P2

• Factors Affecting Rates of Reaction

  • Temperature
  • Concentration
  • Surface Area
  • Catalysts
• Temperature


  • Increasing the temperature from 20°C to 30°C can significantly increase the rate of reaction
• Concentration


  • In a reaction between hydrochloric acid and magnesium, increasing the concentration of HCl will increase the rate at which magnesium dissolves
• Surface Area


  • Powdered calcium carbonate reacts faster with hydrochloric acid than large marble chips
• Catalysts


  • The use of manganese dioxide (MnO₂) as a catalyst in the decomposition of hydrogen peroxide (H₂O₂) into water and oxygen
• Collision Theory


  Chemical reactions occur when particles collide with sufficient energy and the correct orientation. Only a fraction of collisions result in a reaction; these are called effective collisions
• Activation Energy (Ea)


  The minimum energy required for particles to react upon collision. Reactions with lower activation energy proceed faster as more particles have sufficient energy to react. Catalysts lower the activation energy, increasing the reaction rate
• Methods to Measure Rate

  • Gas Collection
  • Mass Loss
  • Color Change
  • Turbidity Change
• Calculating Rate of Reaction

  Rate of reaction = change in concentration (or volume or mass) / time. Units: Typically, mol/L/s (moles per liter per second) for concentration, or cm³/s for gas volume
• Required Practical 5: Investigating the Effect of Concentration on Reaction Rate

  1. Measure 50 cm³ of hydrochloric acid into a conical flask

  2. Add a strip of magnesium ribbon to the acid and start the stopwatch

  3. Record the time taken for the magnesium to completely react and disappear

  4. Repeat the experiment with different concentrations of hydrochloric acid
• Variables in Required Practical 5

  • Independent: Concentration of hydrochloric acid
  • Dependent: Time taken for the reaction to complete
  • Control: Temperature, length and mass of magnesium ribbon, volume of acid
• Alkanes


  Saturated hydrocarbons (single bonds only). General formula: C_nH_{2n+2}. Examples: Methane (CH₄), Ethane (C₂H₆), Propane (C₃H₈), Butane (C₄H₁₀). Properties: Generally unreactive, but undergo combustion and substitution reactions
• Alkenes


  Unsaturated hydrocarbons (contain at least one C=C double bond). General formula: C_nH_{2n}. Examples: Ethene (C₂H₄), Propene (C₃H₆), Butene (C₄H₈). Properties: More reactive than alkanes, undergo addition reactions (e.g., with bromine water, hydrogen)
• Crude Oil


  A mixture of hydrocarbons of varying lengths. Formed from the remains of marine organisms over millions of years under heat and pressure
• Fractional Distillation


  1. Crude oil is heated to vaporize hydrocarbons

  2. Vapors enter a fractionating column where temperature decreases from bottom to top

  3. Hydrocarbons condense at different levels depending on their boiling points

  4. Fractions: Gases (e.g., propane, butane), Petrol (gasoline), Naphtha, Kerosene (paraffin), Diesel, Fuel oil, Lubricating oils, Bitumen
• Catalytic Cracking


  Uses a catalyst (e.g., zeolite) at about 500°C. Converts long-chain alkanes into shorter alkanes and alkenes
• Steam Cracking


  Uses high temperature (about 800°C) without a catalyst. Produces a mixture of alkenes and shorter alkanes
• Addition Polymers


  Formed from monomers with double bonds (alkenes). Examples: Polyethene (from ethene), Polypropene (from propene). Properties depend on the monomers used and the conditions of polymerization
• Condensation Polymers


  Formed from monomers with two different functional groups. Examples: Polyesters (from dicarboxylic acids and diols), Polyamides (from dicarboxylic acids and diamines). Involve the elimination of a small molecule (e.g., water or HCl) during polymerization
• Required Practical 6: Identifying Ions using Chemical Tests


  1. Flame Tests: Test for metal cations by observing the color of the flame

  2. Precipitation Reactions: Add sodium hydroxide to solutions of different metal ions, observe the color of the precipitate formed

  3. Test for Anions: Carbonates, Sulfates, Halides
• Pure Substances


  Consist of a single element or compound. Have a specific melting and boiling point. Example: Distilled water, pure gold
• Mixtures


  Consist of two or more substances physically combined. Properties are a combination of the individual components. Example: Air, saltwater
• Paper Chromatography


  1. A spot of the sample is placed on the baseline of chromatography paper

  2. The paper is placed in a solvent (mobile phase) that travels up the paper by capillary action

  3. Different components travel at different rates and separate

  4. Rf Value: R_f = distance traveled by substance / distance traveled by solvent
• Hydrogen Test


  Light a splint and place it near the gas. A 'squeaky pop' sound confirms the presence of hydrogen. Reaction: 2H_2 + O_2 → 2H_2O
• Oxygen Test


  Insert a glowing splint into the gas. The splint will relight in the presence of oxygen. Reaction: 2H_2O_2 → 2H_2O + O_2 (decomposition of hydrogen peroxide)
• Carbon Dioxide Test


  Bubble the gas through limewater (calcium hydroxide solution). It turns milky if carbon dioxide is present. Reaction: CO_2 + Ca(OH)_2 → CaCO_3 + H_2O
• Chlorine Test


  Hold damp litmus paper in the gas. The paper will bleach white in the presence of chlorine. Reaction: Cl_2 + H_2O → HCl + HOCl (chlorine reacts with water to form hydrochloric acid and hypochlorous acid)
• Early Atmosphere


  Dominated by volcanic activity. Main gases: Carbon dioxide, water vapor, ammonia, and methane
• Changes Over Time in the Atmosphere

  1. As the Earth cooled, water vapor condensed to form oceans

  2. Carbon dioxide dissolved in oceans, forming carbonates

  3. Photosynthetic organisms (cyanobacteria) evolved, producing oxygen

  4. Oxygen levels increased, leading to the formation of the ozone layer, which allowed for the development of more complex life forms
• Greenhouse Gases


  Include carbon dioxide (CO₂), methane (CH₄), and water vapor (H₂O). Trap heat in the Earth's atmosphere, maintaining a temperature suitable for life
• Human activities, such as burning fossil fuels and deforestation


  Increase greenhouse gas levels, leading to climate change effects like global warming, rising sea levels, extreme weather events, and changes in ecosystems
• Atmospheric Pollutants


  • Carbon Monoxide (CO)
  • Sulfur Dioxide (SO₂)
  • Nitrogen Oxides (NOx)
  • Particulates
• Carbon Monoxide (CO)


  Produced by incomplete combustion of fossil fuels. Toxic, prevents oxygen transport in the blood
• Sulfur Dioxide (SO₂)


  Produced by burning fossil fuels containing sulfur. Causes acid rain
• Nitrogen Oxides (NOx)


  Produced by high-temperature combustion. Contributes to smog and acid rain
• Particulates


  Tiny solid particles from burning fossil fuels. Cause respiratory problems and contribute to global dimming