11.1 The Dissolution Process
3 min read•june 25, 2024
Solutions are mixtures where substances dissolve in solvents. They form when particles disperse uniformly in a , creating a . Understanding formation helps predict how different substances interact and mix.
The process involves energy changes and can be or . Factors like , , and entropy influence and spontaneity of dissolution. These concepts are crucial for understanding solution behavior in various applications.
Solution Formation and Characteristics
Formation of solutions
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- Solutions form when solutes dissolve in solvents
- : substance being dissolved, usually present in smaller amount (sugar, salt)
- : substance doing the dissolving, usually present in larger amount (water, ethanol)
- Solute particles disperse uniformly throughout the solvent
- Solute-solvent interactions replace solute-solute and solvent-solvent interactions (, dipole-dipole)
- Solutions are homogeneous mixtures
- Uniform composition and properties throughout the mixture (, color)
- No visible boundaries between components (clear liquid, no settling)
- Solutions can exist in various physical states
- (air: nitrogen, oxygen, carbon dioxide)
- (carbonated beverages: carbon dioxide in water)
- (salt water: sodium chloride in water)
- (metal : steel, brass)
Molecular properties in solution prediction
- "" principle
- dissolve in polar solvents (sugar in water)
- dissolve in nonpolar solvents (oil in hexane)
- Polarity determined by the distribution of charge within a molecule
- Polar molecules have uneven charge distribution (water, ethanol)
- Nonpolar molecules have even charge distribution (hexane, benzene)
- influence
- Hydrogen bonding, favor polar solute-solvent mixing (ethanol in water)
- favor nonpolar solute-solvent mixing (oil in hexane)
- Solubility depends on the relative strength of solute-solute, solvent-solvent, and solute-solvent interactions
- Strong solute-solvent interactions promote dissolution (salt in water)
- Strong solute-solute or solvent-solvent interactions hinder dissolution (oil in water)
Dissolution Process and Solubility
- Dissolution is the process of a solute breaking apart and mixing with a solvent
- occurs when solvent molecules surround and interact with solute particles
- is a specific type of involving water as the solvent
- Solubility is the maximum amount of solute that can dissolve in a given amount of solvent at a specific temperature
- occurs when a solution contains more dissolved solute than is normally possible under given conditions
Energetics of Dissolution
Energy changes during dissolution
- Dissolution can be exothermic or endothermic
- Exothermic: heat released, solution temperature increases (sodium hydroxide in water)
- Endothermic: heat absorbed, solution temperature decreases (ammonium nitrate in water)
- () is the heat energy change during dissolution
- Negative indicates (heat released)
- Positive indicates (heat absorbed)
- Entropy changes also influence spontaneity of dissolution
- Entropy increases as solute particles disperse in solvent (increased randomness)
- Increased entropy favors spontaneous dissolution (sugar in water)
- change () determines overall spontaneity
- Negative indicates (salt in water)
- Positive indicates nonspontaneous process (oil in water)
Key Terms to Review (43)
$
Delta H$: $
Delta H$ is the change in enthalpy, a thermodynamic property that represents the total energy released or absorbed during a chemical process or physical transformation at constant pressure. It is a measure of the heat energy exchanged between a system and its surroundings, and is a crucial concept in understanding chemical reactions, phase changes, and spontaneity of processes.
$\Delta G$: $\Delta G$, or Gibbs free energy change, is a thermodynamic quantity that measures the maximum reversible work that can be performed by a system at constant temperature and pressure. It helps determine whether a reaction will occur spontaneously; if $\Delta G$ is negative, the reaction can happen without external input, while a positive $\Delta G$ indicates that energy must be added for the process to occur. Understanding $\Delta G$ is crucial for predicting the behavior of chemical processes, especially during dissolution and assessing spontaneity.
$\Delta H_{soln}$: $\Delta H_{soln}$ represents the enthalpy change associated with the dissolution process of a solute in a solvent. This value can be positive or negative, indicating whether the process is endothermic or exothermic. Understanding $\Delta H_{soln}$ helps in determining the energy changes that occur when a solute dissolves, which can influence solubility and concentration effects in solutions.
$\Delta S$: $\Delta S$, or the change in entropy, refers to the measure of disorder or randomness in a system during a process. It indicates how the distribution of energy changes within a system, impacting the spontaneity of processes. When a system undergoes a change, such as dissolving a solute or a reaction, the value of $\Delta S$ can help predict whether that change is likely to occur naturally, highlighting the balance between energy dispersal and organization.
Alloys: An alloy is a homogeneous mixture of two or more elements, where at least one element is a metal. Alloys often have enhanced properties compared to their component elements.
Concentration: Concentration is the measure of the amount of a solute that is dissolved in a given quantity of solvent. It is commonly expressed in terms of molarity (M), which is moles of solute per liter of solution.
Concentration: Concentration is a measure of the amount of a substance present in a given volume or mass of a solution or mixture. It is a fundamental concept in chemistry that is closely related to the study of chemical reactions, equilibrium, and the behavior of solutions.
Dipole-Dipole Interactions: Dipole-dipole interactions are a type of intermolecular force that occurs between polar molecules, where the partially positively charged region of one molecule is attracted to the partially negatively charged region of another molecule. These interactions play a crucial role in the dissolution process, as they can influence the solubility of substances in a given solvent.
Dissolution: Dissolution is the process by which a solute (a substance that is dissolved) disperses and incorporates into a solvent (the dissolving medium) to form a homogeneous solution. This term is central to understanding the fundamental concepts of solubility and precipitation in chemistry.
Endothermic: Endothermic refers to a process or reaction that absorbs heat from the surrounding environment. This means that the system undergoing the endothermic process requires an input of energy in the form of heat in order to proceed. Endothermic processes are central to understanding various topics in chemistry, including energy basics, enthalpy, dissolution, equilibrium, and free energy.
Endothermic process: An endothermic process is a chemical reaction or physical change that absorbs heat energy from its surroundings. These processes result in a decrease in the temperature of the surrounding environment.
Enthalpy of Solution: Enthalpy of solution, also known as heat of solution, is the amount of heat energy released or absorbed when a solute dissolves in a solvent to form a solution. It is a measure of the change in enthalpy that occurs during the dissolution process.
Exothermic: Exothermic refers to a chemical reaction or process that releases energy in the form of heat to the surrounding environment. These reactions produce more energy than they consume, resulting in a net release of heat.
Exothermic process: An exothermic process is a chemical reaction or physical change that releases heat to its surroundings. This release of energy usually results in an increase in the temperature of the surroundings.
Gas in Gas: Gas in gas refers to the dissolution of one gas within another gas. This process is governed by the principles of gas solubility and the interactions between different gas molecules. Understanding gas in gas is crucial in the context of the dissolution process, as it provides insights into the behavior and interactions of gases in various environments.
Gas in Liquid: Gas in liquid refers to the dissolution of a gas within a liquid medium. This process occurs when a gas is able to dissolve and become dispersed throughout a liquid, forming a homogeneous solution. The solubility of the gas in the liquid depends on various factors, such as temperature, pressure, and the chemical properties of both the gas and the liquid.
Gibbs Free Energy: Gibbs free energy is a thermodynamic property that combines the concepts of enthalpy and entropy to determine the spontaneity and feasibility of a chemical process. It is a crucial factor in understanding the driving forces behind chemical reactions and phase changes.
Gibbs free energy (G): Gibbs free energy (G) is a thermodynamic potential that measures the maximum reversible work obtainable from a system at constant temperature and pressure. It is used to predict the direction of chemical reactions.
Homogeneous mixture: A homogeneous mixture is a type of mixture in which the composition is uniform and every part of the solution has the same properties. Examples include saltwater and air.
Homogeneous Mixture: A homogeneous mixture is a type of mixture in which the composition is uniform throughout, with no visible distinction between the different components. It is a single phase system where the properties are the same regardless of the location within the mixture.
Hydration: Hydration refers to the process of adding water or other liquid to a substance, resulting in the formation of a hydrated compound or solution. This term is particularly relevant in the context of dissolution, electrolytes, and hydrocarbon chemistry.
Hydrogen Bonding: Hydrogen bonding is a type of dipole-dipole intermolecular force that occurs when a hydrogen atom covalently bonded to a highly electronegative element, such as nitrogen, oxygen, or fluorine, experiences an attractive force with another nearby highly electronegative element. This attractive force is significantly stronger than a typical dipole-dipole interaction and has a significant impact on the physical and chemical properties of various compounds.
Ideal solution: An ideal solution is a homogeneous mixture in which the enthalpy of mixing is zero, and the components obey Raoult's Law across all concentrations. These solutions exhibit no change in volume or heat when mixed.
Intermolecular forces: Intermolecular forces are the forces of attraction and repulsion between molecules that influence the physical properties of substances. These forces are weaker than intramolecular forces, which hold atoms together within a molecule.
Intermolecular Forces: Intermolecular forces are the attractive or repulsive forces that exist between molecules, as opposed to the intramolecular forces that hold atoms together within a molecule. These forces play a crucial role in determining the physical properties and behavior of substances across various topics in chemistry, including non-ideal gas behavior, the properties of liquids, phase transitions, and the dissolution process.
Like dissolves like: The phrase 'like dissolves like' refers to the principle that substances with similar chemical properties tend to dissolve in one another. This concept highlights the importance of molecular interactions, particularly between polar and nonpolar molecules, which greatly influences the solubility of various substances in a solvent.
London Dispersion Forces: London dispersion forces are a type of intermolecular force that arises from the temporary, spontaneous polarization of atoms or molecules. These forces are the weakest of the intermolecular forces, but they play a crucial role in the properties and behavior of many substances, including liquids, gases, and the noble gases.
Nonpolar solutes: Nonpolar solutes are substances that do not have a significant charge separation, meaning they do not interact favorably with polar solvents like water. This lack of polarity is due to the even distribution of electron density across the molecule, leading to minimal dipole moments. In the context of the dissolution process, nonpolar solutes tend to dissolve well in nonpolar solvents, highlighting the principle that 'like dissolves like' in chemistry.
Polar Solutes: Polar solutes are molecules or ions that possess a partial positive and partial negative charge, creating an unequal distribution of electrons within the molecule. This polarity allows them to interact strongly with polar solvents, such as water, through the formation of hydrogen bonds and other dipole-dipole interactions, facilitating their dissolution.
Polarity: Polarity refers to the unequal distribution of electrons within a molecule, resulting in the creation of partially positive and partially negative regions. This concept is fundamental in understanding the properties and behavior of ionic, molecular, and organic compounds.
Solid in Liquid: A solid in liquid refers to the state of matter where a solid substance is dispersed or dissolved within a liquid medium. This is a common occurrence in various chemical and physical processes, particularly in the context of dissolution and solubility.
Solid in Solid: Solid in solid refers to the presence of a solid phase dispersed within another solid phase, creating a heterogeneous solid-solid mixture. This term is particularly relevant in the context of the dissolution process, where the dissolution of a solid solute into a solid solvent is examined.
Solubility: Solubility is the maximum amount of a substance that can dissolve in a solvent at a given temperature and pressure. It determines how substances interact in solutions.
Solubility: Solubility is a measure of the ability of a substance to dissolve in a solvent, forming a homogeneous solution. It is a fundamental concept in chemistry that describes the maximum amount of a substance that can be dissolved in a given volume of a solvent under specific conditions of temperature and pressure.
Solute: A solute is a substance that is dissolved in a solvent to form a solution. It can be in any phase: solid, liquid, or gas.
Solute: A solute is the substance that is dissolved in a solution, typically in smaller quantities compared to the solvent. It is the component of a solution that is present in a lesser amount and is dispersed throughout the solvent.
Solution: A solution is a homogeneous mixture composed of two or more substances. In a solution, a solute is dissolved in a solvent, resulting in a single phase with a uniform composition and properties throughout.
Solvation: Solvation is the process of surrounding solute particles with solvent molecules to form a solution. It involves interactions between the solute and solvent molecules.
Solvation: Solvation is the process by which solute particles or ions become surrounded by solvent molecules, forming a solvated species. This interaction between the solute and solvent is a critical aspect of the dissolution process, the behavior of electrolytes, and the solubility of substances.
Solvent: A solvent is a substance, typically a liquid, that dissolves a solute to form a solution. The solvent is usually present in greater amount compared to the solute.
Solvent: A solvent is a liquid, solid, or gas that can dissolve other substances, known as solutes, to form a solution. Solvents play a crucial role in various chemical processes, including chemical reactions, extraction, and purification.
Spontaneous process: A spontaneous process is a physical or chemical change that occurs without external intervention. It is driven by a decrease in free energy and an increase in entropy.
Supersaturation: Supersaturation is a state in a solution where the concentration of a dissolved substance exceeds the equilibrium concentration, or the maximum amount that can be dissolved in the solvent at a given temperature and pressure. This metastable condition can lead to the precipitation of the excess solute as the solution returns to equilibrium.