Unit B - Chemistry Notes

Products of Combustion Reactions

• Combustion Reactions
  • The term "combustion" translates to "to burn".
  • Examples of combustion reactions include:
  • Cellular Respiration:
    • Chemical reaction: ext{glucose} + ext{oxygen}
      ightarrow ext{carbon dioxide} + ext{water}.
  • Burning Fossil Fuels:
    • Example 1: Burning gasoline in car engines.
    • Example 2: Burning natural gas in furnaces.

Characteristics of Combustion Reactions

• Common features of combustion reactions:
  • Reactants:
  • A fuel (typically a hydrocarbon containing both carbon and hydrogen).
  • Oxygen (O2), which is essential for burning.
  • Products:
  • Carbon dioxide (CO2)
  • Water vapour (H2O)
  • Energy Transfer:
  • All combustion reactions are exothermic, releasing energy, usually in the form of heat.

Chemical Equations for Combustion

• General form of combustion reactions:
  • ext{CxHy} + ext{O}2(g) ightarrow ext{CO}2(g) + ext{H}_2 ext{O}(g)
  • where CxHy represents a hydrocarbon and O2 is oxygen.

Balancing Combustion Equations

• Balancing Tips:
  • Balance oxygen (O2) last, since it appears multiple times in the equation.
  • If there isn’t a whole number for O2 when balancing, double all other coefficients and try again.

Practice Problems: Balancing Equations

• Example Equations:
  1. ext{CH}4(g) + ext{O}2(g)
     ightarrow ext{CO}2(g) + ext{H}2 ext{O}(g)
  2. ext{C}6 ext{H}{12} ext{O}6(g) + ext{O}2(g)
     ightarrow ext{CO}2(g) + ext{H}2 ext{O}(g)
  3. ext{C}3 ext{H}8(g) + ext{O}2(g) ightarrow ext{CO}2(g) + ext{H}_2 ext{O}(g)
  4. ext{C}{25} ext{H}{52}(s) + ext{O}2(g) ightarrow ext{CO}2(g) + ext{H}_2 ext{O}(g)
  5. ext{C}2 ext{H}5 ext{OH}(l) + ext{O}2(g) ightarrow ext{CO}2(g) + ext{H}_2 ext{O}(g)
  6. ext{C}2 ext{H}6(g) + ext{O}2(g) ightarrow ext{CO}2(g) + ext{H}_2 ext{O}(g)

Common Hydrocarbons

• Important Hydrocarbons:
  • Glucose (C6H12O6) - for cellular respiration.
  • Sucrose (C12H22O11) - table sugar.
  • Methanol (CH3OH).
  • Ethanol (C2H5OH).

Types of Organic Compounds

• Alkanes:

  • Have single bonds, general formula: $ext{C}<em>n ext{H}</em>{2n+2}$.
  • Examples:
    • Methane (CH4)
    • Ethane (C2H6)
    • Propane (C3H8)

• Alkenes:

  • Have at least one double bond, general formula: $ext{C}<em>n ext{H}</em>{2n}$.
  • Examples:
    • Ethene (C2H4)
    • Propene (C3H6)

• Alkynes:

  • Have at least one triple bond, general formula: $ext{C}<em>n ext{H}</em>{2n-2}$.
  • Examples:
    • Ethyne (C2H2)
    • Propyne (C3H4)

Carbon Oxides

• Types of Carbon Oxides:
  • Carbon Dioxide (CO2)
  • Carbon Monoxide (CO):
  • Colorless, odorless, and poisonous, produced during incomplete combustion.

Natural and Man-made Sources of Carbon Oxides

• Sources:
  • Man-made: Burning carbon compounds (wood, fossil fuels).
  • Natural: Cellular respiration, forest fires, volcanic eruptions, weathering of some rocks.

The Carbon Cycle

• Recap:
  • Carbon atoms constantly cycle through the biosphere and exist in:
  • Air
  • Organisms (humans, animals)
  • Plants
  • Gases produced during combustion.

Greenhouse Effect

• Impact of Industrial Revolution:
  • Increased fossil fuel use leads to higher carbon emissions.
  • More solar radiation trapped, contributing to global warming.

Carbon Monoxide Reaction and Health Implications

• Incomplete combustion:
  • Occurs when oxygen is insufficient, resulting in CO as a product.
  • Example equation: 2 ext{CH}4(g) + 3 ext{O}2(g)
    ightarrow 2 ext{CO}(g) + 4 ext{H}_2 ext{O}(g).
• Health Risk:
  • CO binds to hemoglobin in the blood more effectively than oxygen, leading to oxygen starvation in tissues.
  • Preventative Measures:
    • Install carbon monoxide detectors in homes.

Sulfur Dioxide and Nitrogen Oxides

• Sulfur Oxides:
  • Present in fossil fuels like coal and oil and can be toxic.
• Nitrogen Oxides:
  • Form when nitrogen reacts with oxygen at high temperatures (e.g., in car engines).

Monitoring Emissions and Environmental Quality

• Purpose:
  • To understand the environmental impacts of emissions on human health and ecosystems.

Acid And Base Reactions Overview

• Acids can be defined as:
  • Solutions with $[H^+]$ concentration greater than $10^{-6}$ M (pH < 6).
• Properties of Acids:
  • Sour taste, reacts with metals, turns blue litmus red, conductive in solution.

Arrhenius Theory for Solutions

• Definition:
  • Describes dissociation of ionic compounds in water as producing ions.
  • Example: ext{NaCl}(s)
    ightarrow ext{Na}^+(aq) + ext{Cl}^-(aq).

Hydronium Ion Formation

• Hydronium Ion (H3O^+):
  • Formed when hydrogen ions interact with water, critical in identifying acidic solutions.

Brønsted-Lowry Theory**

• Concept:
  • Acids donate protons (H^+) and bases accept them.

Acid-Base Indicators

• Functional Role:
  • Indicators change color to signify solutions' pH.
• Types:
  • Litmus paper, universal indicators, and specific pH meters.

Acid Deposition

• Definition:
  • Refers to acidic compounds falling to Earth (e.g., acid rain).
  • Acids such as $ext{H}<em>2 ext{CO}</em>3$ (carbonic acid), $ext{HNO}<em>3$ (nitric acid), and $ext{H}</em>2 ext{SO}_4$ (sulfuric acid) formed from oxides.

Monitoring and Reducing Acid Deposition

• Strategies:
  • Capture pollutants before they disperse into the atmosphere through technologies.
  • Implementing stricter regulations on emissions.

Effects of Acid Deposition on Ecosystems

• Effects on Soil and Water:
  • Lowers pH, affects plant growth, leads to loss of biodiversity.

Human Impact

• Health Effects:
  • Acid rain can lead to lead and copper leaching into drinking water, causing health issues.

Summary of Key Points

• Understanding chemical reactions including combustion, acids, and bases are crucial for grasping environmental chemistry.
• Balancing chemical equations is essential for predicting and understanding reactions.
• Monitoring acid deposition impacts is vital for ecological and human health.