Lecture 2 Notes—Ch.13, Pt.2— Energy Changes When Creating Solution - Enthalpy (Heat) decrease ↓ - Entropy (Disorder & Randomness) increase ↑ Concentration Units - Molarity (M): Moles of solute per liter of solution. M =(moles of solute)(liters of solution) o PROBLEM — Temperature dependent. - Molality (m): Amount of moles of solute dissolved in a kilogram of entire solution. m =(moles of solute)(mass of solute)+(mass of solvent)=(moles of solute)(total mass) o Independent of temperature. - Molarity & Molality have same value when solution is very dilute. - Mole Fraction (Χi): Ratio of moles of one component to total number of moles in mixture. Χi=n1n1+ n2+ n3+ ⋯ (i = 1,2, 3, …)=n1ntot o Could be used to find partial pressure. Χi=P1Ptot o Independent of temperature. - Mole Percentage =(Mole Fraction)× 100 - Mass Fraction: Ratio of mass of one component to total mass of mixture. Mass Fraction =(mass)1(mass)tot - Percent by Mass =(Mass Fraction)× 100 - Percent by Mass = Parts per Hundred o Parts per Million (ppm) and Parts per Billion (ppb) are also common. ppm =(Mass Fraction)× 106 ppb = (Mass Fraction) × 109  Example) Mercury poisoning & Cadmium poisoningChoices of Units - Molarity— Commonly used since volume of solution is easy to measure. - Molality— Independent of temperature. - Mole Fraction— Used for gas and vapor pressure of solution. - Percent by Mass— Independent of Temperature. Need not know molar masses. Conversion Between Units - Requires use of density if any mass to volume or volume to mass conversion needed. - Strategy 1) Write down what you’re starting with. 36.0g HCl100.0g HCl soln 2) Write down what your target is. 36.0g HCl100.0g HCl soln → mol HClliters HCl soln 3) Convert. 36.0g HCl100.0g HCl soln.×1mol HCl36.46g HCl×1.19g HCl soln.1mL HCl soln.×103mL HCl soln.1L HCl soln.= 11.7mol HClL HCl soln.= 11.7M HCl Factors Affecting Solubility 0) Structure— very important and basic 1) Temperature - Example) Solubility of gas decreases as temperature