Kinetic Molecular Theory (PDF)

KINETIC MOLECULAR THEORY OF SOLIDS AND LIQUIDS IMFA Kinetic Molecular Theory -​ The kinetic molecular theory of matter provides an overview of the microscopic properties of molecules or atoms and their interactions. -​ It describes the microscopic properties of matter and how they tra...

KINETIC MOLECULAR THEORY OF SOLIDS AND LIQUIDS IMFA Kinetic Molecular Theory -​ The kinetic molecular theory of matter provides an overview of the microscopic properties of molecules or atoms and their interactions. -​ It describes the microscopic properties of matter and how they translate to the state and other properties of matter. Postulates: 1.​ Matter is composed of small particles 2.​ Molecules interact through attractive forces 3.​ Molecules are in constant random motion 4.​ The amount of kinetic energy in a substance is related to its temperature. Intermolecular Force of Attraction (IMFA) -​ Intermolecular forces are attractive forces between molecules. -​ Generally, intermolecular forces are much weaker than intramolecular forces. -​ Dipole-dipole, dipole-induced dipole, and dispersion forces make up what chemists commonly refer to as van der Waals force, after the Dutch physicist Johannes van der Waals 1. Dipole-dipole Forces ​ Attractive forces between polar molecules  ​ The positive side of a polar molecule attracts the negative side of another polar molecule ​ The larger the dipole moment, the greater the force. ​ Examples: HCl and H2S 2. Hydrogen Bonding ​ a special type of dipole-dipole force ​ An attractive force that exists when hydrogen is bonded to the most electronegative atoms, namely F, O, or N ​ Examples: HF, H2O, NH3 & H2O, and (CH3)2CHOH & H2O 3. Ion-dipole Forces ​ attractive forces between an ion and a polar molecule ​ cation interacts with the partially negative side of a polar molecule while the anion interacts with a partially positive side. ​ Use Coulomb's law to determine which ion will have the strongest or weakest interactions with the polar molecule. ​ The magnitude of the force is directly related to the magnitude of charge on the particles and indirectly related to the distance between the particles. ​ The strength of this kind of IMFA increases as the charge of the ion increases, while the distance decreases as the strength of the force increases. ​ Example: NaCl (aq) 4. London Dispersion Forces ​ named after Fritz London ​ present in between all electrically neutral molecules ​ the weakest type of IMFA  ​ attractive forces that arise as a result of temporary dipoles (instantaneous dipoles) induced in atoms or molecules ​ Polarizability refers to the ease at which the electron cloud can be distorted. ​ Examples: He, H2 5. Ion-Induced dipole Force ​ occurs when an ion interacts with a nonpolar molecule ​ the charge on the ion induces polarity in the nonpolar molar molecule ​ Example: Fe2+ & O2 6. Dipole-Induced Dipole Forces ​ weak attraction that results when a polar molecule induces a dipole in an atom or in a nonpolar molecule by disturbing the arrangement of electrons in the nonpolar atom/molecule. ​ Examples: HCl & Ar, H2O & O2 PROPERTIES OF LIQUID 1. Surface Tension -​ Surface tension is the tendency of a fluid to resist an external force and acquire the least possible surface area. -​ Molecules in the interior (below the surface) are attracted equally on all sides, whereas those at the surface are attracted only below and to the sides, producing a net inward force. This inward force makes the molecules at the surface pack closely together, causing the liquid to occupy the smallest possible area and behave like tight skin. -​ Surface tension is higher in liquids that have higher intermolecular forces. Example: Arrange the following molecules in increasing order of surface tension: acetone, ethanol, and glycerol. Answer: acetone < ethanol < glycerol 2. Viscosity -​ It is the measure of fluid’s resistance to flow. -​ Liquids that flow easily have low viscosity, while liquids that do not flow readily have high viscosity. -​ Molecules with stronger IMFA have higher viscosity compared to those with weaker IMFA. -​ The more massive the liquid is, the higher the viscosity. -​ Molecules with long chains have a higher viscosity than shorter molecules because there are more atoms that can attract one another, contributing to the substance’s total attractive forces. This can hinder their flow and make them more resistant to sliding past each other, resulting in higher viscosity. Example: Arrange the following molecules in increasing order of viscosity: acetone, ethanol, and glycerol. Answer: acetone < ethanol < glycerol 3. Solubility -​ It refers to the ability of a substance to dissolve in a given amount of solvent at a specified temperature. -​ When the solute and the solvent both exhibit the same IMFA, they form a solution. -​ Polar molecules are miscible in a polar solvent. -​ Nonpolar molecules are miscible in a nonpolar solvent. -​ Polar molecules and nonpolar molecules do not mix together. -​ The stronger the intermolecular forces between the solvent molecule and the solute molecule, the greater the solubility. Example: water is miscible in alcohol, but immiscible in oil. 4. Vapor Pressure -​ It is the pressure exerted by a vapor in equilibrium with its liquid phase in a closed system. This occurs when the rate of evaporation (liquid molecules escaping into the gas phase) equals the rate of condensation (vapor molecules returning to the liquid phase). -​ Substances with stronger IMFAs have lower vapor pressure compared to those with weaker IMFA. Example: Arrange the following molecules in increasing order of vapor pressure: acetone, ethanol, and glycerol. Answer: glycerol < ethanol < acetone 5. Heat of Vaporization (ΔHvap) -​ It is also called as “enthalpy of vaporization” or “molar heat of vaporization.” -​ It is the amount of energy that must be added to a liquid substance to transform a quantity of that substance into a gas. -​ Vaporization occurs more readily with increased temperature, increased surface area of the liquid, and decreased strength of intermolecular forces. -​ The stronger the intermolecular forces, the higher the heat of vaporization. Example: Arrange the following molecules in increasing order of heat of vaporization: acetone, ethanol, and glycerol. Answer: acetone < ethanol < glycerol 6. Boiling Point -​ It is the temperature at which a substance changes from liquid to gas. -​ Boiling happens when the molecules of a liquid gain enough energy to overcome the intermolecular forces of attraction that hold the molecules together. -​ Liquids with stronger intermolecular forces tend to have higher boiling points, while those with weaker intermolecular forces have lower boiling points. -​ Larger molecules also have more surface area for intermolecular interactions, which means more energy is required to break these interactions during boiling. Example: Arrange the following molecules in increasing order of boiling point: acetone, ethanol, and glycerol. Answer: acetone < ethanol < glycerol PROPERTIES OF SOLIDS Crystalline Solids ​ solids in which the atoms, ions, or molecules are arranged in a definite repeating pattern ​ the orderly arrangement of atoms: highly regular shapes ​ The dots seen in the lattice corners represents a lattice point and consists of a specific atom, molecule, or ion. ​ Crystalline solids are formed from small, repeating units called unit cells.  ​ Unit cells are repeated and arranged, giving rise to a 3-D crystal structure known as a crystal lattice. 1. Covalent Crystals/ Covalent Solids -​ composed of atoms which are covalently bonded to one another Examples: diamond, graphite, charcoal, silicon dioxide/ quartz 2. Metallic Crystals/ Metallic Solids -​ composed of metal atoms bonded together by metallic bonds. have positive metal ions that are attracted by a sea of electrons Examples: platinum, gold, copper, tungsten, silver, iron, brass (copper and zinc) 3. Ionic Crystals/ Ionic Solids -​ composed of alternating positive and negative ions held together by strong coulombic forces Example: Table salt, sodium chloride (NaCl), Calcium fluoride (CaF2), Silver chloride (AgCl), Copper sulfate (CuSO4), Magnesium oxide (MgO) 4. Molecular Crystals/ Molecular Solids -​ held together by weak intermolecular forces Examples: Sucrose (C12H22O11), Iodine (I2), Dry ice (CO2), Silicon tetrachloride (SiCl4) Amorphous Solids ​ from the Greek words for “without form” ​ lacks the order found in crystalline solids ​ structures at the atomic level similar to the structures of liquids ​ atoms, ions, or molecules have little freedom to move unlike in liquids ​ don’t have well-defined shapes of a crystal ​ Examples are glass, plastic, coal, and rubber. CRYSTALLINE VS. AMORPHOUS SOLIDS Intermolecular Forces of Attraction: ​ Crystalline Solids: held together by uniform, strong intermolecular forces of attraction  ​ Amorphous Solids: held together by non-uniform intermolecular forces of attraction Melting/Freezing Point ​ Crystalline Solids: have a precise melting point ​ Amorphous Solids: melt over a wide range of temperature Heat of Fusion (ΔHfus) - quantity of heat necessary to melt a solid ​ Crystalline Solids: fixed and definite ​ Amorphous Solids: no precise value Heat of Sublimation (ΔHsub) - quantity of heat necessary to sublime a solid ​ Crystalline Solids: fixed and definite ​ Amorphous Solids: no precise value Chemical nature ​ Crystalline Solids: anisotropy (the property of substances where the physical and mechanical properties vary with different orientation and molecular axes) ​ Amorphous Solids: isotropy (the property of substances where the physical and mechanical properties are equal in all direction OTHER PROPERTIES OF SOLIDS 1. Malleability - the ability of solid to undergo compressive stress without breaking it 2. Ductility - the ability of solid to undergo tensile stress 3. Electrical Conductivity - the measurement of the ability of atoms, molecules, or ions to transfer electrons from one to another 4. Thermal Conductivity - the measurement of the ability of atoms, molecules, or ions to move and collide with its neighboring particles CREDITS: Ma’am Crisshalyn Pineda PHASE VS STATE PHASE - A phase of matter refers to the physical form of matter (solid, liquid, gas, plasma) based on its temperature and pressure. STATE - A state of matter refers to the chemical composition of matter (element, compound, mixture). Note: The same substance can exist in different phases of matter, but its state of the matter remains constant. PHASE CHANGE - Phase changes occur when matter changes from one physical form to another (e.g. melting, boiling, condensing), while state changes occur when matter undergoes a chemical reaction (e.g. rusting, burning). List of Phase Changes Between States of Matter ​ MELTING - Solid to liquid ​ FREEZING - Liquid to solid ​ VAPORIZATION - Liquid to gas ​ CONDENSATION - Gas to liquid ​ DEPOSITION - Gas to solid ​ SUBLIMATION - Solid to gas PHASE DIAGRAM A phase diagram represents the various physical states or phases of matter at different pressures and temperatures. In other words, it summarizes the effect of pressure and temp1erature on the nature of a substance. 1 Know any good chemistry jokes? Na. Consider the temperature as the X-axis and pressure as the Y-axis. Using coordinates ( ºC, atm ) to plot points then check where it is located. A-B where the solid phase is in equilibrium with its gaseous counterpart. Every point on this line represents the condition under which the solid is in equilibrium with the gas. In other words, the rate at which the solid transforms into gas is the same as when the gas transforms back into solid. B-C contains all the conditions of pressure and temperature at which the liquid boils. Here, the liquid is in equilibrium with the gas. In other words, the boiling rate is equal to the condensation rate. B-D line represents the equilibrium between solid and liquid. Each point on this line depicts the condition under which a solid melts into a liquid. The reverse also holds. The rate of melting is equal to the rate of freezing. The point where the lines intersect is called the triple point. It is the pressure and temperature conditions at which all three phases, solid, liquid, and gas, coexist in equilibrium. The critical point is the highest temperature and pressure at which a gas and a liquid can coexist at equilibrium. Beyond this point, the two phases become indistinguishable and form a phase known as a supercritical fluid.2 2 Hey want to hear a joke about potassium? K. HEATING AND COOLING CURVE an ENDOthermic reaction absorbs energy in the form of heat from its surroundings, whereas an EXOthermic reaction releases energy to the surroundings. At a sloped line, temperature changes as heat is added. Q=mCpΔT or Q=mCp(Tfinal - Tinitial) Where: Q is the heat energy, m is the mass (in grams) of the substance, C is the specific heat capacity, and ΔT is the change in temperature. 3 At the straight horizontal line is when heat is added but the temperature remains constant. Q=m×H Where: Q is the heat energy, m is the mass (in grams) of the substance, and H is the enthalpy of phase changes. E.g. Heat of fusion, Heat of vaporization, etc. To calculate the total heat added, solve for the summation of heat per line. (Q1+Q2+Q3+Q4+…) NOTE: make sure to read the problem carefully to determine the number of q to be combined. 3 Why did the white bear dissolve in water? Because it was polar HEAT REMOVED 4 When the heat is removed, just follow the same process above. Notice that the ΔT is negative because the initial T is higher than the final T. For the H or enthalphy of phase changes, apply the negative sign. Hcrystallization (freezing) = -Hfusion (melting). 4 Gold is the best element because it’s AU-some.  Percentage by Mass, Volume, and Mass/Volume Concentration of Solution The amount of solute present in a solution is described by its concentration. Concentration is an intensive property as it represents the proportion of a substance with respect to the whole solution. Percentage by Mass % m/m also known as mass percent or weight percent (% w/w), is defined as the mass of solute per mass of the solution.The masses of the solute and the solution should be expressed in the same units; hence, the mass fraction is unitless. Sample problem: Calculate the concentration of a solution in percentage by mass prepared by dissolving 12 g of NaCl to produce 50 g of the solution. Percentage by Volume, % v/v also known as volume percent (% v/v), is defined as the volume of solute per volume of the solution. Proof is a commonly used unit for alcohol concentration. It is mathematically defined as two times the percentage by volume of the alcohol in the solution. Sample problem: Calculate the concentration of ethanol, in percentage per volume, in a solution prepared by dissolving 11 mL of ethanol with 10 mL of water. Percentage by Mass per Volume also known as the percentage by weight per volume (% w/v), is defined as the mass of solute per volume of the solution.The mass of the solute is usually expressed in grams, while the volume of the solution is usually expressed in milliliters. 5 5 We'd give you some more chemistry jokes, but all the good ones argon.  6 Sample problem:Calculate the mass of sodium acetate (NaCH3COO), in grams, needed to be dissolved in water to produce a 150 mL solution with a concentration of 20 % m/v. MOLARITY AND MOLALITY OF A SOLUTION Molarity (M) The concentration of aqueous solutions are usually expressed in molarity (M), defined as the number of moles of the solute dissolved in one liter of the solution. ​ Molarity is easy to use especially for aqueous solutions where the solute is solid. ​ Susceptible to temperature changes (Temperature dependent) A.​ Volume —> CF: Molarity —> CF: Mole ratio —> mass ratios = mass in g 6 D’malfi in the bar, Au in a goose.  B.​ Mass —> CF: Mass ratio —> CF: Mole ratio —> Molarity = Volume in L MOLALTY (m) -​ m = mol solute/kg solvent -​ Molal concentration -​ Temperature independent -​ Unit: mol/kg (molal) COLLIGATIVE PROPERTIES -​ Properties of solutions that depend on the concentration of solutes instead of the identity(nature) or mass of solute particles -​ 3 colligative properties exist, including: Vapor Pressure, Boiling Point Elevation, and Freezing Point Depression Vapor Pressure -​ Measure of tendency of a material to change into a gaseous/vapor state. -​ Increases with temperature -​ Raoult’s Law -​ P ₒ ᵤₜᵢₒₙ = (X ₒ ᵥₑₙₜ) (P ₒ ᵥₑₙₜ) -​ X ₒ ᵥₑₙₜ = [n ₒ ᵥₑₙₜ/(n ₒ ᵥₑₙₜ+n ₒ ᵤₜₑ)] Boiling Point Elevation -​ Phenomenon where a solvent’s boiling point increases due to the addition of a solute -​ Higher concentration of solute equates to a higher boiling point -​ △Tb = Tb - Tb° (BP of solution - BP of solvent) -​ (For non electrolyte) △Tb = Kbm ((BPE constant)(molal concentration)) -​ (For electrolyte) △Tb = iKbm(Same as previous but with van't Hoff factor) Freezing Point Depression -​ Phenomenon where a solvent’s freezing point decreases due to addition of solute  -​ Higher concentration equates to a lower freezing poing -​ △Tf = Tf - Tf° (FP of solution - FP of solvent) -​ (For non-electrolyte) △Tb = Kfm -​ (For electrolyte) △Tf = iKfm 7 references: Phase of Matter vs State of Matter: Difference and Comparison List of Phase Changes Between States of Matter Phase Diagram: Definition, Explanation, and Diagram Heating and Cooling Curves — Overview & Examples - Expii GC2-Q3W5-Quipper-Study-Guide-Percentage-by-Mass-Volume-and-Mass-Volume.pdf GC2-Q3W5-Quipper-Study-Guide-Molarity-and-Molality.pdf Sundrin Aian Dorado Eimira Musicque Danan Kevin Jairous Buela 7 I once told a chemistry joke. There was no reaction