Chem 1465 1st Edition Lecture 12Outline of Last Lecture 1. Important terms2. UnitsA. JoulesB. calorieC. Calorie3. First law of thermodynamicsA. First lawB. Algebraic expression4. Sign convention A. DeltaB. System and surrounding5. CalorimetryA. TermsB. Equations6. Pressure-volume workOutline of Current Lecture 1. Enthalpy (H)A. Important relationships B. Thermodynamic propertyThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.C. ΔH and q2. Thermochemical equationsA. EquationB. Three rules for thermochemical equations3. Hess’s law4. Enthalpies of formationCurrent Lecture1. Enthalpy (H)A. Derivation of important relationships- 1- Under constant volume conditions, no pv work can be done. - Many chemical reactions occur in open containers under constant pressure conditionsB. Thermodynamic property- ΔH= ΔH= where H is - If ΔH > 0 then the reaction is endothermic- If ΔH < 0 then the reaction is exothermic C. Two important difference between ΔH and q?- Change in enthalpy is a state function and q is not- ΔH is heat flow under constant pressure conditions and q is heat flow under any conditions2. Thermochemical equations A. Equation: a balanced equation that has ΔHrxn next to it- The stoichiometric coefficients in a thermochemical equation refer to the number of moles of reactants and productsB. Three rules for thermochemical equations- The conditions must specified. Standard condition for all gases is 1atm and 25degrees Celsius unless told otherwise.- When the reaction is reversed, the sign of ΔH changes- The enthalpy change, ΔH, is for the specific number of moles of reactants andproducts.3. Hess’s lawA. Hess’s law states that the total enthalpy of change for any process is the same regardless of whatever process occurs in 1 step or many steps- Keep rewriting the equation to make it look like the target equation and try to cancel out the left and right side (of things not in the target equation)4. Enthalpies of formationA. A formation reaction: forming 1 mole of a substance from its elemental form (using the most stable elemental forms).B. Standard enthalpy of formation: the change in enthalpy that occurs when one mole of substance is formed. Sometimes fractional coefficients are required.- As a consequence of Hess’s law, we can use ΔH degrees F to calculate the ΔHrxn. - Just remember: products minus
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