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Understanding Reversible Reactions and Vapor Pressure in Chemistry

This chapter delves into the concept of reversible reactions, illustrating that most chemical processes can go in either direction depending on conditions. It explores the dynamic equilibrium between evaporation and condensation, demonstrated with water (H2O) as an example. The relationship between vapor pressure and the rate of evaporation for substances like ethanol is also presented. Distinctions between intramolecular and intermolecular forces are elucidated, emphasizing the role of attractive forces in molecular interactions.

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Understanding Reversible Reactions and Vapor Pressure in Chemistry

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  1. Chapter 17 Part 2

  2. Saharan Desert

  3. Saharan Oasis

  4. Sahara was once fertile grasslands

  5. Reversible Reactions • Most chemical reactions are reversible. • Depending on conditions.

  6. H2O(l)  H2O(g) • Evaporation and condensation are reversible processes. • An equilibrium occurs when two opposing processes occur at the same rate.

  7. EquilibriumH2O(l)  H2O(g)

  8. H2O(l)  H2O(g) • Evaporation and condensation are reversible processes. • An equilibrium occurs when two opposing processes occur at the same rate. • At equilibrium the concentrations of the substances involved in the reaction will remain constant. • [ ] = concentration.

  9. EquilibriumH2O(l)  H2O(g)

  10. Vapor Pressure • Suppose we conduct an experiment in which we place a quantity of ethanol (C2H5OH) in an evacuated, closed container (a). • The ethanol will quickly begin to evaporate. • The pressure exerted by the vapor will begin to increase. • After a short time the pressure will attain a constant value, called the vapor pressure of ethanol (b).

  11. Vapor Pressure • At any given temperature, for a particular substance, there is a pressure at which the gas of that substance is in equilibrium with its liquid or solid form. This is the vapor pressure of that substance at that temperature. • The equilibrium vapor pressure is an indication of a liquid's evaporation rate. • A substance with a high vapor pressure at normal temperatures has a high rate of evaporation and is often referred to as volatile.

  12. Attractive Forces Two types of attractive forces are: • Intramolecular forces • Intermolecular forces

  13. Intramolecular Forces • Intramolecular forces = attractive forces that hold particles together using ionic, covalent, or metallic bonds • Intra means “within” • Intramolecular forces = bonds

  14. Intermolecular Forces(Van der Waals forces) • Inter means “between” • Intermolecular forces are forces between molecules • Larger polar molecules have greater Van der Waals forces.

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