Stoichiometry, Solutions, Kinetics, and Chemical Equilibrium
Stoichiometry is the field of chemistry that studies the relationships between the quantities involved in a chemical reaction. The laws governing stoichiometry are:
- Law of definite proportions: when you combine two or more elements for a given compound, they always do so with a relationship of constant mass.
- Law of constant composition: All chemical elements in a pure state always contain the same elements.
- Law of conservation of mass: Matter is not created or destroyed, only transformed.
Stoichiometry is determined by:
- Limiting reagent: The reactant that determines the amount of product obtained in a chemical reaction.
- Reaction yield: The amount of product produced in a chemical reaction.
Solutions are homogeneous mixtures of a solute in a solvent.
- Solute: The substance dissolved.
- Solvent: The substance that dissolves the solute.
Types of solutions:
- Diluted: A solution with a small amount of solute relative to the solvent.
- Saturated: A solution with the maximum amount of solute that can dissolve at a given temperature.
- Supersaturated: A solution that contains more solute than it can normally dissolve at a given temperature.
Solubility: The maximum amount of solute that can dissolve in a given amount of solvent at a given temperature.
Factors affecting solubility:
- Contact Surface: The solute-solvent interaction increases with more surface contact, leading to faster dissolution (e.g., spraying the solute).
- Agitation: Shaking the solution helps separate layers and form new solute-solvent interactions, continuing dissolution.
- Temperature: Increasing the temperature favors molecular movement, increasing the energy of solid particles and allowing them to dissolve more easily.
- Pressure: This primarily affects the solubility of gases, with solubility being directly proportional to pressure.
Concentration: The amount of solute in a solution.
Classified as:
Quantitative:
- Physical Units: % P/P, % P/V, % V/V
- Chemical Units: Molality, Molarity, Normality, Molar fraction
Colligative properties of solutions are properties that depend on the number of solute particles in a given amount of solvent.
- Vapor Pressure: Raoult’s Law states that the decrease in vapor pressure of the solvent is proportional to the mole fraction of solute.
- Boiling Point: The temperature at which the vapor pressure equals the applied pressure (usually atmospheric pressure).
- Freezing Point: The temperature at which the vapor pressure of liquid and solid are equal. Solutions freeze at a lower temperature than the pure solvent.
- Osmotic Pressure: The pressure required to prevent the flow of solvent across a semipermeable membrane from a region of lower solute concentration to a region of higher solute concentration.
Chemical Kinetics is the branch of chemistry that studies the rates of chemical reactions and the factors that affect them.
Rate of chemical reaction: The change in concentration of reactants or products per unit time. Factors affecting reaction rate:
- Nature of the reactants: The inherent properties of the reactants, such as their chemical bonds and molecular structure, influence the reaction rate.
- Concentration of the reactants: Increasing the concentration of reactants generally increases the reaction rate.
- Temperature: Increasing the temperature generally increases the reaction rate due to increased kinetic energy of molecules.
- Catalysis: Catalysts speed up reactions by providing an alternative reaction pathway with a lower activation energy.
Chemical Equilibrium is a state where the rates of the forward and reverse reactions are equal, resulting in no net change in concentrations of reactants and products.
Types of reactions:
- Direct (Irreversible) Reaction: Reactions that proceed in one direction until one or more reactants are exhausted.
- Reverse (Reversible) Reaction: Reactions that can proceed in both forward and reverse directions, potentially reaching a state of equilibrium.
External factors affecting chemical equilibrium:
- Adding or removing a chemical species: Adding a component favors the reaction that consumes it; removing a component favors the reaction that produces it.
- Changing concentration: The law of mass action states that the rate of a chemical reaction is proportional to the product of the molar concentrations of the reactants.
- Changing temperature: Increasing temperature favors endothermic reactions; decreasing temperature favors exothermic reactions.
- Changing pressure: Increasing pressure favors the reaction that produces fewer moles of gas; decreasing pressure favors the reaction that produces more moles of gas.
- Adding a catalyst: Catalysts do not affect the equilibrium position, but they do speed up the attainment of equilibrium.