chemical changes

• Chemical Reaction


  When a chemical change occurs, a chemical reaction takes place
• Components of a chemical reaction


  • Reactants (starting materials)
  • Arrow (represents change)
  • Products
• Chemical reaction example


  • Carbon burns in the presence of oxygen to form carbon dioxide
• Burning charcoal is an irreversible chemical reaction

  
• Physical Change


  No formation of new compounds, reaction is reversible
• Chemical Change


  Formation of new compounds, reaction is irreversible
• Dissolving salt in water is a physical change
• Simple distillation can be used to obtain water and salt from salt solution
• Types of Interactions for Chemical Changes

  • Mixing
  • Heating
  • Oxygen
  • Light
  • Electricity
  • Neutralisation
• A chemical change can take place when reactants interact with heat, oxygen, light or are when they are mixed
• Physical Properties


  Feels soapy, tastes bitter, corrosive, pH more than 7, turns moist red litmus paper blue
• Chemical Properties


  Reacts with acids (hydrochloric, sulfuric, nitric, carbonic)
• Common Acids


  • Vinegar (acetic acid)
  • Citrus fruits (citric acid)
  • Car battery (sulfuric acid)
  • Vitamin C (ascorbic acid)
  • Gastric juice (hydrochloric acid)
  • Making fertilisers, dyes and plastics (nitric acid)
  • Carbonated drinks (carbonic acid)
• Common Alkalis


  • Soap and detergents (sodium hydroxide)
  • Bleach (potassium hydroxide)
  • Fertilisers and cleaning liquids (aqueous ammonia)
  • Baking soda (ascorbic acid)
• pH


  Scale used to measure how acidic or alkaline a solution is, values range from 0 to 14

  
• Acidic

  pH values less than 7
• Neutral

  pH value equal to 7
• Alkaline

  pH values more than 7
• Indicators


  Substances used to find out whether a solution is acidic or alkaline, change colour in acidic, neutral or alkaline solutions

  
• Litmus paper


  • Red in acidic solution, blue in alkaline solution

  
• Universal Indicator

  • Provides an approximate pH value indicated by the respective colour observed
• Universal Indicator is a better indicator than litmus paper
• A pH meter is a laboratory instrument that enables us to accurately determine pH values of solutions
• Different indicators have their own colour ranges, there are many natural pH indicators
• Word Equation

  Reactants and products represented by words
• Chemical Equation

  Reactants and products represented by chemical formula
• Evidence that a chemical change has occurred: properties of reactants are completely different from properties of products, atoms of reactants are rearranged to form new substances
• Copper(II) carbonate decomposition


  1. Copper(II) carbonate

  2. Heat

  3. Copper(II) oxide

  4. Carbon dioxide
• Acid reacts with metals

  To produce salt and hydrogen gas
• Acid reacts with metal carbonates

  To produce salt, carbon dioxide and water
• Acid reacts with alkalis


  To produce salt and water (neutralisation reaction)
• The name of the reaction between acid and alkali is called a neutralisation reaction
• Writing word equations for acid reactions

  Reactant 1 + Reactant 2 → Product 1 + Product 2
• Acid reactions


  • Hydrochloric acid + Zinc → Zinc chloride + Hydrogen

  Sulfuric acid + Magnesium → Magnesium sulfate + Hydrogen

  Nitric acid + Potassium → Potassium nitrate + Hydrogen

  Hydrochloric acid + Sodium hydroxide → Sodium chloride + Water

  Sulfuric acid + Calcium hydroxide → Calcium sulfate + Water

  Nitric acid + Ammonia → Ammonium nitrate + Water
• When a solid is added to an acid, a gas is produced
• To identify the gas, bring it to a lighted splint (hydrogen test) or bubble it into limewater (carbon dioxide test)
• Balanced Chemical Equation

  Chemical equation where the number of atoms of each element is the same on both sides, following the law of conservation of mass
• Applications of Chemical Changes

  • Cooking (softens food, makes nutrients more absorbable)

  Respiration (releases energy for survival and reproduction)

  Decay (breaks down organic matter, returns nutrients to environment)

  Rusting (iron reacts with water and oxygen, can be reduced by painting, oiling, galvanizing, drying)

  Combustion (produces energy and air pollutants like carbon monoxide, sulfur dioxide, nitrogen oxides)
• The ocean is the largest carbon sink, carbon dioxide dissolves in seawater to produce carbonic acid, decreasing the pH of the ocean (ocean acidification)
• In a chemical reaction, atoms are rearranged to form new substances with different properties.