Name: hydrophobic effects in solvation
Uploaded: 2023-04-30T18:28:32.000Z
Duration: 2 min 5 s
Channel: JoVE

K12 Standards

Tennessee Academic Standards

High School

Chemistry

motion-and-stability-forces-and-interactions

Motion and Stability: Forces and Interactions

CHEM1.PS2.3

Entropy and Solvation

אנטרופיה, S, משקפת את ההסתברות להשיג מצב נתון במערכת. במערכת מבודדת, תהליך מתרחש באופן ספונטני כאשר הוא גורם לעלייה באנטרופיה הכוללת.
השינוי באנטרופיה הנובע מהיווצרות תמיסה הנקראת אנטרופיה של ערבוב, או ערבוב Δ S, אינו תלוי באינטראקציות בין-מולקולריות כלשהן.
במהלך היווצרות התמיסה, המומס והממס עוברים ערבוב, והמומס מתפזר לתוך הממס. מולקולות הממס המקיימות אינטראקציה ישירה עם המולקולות המומסות נקראות ביחד מעטפת הממס או כלוב הממס.
בשל היווצרות קליפות הממס, לממס יש פחות תצורות שקולות אנרגטית מאשר למומס, והמומס צובר אנטרופיה על חשבון האנרגיה מהממס.
כאשר פחמימן מומס במים, מולקולות המים בממשק מים-פחמימנים מתארגנות מחדש כדי למקסם את מספר קשרי המימן שהן יוצרות זו עם זו. חלק מהמים הממסים הופכים למים של קליפות הממס וכתוצאה מכך נוצר כלוב ממס סביב כל מולקולת פחמימנים.
למים במעטפת הממס יש סידור מסודר יותר וחופש תנועה מופחת בהשוואה למים הממסים. זה מוריד את האנטרופיה של המים במעטפת הממס בהשוואה לזו של המים הממסים. לפיכך, הפירוק מלווה בירידה באנטרופיה.
לחלופין, אם מולקולות הפחמימנים מתקבצות יחד, מי המסת האנטרופיה הנמוכה משתחררים והופכים למים ממסים בעלי אנטרופיה גבוהה יותר, ובכך מגדילים את האנטרופיה.
הפרדה מונעת אנטרופיה זו של מולקולות פחמימנים ומים מכונה אפקט הידרופובי. גושים של פחמימנים הוא המועדף בגלל הגידול הקשורים אנטרופיה, וכתוצאה מכך פחמימנים נפרדים שכבות מים.

אנטרופיה ומסיסה

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 תהליך הקפת המומס בממס נקרא המססה. זה כרוך בפיזור שווה של המומס בתוך הממס. כלל האצבע לקביעת ממס לתרכובת נתונה הוא "דומה נמס בדומה לו". לממס טוב יש מאפיינים מולקולריים דומים לאלו של התרכובת שיש להמיס. לדוגמה, תמיסות קוטביות ממיסות מומסים קוטביים, וממיסים לא קוטביים ממיסים מומסים א-קוטביים. ממס קוטבי הוא ממס בעל קבוע דיאלקטרי גבוה (ϵ ≥ 15); ממס אפולארי הוא כזה עם קבוע דיאלקטרי נמוך. הקבוע הדיאלקטרי מוגדר על ידי החוק האלקטרוסטטי, המעניק את אנרגיית האינטראקציה E בין שני יונים עם מטענים
 
 q
 
 
 1
 
 ו
 
 q
 
 
 2
 
 בהתאמה המופרדים במרחק r. ממס קוטבי מפריד או מגן ביעילות יונים זה מזה. לכן, הנטייה של יונים בעלי מטען הפוך לקשר היא פחותה בממס קוטבי מאשר בממס לא קוטבי.
 
 
 במקרה של פחמימן ומים, האחד הוא קוטבי (מים), והשני הוא לא קוטבי (פחמימן). בהחדרת מולקולות פחמימנים למים, מולקולות המים לאורך ממשק הפחמימן-מים יוצרות סידור דמוי מעטפת הנקרא מעטפת הממס סביב כל מולקולת פחמימנים. המים בתוך הסדרים דמויי קליפה אלה מסודרים יותר ויש להם אנטרופיה נמוכה יותר בהשוואה למים בממס. מכיוון שכל מערכת בטבע מנסה להשיג מצב של אנטרופיה מקסימלית, המערכת מנסה למזער את האינטראקציות בין פחמימנים למים, וכתוצאה מכך נוצרות שכבות פחמימנים ומים נפרדות. הפרדה מונעת אנטרופיה זו בין פחמימנים ומים מכונה האפקט ההידרופובי.
 
 
 מכיוון שאנטרופיה היא הגורם המניע את אי מסיסות הפחמימנים במים, טמפרטורת המערכת משפיעה גם על התהליך, למשל בהידרטים או קלתרטים של גז, אחד מהמאגרים הגדולים ביותר של גז טבעי. הידרטים של גז הם צורות מוצקות גבישיות של מים וגז. הם נוצרים כאשר מתאן ומים קופאים תחת לחצים גבוהים וטמפרטורות נמוכות. מולקולות הפחמימנים סגורות בתוך כלובי קרח יציבים, שיש לו חללים פתוחים גדולים יחסית במבנה הגבישי שלו. מולקולות הפחמימנים משתלבות בתוך החורים הללו, מה שמאפשר לחזות את הגודל המרבי של מולקולות הפחמימנים שיכולות ליצור קלתרטים.
 
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התהליך של הקפת מומס בממס נקרא המסה. זה כרוך בהפצה שווה של המומס בתוך הממס. כלל אצבע ל...

Education

JoVE Core

Organic Chemistry

כימיה אורגנית

Unit 1

יחידה 1

Thermodynamics and Chemical Kinetics

תרמודינמיקה וקינטיקה כימית

KEY TERMS AND CONCEPTS

מונחים ומושגים מרכזיים

hydrophobic effects in solvation

Solvation is the process of surrounding a solute with solvent. It spreads the solute evenly through the solvent. A useful rule is that like dissolves like. A good solvent has molecular features similar to the substance being dissolved.

Polar solvents dissolve polar solutes, and apolar solvents dissolve apolar solutes. A polar solvent has a high dielectric constant, with ε greater than or equal to 15. An apolar solvent has a low dielectric constant. The dielectric constant is defined by the electrostatic law, which describes the interaction energy between two ions with charges q1 and q2 separated by a distance r.

A polar solvent can separate or shield ions from one another. Because of this, oppositely charged ions are less likely to associate in a polar solvent than in an apolar solvent. Water and hydrocarbons show this difference clearly. Water is polar, while hydrocarbons are apolar.

When hydrocarbon molecules are added to water, the water at the interface forms a shell-like arrangement around each molecule. This shell is called the solvent shell. The water inside these shells is more ordered and has lower entropy than the surrounding water. Since natural systems tend to move toward maximum entropy, the system reduces contact between hydrocarbon and water and forms separate layers.

This entropy-driven separation is called the hydrophobic effect. Because entropy drives the insolubility of hydrocarbons in water, temperature also affects the process. This is seen in gas hydrates, also called clathrates, which are among the largest reserves of natural gas.

Gas hydrates are crystalline solids made of water and gas. They form when methane and water freeze under high pressure and low temperature. The hydrocarbon molecules are trapped in stable cages of ice. Ice has relatively large open spaces in its crystal structure, so hydrocarbon molecules can fit inside these holes. That makes it possible to predict the maximum size of hydrocarbon molecules that can form clathrates.

Hydrophobic Effects in Solvation

chemical reactions

Stoichiometry, Rates, and Equilibrium

Stoichiometry, reaction rates, and equilibrium explain how chemical reactions are measured and predicted. A balanced chemical equation shows the chemical formulas of the reactants and products in a chemical change. It also gives the relative amounts of each substance involved. Reaction stoichiometry helps predict how much reactant is needed to make a desired amount of product. It can also show how much product forms from a given amount of reactant. The amounts shown by a balanced equation are...

enthalpy and heat of reaction

Combustion Heat and Hydrocarbon Stability

Combustion is a burning reaction that releases energy as heat, light, or sound. It happens when a substance reacts with an oxidizing agent, usually molecular oxygen. The heat of combustion is also called the enthalpy of combustion. The energy released when one mole of a substance undergoes complete combustion at constant pressure is the molar heat of combustion. Combustion reactions are exothermic, so they give off energy. For that reason, the sign of ΔH is negative. In 1772, Antoine Lavoisier...

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Why Some Solutions Form Spontaneously

Solution formation can happen spontaneously under the right conditions. A spontaneous process is one that occurs without energy from an outside source. During dissolution, solute and solvent particles separate and then attract each other in a new way. The energy change depends on the balance of intermolecular forces, which are the attractions between particles. If the solute-solute and solvent-solvent forces are about the same as the new solute-solvent forces, the solution forms with no energy...

entropy and solvation

Solvation is the process of surrounding a solute with solvent. It spreads the solute evenly through the solvent. A useful rule is that like dissolves like. A good solvent has molecular features similar to the substance being dissolved. Polar solvents dissolve polar solutes, and apolar solvents dissolve apolar solutes. A polar solvent has a high dielectric constant, with ε greater than or equal to 15. An apolar solvent has a low dielectric constant. The dielectric constant is defined by the...

gibbs free energy and thermodynamic favorability

gibbs-free-energy-and-thermodynamic-favorability

Temperature Effects on Gibbs Free Energy

Temperature changes can decide whether a process is spontaneous. This idea applies to phase changes and to some chemical reactions. The key link is Gibbs free energy, which connects free energy change with enthalpy and entropy. The sign of the Gibbs free energy change, or ΔG, depends on the signs of enthalpy change (ΔH) and entropy change (ΔS), and sometimes on the absolute temperature. Because temperature is measured in kelvin, it is always a positive value. That means there are four main...

chemical and solubility equilibria

How Solubility Depends on Free Energy

Solubility depends on free energy changes when a solute dissolves in a solvent. The free energy change for this process is called the free energy of solution, ΔGsolution. When ΔGsolution is less than zero, solution formation is favorable. When it is greater than zero, solution formation is unfavorable. For complete dissolution to happen, the Gibbs energy change must be negative. This means the balance of forces in the mixture must favor solution formation. The amount a solute dissolves in a...

rate law and reaction order

How Reactant Concentration Sets Reaction Rate

Reaction rate depends on reactant concentration, and rate laws show that relationship with a mathematical equation. A rate law, also called a differential rate law or rate equation, links the rate of a chemical reaction to the concentrations of its reactants. For a generic reaction, a A + b B  products, the rate law can be written as rate = k [A]^m [B]^n. Here, [A] and [B] are the molar concentrations of the reactants. The constant k is the rate constant, and it is specific to one reaction at...

effect of temperature change on reaction rate

effect-of-temperature-change-on-reaction-rate

Arrhenius Equation in Reaction Speed

The Arrhenius equation connects activation energy, temperature, and the rate constant, k, for many chemical reactions. It helps explain why some reactions move slowly while others happen faster. In this equation, R is the ideal gas constant, with a value of 8.314 J/mol·K. T is the temperature in kelvin, Ea is the activation energy in joules per mole, e is the constant 2.7183, and A is the frequency factor. The frequency factor, A, describes how often reacting molecules collide and how well...

multi-step reactions

Reaction Mechanisms and Rate-Determining Steps

Chemical reactions can happen in a sequence of steps. A balanced chemical equation shows the reactants and products, but it does not show how the reaction occurs at the molecular level. The reaction mechanism, or reaction path, gives that step-by-step detail. Each step in a mechanism is an elementary reaction. These elementary reactions happen in order, and together they add up to the balanced equation for the overall reaction. In a multistep mechanism, one step is often much slower than the...

bond dissociation energy and activation energy

bond-dissociation-energy-and-activation-energy

How Bond Strength Shapes Reaction Speed

Bond strength and activation energy help explain why organic reactions happen. Bond energy is the energy needed to break a bond homolytically, which means each atom takes one of the shared electrons. When a bond value is given for one specific bond, it is called bond dissociation energy. When it is given for a bond type across many compounds, it is called average bond energy. Bond dissociation energy usually follows a clear pattern. A single bond is weaker than a double bond, and a double bond...

energy diagrams, transition states, and intermediates

energy-diagrams-transition-states-and-intermediates

Reaction Coordinate Diagrams in Chemical Reactions

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predicting reaction outcomes

How Temperature Changes Reaction Rate

Reaction rate and reaction pathway are key ideas in chemical kinetics. Thermodynamics, by contrast, focuses on the state of a system. It describes the properties, behavior, and components of reactants and products. It does not describe the path of the process or the speed of the reaction. Kinetics gives information on the atomic or molecular level, while thermodynamics focuses on the energetics of the reactants and products. Thermodynamics can show what may happen in a reaction, but it does...

key terms and concepts

Learn how solvation depends on polarity, dielectric constant, and entropy, and why hydrocarbons separate from water through the hydrophobic effect.

Hydrophobic Effects in Solvation | JoVE K12

organic chemistry

JoVE Core Organic Chemistry explains basic concepts of stereochemistry, reactions, and mechanisms using concise and easy-to-understand animated video lessons. Additionally, the scientist-in-action videos demonstrate the application of related concepts in classical and original research experiments performed in today's laboratories worldwide.

Types of Chemical Bonds

Chemical bonding theories were pioneered by American chemist Gilbert&#xA0;N. Lewis. He developed a model called the Lewis model to explain the type and ...

Chemical Bonds


Atoms participate in a chemical bond formation&#160;to acquire a completed valence-shell electron configuration similar to that of the noble gas nearest ...

Ionic Bonding and Electron Transfer

Ions are atoms or molecules bearing an electrical charge. A cation (a positive ion) forms when a neutral atom loses one or more electrons from its valence ...

Covalent Bonding and Lewis Structures

Compared to ionic bonds, which results from the transfer of electrons between metallic and nonmetallic atoms, covalent bonds result from the mutual ...

Lewis Symbols and the Octet Rule

Chemical bonds are complex interactions between two or more atoms or ions, which reduce the potential energy of the molecule. Gilbert N. Lewis developed a ...

Draw, identify, and contrast graphical representations of chemical bonds (ionic, covalent, and metallic) based on chemical formulas. Construct and communicate explanations to show that atoms combine by transferring or sharing electrons. EXPLANATION: This standard resumes discussions of interactions between atoms from 7.PS1. In seventh grade, students observed patterns within the periodic table that related the physical and chemical properties of substances to the location of the constituent elements on the periodic table. Revisiting general trends is likely to be necessary however a focus should be placed on the transfer of electrons underlying differences in the differences in properties. It is beneficial to show that electrostatic interactions occur even between two non-conductors. Demonstrations can be carried out by using static charge to hold a balloon against a wall or showing that oppositely charged pieces of invisible tape are attracted not only to each other but also to a neutral conductors and non-conductors such as foil strips or paper.

CHEM1.PS2.1

intermolecular-forces-and-physical-properties

Intermolecular Forces and Physical Properties



Intermolecular forces are attractive forces that exist between molecules. They dictate several bulk properties, such as melting points, boiling points, ...

comparing-intermolecular-forces-melting-point-boiling-point

Comparing Intermolecular Forces: Melting Point, Boiling Point, and Miscibility

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Intermolecular vs Intramolecular Forces

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Intermolecular Forces in Solutions

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Exceptions to the Octet Rule

Many covalent molecules have central atoms that do not have eight electrons in their Lewis structures. These molecules fall into three categories:


	...

Understand that intermolecular forces created by unequal distribution of charges result in the varying degrees of attraction between molecules. Compare and contrast the intermolecular forces (hydrogen bonding, dipole-dipole bonding and London dispersion forces) within different types of simple substances (only those following the octet rule) and predict and explain their effect on chemical and physical properties of those substances using models or graphical representations. EXPLANATION: This standard resumes where students left off in 7.PS1. Students' first exposure to all three phases of matter was in third grade, by fifth grade students were investigating phase changes in matter. These discussions have not included a mechanism to explain why states of matter are dependent on temperature and pressure. Students should consider this standard in conjunction with CHEM1.PS2.1 to explore differences in intermolecular attractions within molecular and ionic compounds and the behavior of electrons leading to these differences.

CHEM1.PS2.2

Solution Formation

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Energetics of Solution Formation

The formation of a solution is an example of a spontaneous process, which is a process that occurs under specified conditions without energy from some ...

Chemical and Solubility Equilibria

The free energy change associated with dissolving a solute in a liter of solvent is called the free energy of a solution, &#916;Gsolution. The overall ...

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Solubility Equilibria: Overview

Consider a saturated solution of sparingly soluble salt calcium fluoride with excess solid calcium fluoride. The already dissolved calcium fluoride has ...

Physical Properties Affecting Solubility

Solutions of Gases in Liquids
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solubility-equilibria-ionic-product-of-water

Solubility Equilibria: Ionic Product of Water

Water is a weak electrolyte and undergoes a small amount of self-ionization.
At any given temperature, the concentration of undissociated water is ...

Construct a model to explain the process by which solutes dissolve in solutes, and develop an argument to describe how intermolecular forces affect the solubility of different chemical compounds. EXPLANATION: A similar task and standard exist in the fifth grade (5.PS1.3). At that time, students performed an investigation (which is again mentioned in CHEM1.PS2.4) into factors affecting solubility. However, student background knowledge was not sufficient to explore any explanation of their results. Explorations into intermolecular attractions in the previous standard (CHEM1.PS2.2) have introduced students to the existence of forces between molecules in a substance. Students can now apply these attractions to form explanations for how solute-solute, solute-solvent, and solvent-solvent attractions all interact as substances dissolve. (Solubility constants and saturation of solutions are beyond the scope of this standard.)

Temperature Dependence on Reaction Rate

The Collision Theory
Atoms, molecules, or ions must collide before they can react with each other. Atoms must be close together to form chemical bonds. ...

Predicting Reaction Outcomes

Kinetics describes the rate and path by which a reaction occurs. In contrast, thermodynamics deals with state functions and describes the properties, ...

Conduct an investigation to determine how temperature, surface, and stirring affect the rate of solubility. Construct an argument to explain the relationship observed in experimental data using collision theory. EXPLANATION: This standard is nearly identical to a fifth grade standard which explores factors affecting the solubility of a compound. Though collision theory is more closely related to rates of reaction, in this case the application of collision theory explores how the same factors underlying collision theory for how reactions also facilitate solvation processes.

CHEM1.PS2.4

Hydrophobic Effects in Solvation

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