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HSC Chemistry

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  1. Module 1: Properties and Structure of Matter
    1.1 Properties of Matter
  2. 1.2 Atomic Structure and Atomic Mass
  3. 1.3 Periodicity
  4. 1.4 Bonding
  5. Module 2: Introduction to Quantitative Chemistry
    2.1 Chemical Reactions and Stoichiometry
  6. 2.2 Mole Concept
  7. 2.3 Concentration and Molarity
  8. 2.4 Gas Laws
  9. Module 3: Reactive Chemistry
    3.1 Chemical Reactions
  10. 3.2 Predicting Reactions of Metals
  11. 3.3 Rates of Reactions
  12. Module 4: Drivers of Reactions
    4.1 Energy Changes in Chemical Reactions
  13. 4.2 Enthalpy and Hess's Law
  14. 4.3 Entropy and Gibbs Free Energy
  15. Module 5: Equilibrium and Acid Reactions
    5.1 Static and Dynamic Equilibrium
    5 Topics
  16. 5.2 Factors that Affect Equilibrium
    2 Topics
  17. 5.3 Calculating the Equilibrium Constant
    2 Topics
  18. 5.4 Solution Equilibria
  19. Module 6: Acid/Base Reactions
    6.1 Properties of Acids and Bases
    7 Topics
  20. 6.2 Using Brønsted–Lowry Theory
    2 Topics
  21. 6.3 Quantitative Analysis
    1 Topic
  22. Module 7: Organic Chemistry
    7.1 Nomenclature
    2 Topics
  23. 7.2 Hydrocarbons
    2 Topics
  24. 7.3 Products of Reactions Involving Hydrocarbons
  25. 7.4 Alcohols
    1 Topic
  26. 7.5 Reactions of Organic Acids and Bases
  27. 7.6 Polymers
    2 Topics
  28. Module 8: Applying Chemical Ideas
    8.1 Analysis of Inorganic Substances
    3 Topics
  29. 8.2 Analysis of Organic Substances
  30. 8.3 Chemical Synthesis and Design
  31. Working Scientifically
    Working Scientifically Overview
    1 Topic
Lesson 15, Topic 3
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Non-Equilibrium Systems

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Combustion

When hydrocarbons undergo complete combustion in an excess of oxygen, carbon dioxide and water are formed. These reactions are strongly exothermic:

\text{CH}_4 (g) + 2\text O_2 (g) \rightarrow \text{CO}_2 (g) + 2\text H_2 \text O (l)

The release of heat energy in this exothermic reaction drives the reaction in the forward direction. This reaction is spontaneous as the Gibbs free energy change is negative. (ΔG < 0).

The high activation energy for the reverse reaction reduces the chance that products will recombine to form reactants. Also, as combustion reactions occur in open systems, the products can escape into the surroundings and therefore cannot recombine to produce reactant molecules.

Photosynthesis

Photosynthesis occurs in the chloroplasts of green plant cells. Solar energy is absorbed by chlorophyll molecules inside the chloroplasts.

Chlorophyll selectively absorbs red and violet light in the visible spectrum. This energy is used to convert carbon dioxide and water into glucose and oxygen, as seen below:

6\text{CO}_2 (g) + 6\text H_2 \text O (l) \rightarrow \text C_6 \text H_{12} \text O_6  (s) + 6 \text O_2 (g)

The Gibbs free energy change for photosynthesis is positive (ΔG > 0) and therefore the reaction is non-spontaneous. This reaction requires solar energy to occur.

The reaction products are lost from the system and this prevents the reverse reaction from ocurring.