Lecture 4 Announcements PDF

Lecture #4, p. 1 Lecture 4: Announcements Today: Brown 5.1 The Nature of Chemical Energy 5.2 The First Law of Thermodynamics 5.3 Enthalpy 5.4 Enthalpies of Reaction...

Lecture #4, p. 1 Lecture 4: Announcements Today: Brown 5.1 The Nature of Chemical Energy 5.2 The First Law of Thermodynamics 5.3 Enthalpy 5.4 Enthalpies of Reaction 5.5 Calorimetry 5.6 Hess’s Law 5.7 Enthalpies of Formation Problem Set 3: Due before Exercise #4 tomorrow; upload on Moodle link Problem Set 4: Posted on Moodle; due before Exercise #5 next week Study Center: Wednesdays 18:00–20:00 in ETA F 5 Office Hours: Prof. Norris and Brisby, Thursdays 17:00–18:00 in LEE P 210 Chemistry  Lecture #4, p. 2 Lecture 5 Next Week: Brown 19.1 Spontaneous Processes 19.2 Entropy and the Second Law of Thermodynamics 19.3 The Molecular Interpretation of Entropy and the Third Law of Thermodynamics 19.4 Entropy Changes in Chemical Reactions 19.5 Gibbs Free Energy 19.6 Free Energy and Temperature Chemistry  Lecture #4, p. 3 Review In Lecture 3, we discussed reactions in aqueous solutions Solutions = solute + solvent Aqueous solutions, electrolytes, nonelectrolytes Precipitation reactions, exchange reactions Molecular reaction, complete ionic reaction, net ionic reaction Acids, bases, neutralization reactions Oxidation–reduction reactions Oxidation numbers, oxidation state Activity series Concentration: molarity Chemistry  Lecture #4, p. 4 Today: Understanding Energy Hydrogen combustion? How much work? How much heat? How can we calculate? + Chemistry  Lecture #4, p. 5 Thermodynamics I Today we will begin our discussion of thermodynamics What is thermodynamics? Study of energy and its transformations Relates heat, work, and chemical reactions We will introduce... Laws of Thermodynamics, Enthalpy, Entropy Address why some reactions occur and others do not Today’s topic... Thermochemistry How chemical reactions produce or absorb heat Chemistry  Lecture #4, p. 6 dy na m thermo Energy We need to begin by discussing energy y studyof and energy transform at Two types: kinetic energy and potential energy seetutoria in exercise motion stored energy In chemistry, potential energy can be stored in chemical bonds To understand thermodynamics, we must quantify energy... Start with conservation of energy 1st Law of Thermodynamics Energy can be converted between different types But it cannot be created or destroyed We will distinguish between... system and surroundings reactants and products everything else Chemistry  Lecture #4, p. 7 System Types Filing Open Matter and energy can be exchanged with surroundings pot ex Closed Energy can be exchanged with surroundings (but not matter) acomas pist sealed Isolated Neither matter nor energy is exchanged with surroundings thermally insulate Has Chemistry  Lecture #4, p. 8 edefine etotal Total Energy for System rayofour system Internal Energy, E Total kinetic plus potential energy in system Typically, we do not know actual value of E Instead, we focus on changes in E ∆" = "!"#$% − ""#"&"$% After and before “something” happened to system Usually, a chemical reaction Chemistry  Lecture #4, p. 9 Energy Changes ∆" = "!"#$% − ""#"&"$% Sign is important! ∆" > 0 system has gained energy surround ∆" < 0 system has lost energy For chemical reaction, !!"#$% is for products and !"#"&"$% is for reactants Energy Diagram " 2 H2 (g) + O2 (g) !"#"&"$% reactants Ex: 2 H2 (g) + O2 (g) 2 H2O (l) reaction ∆! < 0 Energy released to surroundings 2 H2O (l) !!"#$% products Chemistry  Lecture #4, p. 10 1st Law Revisited As energy cannot be created or destroyed, it must go somewhere! ∆" = ( + * ( ≡ heat added to system * ≡ work done on system Recall that % = ' ( ) (work is a force applied over a distance) So pushing a piston does work! Sign convention + means ! of our system has increased rtunatef s isnot (>0 heat added to system *>0 work done on system only sign mention rthe (