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Catalyst. Come in quietly and begin working on the Quiz that is on your desk. End. Learning Log Assessment. Rate yourself 1 – 4 on LTs 7.1-7.7. Checklist Manifesto!. How do I know which equation to use? Does it have specific heat or enthalpy?? Then use calorimetry!
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Catalyst Come in quietly and begin working on the Quiz that is on your desk End
Learning Log Assessment • Rate yourself 1 – 4 on LTs 7.1-7.7
Checklist Manifesto! • How do I know which equation to use? • Does it have specific heat or enthalpy?? • Then use calorimetry! • Does it give you ΔH or ΔT • If ΔH then use q = mΔH • If ΔT then use q = m x Cp x ΔT • Box the one it’s asking you to find! • Plug in the right numbers and solve!
Today’s Learning Targets • 7.8 – I can discuss what entropy is, the conditions under which it is favored, and how entropy changes when we change the phase of a solution. • 7.9 – I can describe what enthalpy is, how it relates to the idea of endothermic and exothermic, and how it changes the favorability of a reaction. • 7.10 – I can use the idea of Gibbs Free Energy to predict whether a reaction will be spontaneous.
Today’s Focus Question • What chemistry allows for the breakdown of Flamin’ Hot Cheetos to occur?
Exothermic Endothermic
I. Entropy and Enthalpy • Enthalpy is a measure of energy a system has. • Endothermic= +ΔH • Exothermic= -ΔH • Entropy is the measurement of the disorder of a system. • Lots of Disorder = +ΔS • Minimal Disorder = -ΔS
I. Favorability of Reactions • Only certain values of ΔH and ΔS are favorable • Reactions favor disorder, so +ΔS is favored. • Reactions favor reactions that release energy, so –ΔH is favored.
Class Example • Without calculating, predict if the following reaction will be spontaneous. If it is spontaneous, specify under what conditions. You run the following reaction: N2 (g) + O2(g) 2 NO (g) You have ΔH = 180.7 kJ and ΔS = 24.7 J/K
Table Talk • Without calculating, predict if the following reaction will be spontaneous. If it is spontaneous, specify under what conditions. • You run the following reaction: • P4 (g) + 6 Cl2 (g) 4 PCl3 (g) • You have ΔH = -190.2 kJ and ΔS = 423.4 J/K
Stop and Jot • Without calculating, predict if the following reaction will be spontaneous. If it is spontaneous, specify under what conditions. • You run the following reaction: • N2 (g) + 3 H2 (g) 2 NH3 (g) + 567 kJ
White Board Questions • Using only the signs of Ho and So, predict the signs and temperature dependence. • CH3OH (l) + 3/2 O2 (g) CO2 (g) + 2 H2O (g) • Exothermic reaction • 2. The vaporization of water • 3. CO (g) + H2O (g) CO2 (g) + H2 (g) • Ho = -41.2 kJ and So = -135 J/K • 4. The condensation of water • 5. P4 (g) + 6 Cl2 (g) 4 PCl3 (g) • The reaction is endothermic • 6. N2 (g) + O2(g) 2 NO (g) • The reaction is endothermic • 7. The freezing of carbon dioxide
I. Gibbs Free Energy (ΔG) • We can calculate ΔG by: ΔG = ΔH – TΔS • ΔG is the Gibbs Free Energy • T is Temperature (in KELVIN) • A positive ΔG means the reaction is NOT spontaneous. • A negative ΔG means that the reaction IS spontaneous
Class Example • For the vaporization reaction: Br2 (l) Br2 (g) ΔH = 31 kJ/mol and ΔS = 93 kJ/(mol x K). Is this spontaneous at 298 K?
Table Talk • A reaction has ΔH = -385 kJ and ΔS = -36 kJ/(mol x K). Calculate ΔG at 25 oC and state whether the reaction is spontaneous.
Stop and Jot • You have a reaction with a ΔH = 125 kJ/mol, ΔS = 0.0350 kJ/(mol x K), and T=293 K. Is this spontaneous and how could you make this reaction spontaneous?
BINGO Questions • I have a reaction with a positive enthalpy and a negative entropy. Is this a spontaneous or non-spontaneous reaction? • I have a reaction with a negative enthalpy and a positive entropy. Is this a spontaneous or non-spontaneous reaction? • I turn solid ice into liquid water. Does this increase or decrease the entropy of the system? • Determine the ΔG of the hydrolysis of urea when it is 25 oC, ΔH=119.2 kJ/mol, and ΔS=0.3548 kJ/(mol x K).
BINGO Questions • Calculate ΔG for the following reaction: ΔH = -85.2 kJ, T= 127 oC, and ΔS = 0.125 kJ/(mol x K). • Calculate ΔG for the following reaction: ΔH = -275 kJ, T= 773 oC, and ΔS = 0.450 kJ/(mol x K). • A reaction has ΔH = 98 kJ/mol and ΔS = 292 J/(mol x K). If the temperature is 25 oC, what is the ΔG? • For the vaporization reaction Br2 (l) Br2 (g) ΔH = 31 kJ/mol and ΔS = 93 kJ/(mol x K). At what temperature will it become spontaneous?
BINGO Questions • Which is more favorable: more disorder or less disorder? • Which is more favorable: an exothermic reaction or an endothermic reaction?
Learning Log Assessment • Rate yourself 1 – 4 on LTs 7.8, 7.9, and 7.10.
Online Simulator • Use the online simulator to explore the relationship between entropy, enthalpy and the favorability of a reaction. • You may work with a partner
Work Time • Begin working on your “Homework 7.5” • There will be an exit slip after this activity
Exit Slip 1. You have a reaction that has a +ΔS and a +ΔH. Under what conditions would this reaction be spontaneous? 2. For the reaction: NH4Cl (s) NH3 (g) + HCl (g) ΔH = 176 kJ/mol and ΔS=0.285 kJ/(mol x K) and T = 400 K. Determine ΔG and state whether this is a spontaneous reaction.
Learning Log Assessment • Using your exit slip score, re-rate yourself on LTs 7.8, 7.9, and 7.10
Review Stations • Station 1 – LT 7.1 • Station 2 – LT 7.2 • Station 3 – LT 7.3 • Station 4 – LT 7.4 • Station 5 – LT 7.5 • Station 6 – LT 7.6 • Station 7 – LT 7.7 • Rotate between the 7 stations (10 for honors) • Honors Station 8,9,10 – LT 7.8, 7.9, 7.10 ROTATE!
Closing Time • Homework 7.5 – Gibbs Free Energy • Test Tuesday!