Melting and Boiling Point

7 Key excerpts on "Melting and Boiling Point"

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  Foundations of College Chemistry

  • Morris Hein, Susan Arena, Cary Willard(Authors)
  • 2021(Publication Date)
  • Wiley

    (Publisher)

  • A meniscus is evidence of cohesive and adhesive forces: • It is concave if the adhesive forces are stronger than the cohesive forces. • It is convex if the cohesive forces are stronger than the adhesive forces. • During evaporation, molecules of greater-than-average kinetic energy escape from the liquid. • Sublimation is the evaporation of a solid directly to a gas. • Gaseous molecules return to the liquid state through condensation. • At equilibrium the rate of evaporation equals the rate of condensation. • The pressure exerted by the vapor in equilibrium with its liquid in a closed container is the vapor pressure of the liquid. • A volatile substance evaporates readily. 13.3 Boiling Point and Melting Point KEY TERMS: boiling point normal boiling point vapor pressure curve melting point (or freezing point) • The boiling point of a liquid is the temperature at which its vapor pressure equals the atmospheric pressure: • At 1 atm the boiling point is called the normal boiling point for a liquid. • The temperature at which a solid is in equilibrium with its liquid phase is the freezing point or melting point. 13.4 Changes of State KEY TERMS: heat of fusion heat of vaporization • A graph of the warming of a liquid is called a heating curve: • Horizontal lines on the heating curve represent changes of state: • The energy required to change 1 g of solid to liquid at its melting point is the heat of fusion. • The energy required to change 1 g of liquid to gas at its normal boiling point is the heat of vaporization. • The energy required to change the phase of a sample (at its melting or boiling point) is energy = (mass)(heat of fusion (or vaporization)) • The energy required to heat molecules without a phase change is determined by energy = (mass)(specific heat)(Δt) 13.5 Intermolecular forces KEY TERMS: intermolecular forces intramolecular forces dipole–dipole attractions hydrogen bond London dispersion forces • Dipole–dipole attractions exist among polar molecules.

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  eBook - PDF

  Foundations of College Chemistry

  • Morris Hein, Susan Arena, Cary Willard(Authors)
  • 2016(Publication Date)
  • Wiley

    (Publisher)

  294 CHAPTER 13 • Liquids As heat is removed from a liquid, the liquid becomes colder and colder, until a tempera- ture is reached at which it begins to solidify. A liquid changing into a solid is said to be freez- ing, or solidifying. When a solid is heated continuously, a temperature is reached at which the solid begins to liquefy. A solid that is changing into a liquid is said to be melting. The tempera- ture at which the solid phase of a substance is in equilibrium with its liquid phase is known as the melting point or freezing point of that substance. The equilibrium equation is solid melting ⥫    ⥬ freezing liquid When a solid is slowly and carefully heated so that a solid–liquid equilibrium is achieved and then maintained, the temperature will remain constant as long as both phases are present. The energy is used solely to change the solid to the liquid. The melting point is another physical property that is commonly used for characterizing substances. The most common example of a solid–liquid equilibrium is ice and water. In a well-stirred system of ice and water, the temperature remains at 0°C as long as both phases are present. The melting point changes only slightly with pressure unless the pressure change is very large. 13.4 Changes of State Calculate the amount of energy involved in a change of state. The majority of solids undergo two changes of state upon heating. A solid changes to a liquid at its melting point, and a liquid changes to a gas at its boiling point. This warming process can be represented by a graph called a heating curve (FIGURE 13.8). This figure T he chemical reaction between Mentos and diet soda has been seen everywhere from chemistry classrooms to YouTube. The Mentos candy fizzes, the diet soda sprays out in a tall fountain, and everyone laughs.

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  Chemistry for Today

  General, Organic, and Biochemistry

  • Spencer Seager, Michael Slabaugh, Maren Hansen, , Spencer Seager, Spencer Seager, Michael Slabaugh, Maren Hansen(Authors)
  • 2021(Publication Date)
  • Cengage Learning EMEA

    (Publisher)

  ● Bubbles of vapor form within the liquid and rise to the surface as the liquid boils. ● The boiling point of a liquid changes as the prevailing atmo- spheric pressure changes. 6.14 Sublimation and Melting Learning Objective: Can you demonstrate an understanding of the processes of sublimation and melting? ● Solids, like liquids, have vapor pressures that increase with temperature. ● Some solids have vapor pressures high enough to allow them to change to vapor without first becoming a liquid, a process called sublimation. ● Most solids change to the liquid state before they change to the vapor state. ● The temperature at which solids change to liquids is called the melting point. Copyright 2022 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 192 Chapter 6 6.15 Energy and the States of Matter Learning Objective: Can you do calculations based on energy changes that accompany heating, cooling, or changing the state of a substance? ● Energy is absorbed or released when matter is changed in temperature or changed from one state to another. ● The amount of heat energy required to produce temperature changes is called the specific heat of the matter involved. ● For phase changes, the amount of heat required is called the heat of fusion, or of vaporization. 1. Calculation of volume from mass and density (Section 6.1): V 5 m d Equation 6.1 2. Calculation of kinetic energy of particles in motion (Section 6.2): K.E. 5 1 2 mv 2 Equation 6.2 3. Boyle’s law (Section 6.7): P 5 k V PV 5 k Equation 6.3 Equation 6.4 4. Charles’s law (Section 6.7): V T 5 k9 V 5 k9T Equation 6.5 Equation 6.6 5.

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  Macroscale and Microscale Organic Experiments

  • Kenneth Williamson, Katherine Masters(Authors)
  • 2016(Publication Date)
  • Cengage Learning EMEA

    (Publisher)

  You can often predict the boiling point, melting point, or solubil-ity of one structure relative to other structures. In fact, as your knowledge grows, you may be able to predict a compound’s approximate melting or boiling tempera-ture based on its structure. Your understanding of intermolecular attractive forces will be very useful in this chapter’s experiments on Melting and Boiling Points, and those in Chapters 5 and 6 that involve distillation and boiling points. Melting Points and Boiling Points PRE-LAB EXERCISE: Draw the organic compounds, identify the inter-molecular attractive forces for each, and list them in order of increasing boiling point as predicted by the relative strength of those intermolecular forces: (a) butane, (b) i -butanol, (c) potassium acetate, and (d) acetone. CHAPTER 3 Copyright 2017 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 42 Macroscale and Microscale Organic Experiments We know that methane is called natural gas because methane’s physical state at room temperature (20°C = 68°F) is a gas. Its London forces are so weak that methane must be cooled to −162°C at 1 atm of pressure before the mol-ecules will stick together enough to form a liquid. Hexane is a very common 1 . L O N D O N A T T R A C T I V E F O R C E S ( O F T E N C A L L E D V A N D E R W A A L S F O R C E S ) Organic molecules that contain only carbon and hydrogen (hydrocarbons) are weakly attracted to each other by London forces. Though weak, these attrac-tive forces increase as molecular size increases.

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  Basic Concepts of Chemistry

  • Leo J. Malone, Theodore O. Dolter(Authors)
  • 2012(Publication Date)
  • Wiley

    (Publisher)

  368 CHAPTER 11 The Solid and Liquid States 11-3 The Solid State: Melting Point LOOKING AHEAD! Heat is a measure of kinetic energy, the energy of motion. There- fore, heating a solid substance increases the motion of the molecules or ions. Eventually, the particles’ motion will overcome the forces holding the molecules or ions in place and the lattice begins to come apart or melts. We will discuss different types of solids in this section and how intermolecular forces affect the temperature at which they melt. n On a hot summer afternoon, ice cream melts too fast and water evaporates quickly. In fact, we may all feel as if we are “melting.” The process of melting is understand- able from kinetic theory. As the temperature increases, the average kinetic energy of molecules increases, which means that they move faster and faster. The increased motion of the molecules eventually overcomes whatever forces are holding the solid or liquid molecules together, and a phase change occurs. It’s like a feeling that most of us have experienced. Sometimes we just get too “fidgety” to stay seated and we have to move around. Why do some solids melt at a certain temperature while others require a higher temperature to melt? The situation is analogous to what happens in an earthquake that begins slowly and intensifies. At first, only the flimsiest buildings collapse. As the earthquake intensifies, stronger and sturdier buildings are affected and collapse. The buildings with the strongest structure may collapse only in the strongest quake. Heating solids is much like subjecting them to an earthquake. A rising temperature causes the molecules or ions of a solid to vibrate more and more vigorously. Solids whose basic particles are not strongly attracted to each other are the first to come apart, so they melt or vaporize at the lower temperatures. At higher temperatures, solids whose particles have stronger attractive forces change to the liquid state.

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  Handbook of Property Estimation Methods for Chemicals

  Environmental Health Sciences

  • Donald Mackay, Robert S. Boethling, Donald Mackay, Robert S. Boethling(Authors)
  • 2000(Publication Date)
  • CRC Press

    (Publisher)

  29 1-56670-456-1/00/$0.00+$.50 © 2000 by CRC Press LLC 2 Boiling Point Warren J. Lyman CONTENTS 2.1 Introduction ........................................................................................................................... 29 2.2 Overview of Available Estimation Equations .................................................................. 30 2.3 Overview of Recommended Methods .............................................................................. 34 2.4 Description of Recommended Methods ........................................................................... 34 2.4.1 Banks’ Molecular Weight Correlation ................................................................... 34 2.4.2 Burnop’s Rule – A Modified Molecular Weight Correlation .............................. 35 2.4.3 Melting Point Correlation ....................................................................................... 36 2.4.4 Simamora and Yalkowsky’s Method for Aromatic Compounds ...................... 38 2.4.5 Cramer’s BC(DEF) Method ..................................................................................... 38 2.4.6 Stein and Brown’s Group Contribution Method ................................................. 43 2.4.7 Lai et al. Nonlinear Group Contribution Method ............................................... 45 References ..................................................................................................................... 49 2.1 Introduction The boiling point is defined as “the temperature at which a liquid’s vapor pressure equals the pressure of the atmosphere on the liquid.” If the pressure is exactly 1 atmosphere (101,325 Pa), the temperature is referred to as “the normal boiling point.” Pure chemicals have a unique boiling point, and this fact can be used in some laboratory investigations to check on the identity and/or purity of a material. Mixtures of two or more compounds have a boiling point range.

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  Chemistry

  The Molecular Nature of Matter

  • Neil D. Jespersen, Alison Hyslop(Authors)
  • 2021(Publication Date)
  • Wiley

    (Publisher)

  During melting, the particles held rigidly in the solid begin to separate slightly as they form the mobile liquid phase. The poten- tial energy increase accompanying this process equals the amount of heat input during the melting process. During boiling, there is an even greater increase in the distance between the molecules. Here they go from the relatively tight packing in the liquid to the widely spaced distribution of molecules in the gas. This gives rise to an even larger increase in the potential energy, which we see as a longer flat region on the heating curve during the boiling of the liquid. The opposite of a heating curve is a cooling curve (see Figure 11.27b). Here we start with a gas and gradually cool it—that is, remove heat from it at a constant rate—until we have reached a solid. Superheating and Supercooling Looking at Figure 11.27 again we notice two unusual features, one on each curve. There is a small “blip” on the heating curve near the transition from the liquid to a gas. A similar feature occurs when a liquid is cooled to a solid. These “blips” represent the phenomena of superheating and supercooling. Superheating occurs when the liquid is heated above the boiling point without boiling. If disturbed, a super- heated liquid will erupt with a shower of vapor and liquid. Many people have discovered this effect when heating their favorite beverage in a microwave oven. When cooling a liquid it is possible to decrease the temperature below the freezing point without solidification occurring, resulting in a supercooled liquid. Once again, if the supercooled liquid is disturbed, very rapid crystallization occurs. Molar Heats of Fusion, Vaporization, and Sublimation Because phase changes occur at constant temperature and pressure, the potential energy changes associated with melting and vaporization can be expressed as enthalpy changes.

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