each other, volumes of gaseous reactants and products in relation to each other
• Balancing of Chemical Equation

  A balanced chemical equation is one in which the number of atoms of each element is equal on both sides of the equation. Equations must be balanced at all times. The amount of hydrogens on both sides should be an even number whenever H2O is present on one side. If there are 4 hydrogen atoms, then 8 hydrogen atoms are present. If there are 7 hydrogen atoms, then 14 hydrogen atoms, indicating that all the numbers are even. There must be an even number in front of HCl on the reactant side. As a result, there will be an even amount of chlorine atoms. However, the quantity of chlorine atoms in the product is unusual. Let's alter it to the simplest even number we can think of, which is 2. Since the number of K atoms in 2 KCl = 2, we have to put 2 in front of KMnO4 for balancing K atoms. In 2 KMnO4, there are 2 K, 2 Mn, and 8 O. So, add these numbers in front of K, Mn, and O. If there are 8 H2O on the product side, there should be 16 H (8 x 2) on the reactants side as well. Now the only unbalanced one is Chlorine. On the left-hand side, there are 16 Cl. On the right-hand side, there are 2 Cl in 2 KCl + 4 Cl in 2 MnCl2, making a total of 6(2 + 4). So, 10 more Cl atoms are to be accounted for. Place 5 in front of 2 Cl2 to make it 10 (5 x 2)
• Electrolysis is the process of decomposing a substance by putting an electric current through it
• Types of Combination reactions

  • Burning of hydrogen in air or oxygen to produce water
  • Burning of carbon monoxide in oxygen to form carbon dioxide
  • Combination of ammonia and hydrogen chloride to produce ammonium chloride
• Chemical Equations-Based Calculations

  • A chemical reaction can provide quantitative data and calculate the number of moles of reactants and products
• Some reactions are reversible and are represented by ⇌ or ⇆
• Mercuric oxide, when heated, undergoes thermal decomposition, to give mercury and oxygen
• Types of Reactions

  • Combination or Synthesis Reactions: The reactions in which two or more chemicals combine to generate a single new compound
  • Decomposition reactions: A complex is broken down into two or more simple components using heat or electricity
• Steps involved in balancing a Chemical Equation


  1. Step 1: Write the skeleton equation correctly

  2. Step 2: Start with the compound that has the maximum atoms or maximum types of atoms and the atoms present in it are balanced first

  3. Step 3: Start by balancing elements that only appear once on each side of the arrow. Then, on each side, balance elements that appear more than once

  4. Step 4: The Elementary substances are balanced last

  5. Step 5: To make all the coefficients whole numbers, the entire equation is multiplied by a suitable number if necessary
• Decomposition reactions

  Decomposition reactions occur when a complex is broken down into two or more simple components using heat or electricity
• Photolysis: The decomposition of a compound with light is called photolysis
• A balanced ionic equation must fulfil both mass and charge balance
• Heating blue copper nitrate crystals causes thermal breakdown, resulting in black copper oxide, reddish brown nitrogen dioxide fumes, and a colourless oxygen gas
• Thermal decomposition

  • Heating blue copper nitrate crystals causes thermal breakdown, resulting in black copper oxide, reddish brown nitrogen dioxide fumes, and colorless oxygen gas
• Electrolytic decomposition


  When molten lead bromide is exposed to an electric charge, it decomposes into lead and bromine
• A substitution or displacement reaction occurs when the atoms of one element replace the atoms of another element in a compound's molecules
• Double Displacement Reactions / Metathesis reactions

  • ZnSO4 + BaCl2 → ZnCl2 + BaSO4
• Double Displacement Reactions / Metathesis reactions

  • NaCl + AgNO3 → NaNO3 + AgCl
• Electrolytic Decomposition

  When water is acidified with a little amount of sulfuric acid and a direct current is run through it, electrolytic breakdown occurs, resulting in hydrogen and oxygen
• Activity Series: The metal activity series is a list of metals arranged in decreasing chemical activity order
• Double Displacement Reactions / Metathesis reactions


  • The mutual exchange of ions in which two chemicals react to generate two distinct molecules
• Double Displacement Reactions / Metathesis reactions

  • 2HCl + Pb(NO3)2 → 2HNO3 + PbCl2
• A precipitate is the insoluble substance that forms
• Neutralization


  A form of double displacement reaction in which the reactants are a base and an acid, and the products are salt and water