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Larger surface area and more contact area between molecules increase strength of force Properties of Water: oLiquid water expands upon freezing The water molecules slow down and form a more spread out, solid lattice In the lattice, each water molecule is farther apart than in a liquid This is why: Ice cubes float because they are less dense than liquid water Water bottles and soda cans explode in the freezer Snowflakes have hexagonal shapes Phases of Matter: oSolid: Particles are very close Fixed volume Definite shape oLiquid: Particles farther apart Fixed volume Indefinite shape oGas: Particles are independent and far apart Expand to completely fill the container Easily compressible oOne of the contributing factors to phase change is temperature Higher temperature = molecules have faster speed and more KE Lower temperature = molecules have slower speed and less KE oThe phase of matter (solid, liquid, gas) depends on the strength of the intermolecular forces and how much the heat (temperature and KE) can overcome it Pressure plays a role too
CHEM 113 EXAM 4Critical Temperature (Tc)oThe highest temperature which a distinct liquid phase can exist oWeaker IM forces = lower critical temperature Critical Pressure (Pc) oPressure required to liquefy a gas at the critical temperature Phase Diagram: oTemperature vs. pressure plot that summarizes the conditions under which the different phases of matter occuroRegions: Critical Point (point B): Critical temperature and critical pressure Beyond this point is a supercritical fluid oHas properties of liquid and gases simultaneously Triple Point (point A): Solid, liquid, and gas all present in equilibriumSolution: oHomogenous mixture of two or more substances oSolvent: Substance present in greatest amountIf the solvent is water, we call this solution aqueous oSolute: Substance present in lesser amount Steps in a solution formation: oEX: KCl (a soluble ionic compound) dissolving in wateroStep 1: Solute separation KCL is broken apart into K and Cl ions oStep 2: Solvent separation Solvent (water) molecules separate from each other oStep 3: Solvation K and Cl ions are attracted to the delta minus and delta plus charges on the water molecules by ion-dipole forces If the solvent is water, we call this step hydration oSteps 1-3 occur simultaneously Energetics of steps 1-3: oStep 1: Breaking ionic bonds Requires energy Delta H > 0oStep 2: Breaking IM forces (H-bonds)
CHEM 113 EXAM 4Requires energyDelta H >0 oStep 3: Forming ion-dipole forces Releases energy Delta H <0 o