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

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 C p x ΔT  Box the one it’s asking you to find!  Plug in the right numbers and solve!

Connect 4

Lecture 7.5 – Gibbs Free Energy

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 – 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?

What are enthalpy and entropy?

Endothermic Exothermic

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

How do we predict spontaneous reactions?

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.

+ΔH-ΔH +ΔSSometime Spontaneous (High Temp. Required) Always Spontaneous -ΔSNever Spontaneous Sometimes Spontaneous (Low Temp. Required)

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: N 2 (g) + O 2 (g)  2 NO (g) You have ΔH = 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: P 4 (g) + 6 Cl 2 (g)  4 PCl 3 (g) You have ΔH = kJ and ΔS = 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: N 2 (g) + 3 H 2 (g)  2 NH 3 (g) kJ

White Board Races

White Board Questions Using only the signs of  H o and  S o, predict the signs and temperature dependence. 1.CH 3 OH (l) + 3/2 O 2 (g)  CO 2 (g) + 2 H 2 O (g) Exothermic reaction 2. The vaporization of water 3. CO (g) + H 2 O (g)  CO 2 (g) + H 2 (g)  H o = kJ and  S o = -135 J/K 4. The condensation of water 5. P 4 (g) + 6 Cl 2 (g)  4 PCl 3 (g) The reaction is endothermic 6. N 2 (g) + O 2 (g)  2 NO (g) The reaction is endothermic 7. The freezing of carbon dioxide

How do we calculate spontaneity?

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: Br 2 (l)  Br 2 (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 o C and state whether the reaction is spontaneous.

Stop and Jot You have a reaction with a ΔH = 125 kJ/mol, ΔS = kJ/(mol x K), and T=293 K. Is this spontaneous and how could you make this reaction spontaneous?

BINGO! Below 333 KSpontaneousEndothermic Decrease Entropy kJ Not Spontaneous 13.5 kJ13.4 kJ Increase Entropy kJ/molAbove 333 KLess Disorder More DisorderExothermic11,000 kJ11 kJ

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 o C, ΔH=119.2 kJ/mol, and ΔS= kJ/(mol x K).

BINGO Questions Calculate ΔG for the following reaction: ΔH = kJ, T= 127 o C, and ΔS = kJ/(mol x K). Calculate ΔG for the following reaction: ΔH = -275 kJ, T= 773 o C, and ΔS = kJ/(mol x K). A reaction has ΔH = 98 kJ/mol and ΔS = 292 J/(mol x K). If the temperature is 25 o C, what is the ΔG ? For the vaporization reaction Br 2 (l)  Br 2 (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

Begin working on your “Homework 7.5” There will be an exit slip after this activity Work Time

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: NH 4 Cl (s)  NH 3 (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 Rotate between the 7 stations (10 for honors) ROTATE! 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 Honors Station 8,9,10 – LT 7.8, 7.9, 7.10

Homework 7.5 – Gibbs Free Energy Test Tuesday! Closing Time