As always… OWL Lon-Capa assignments Lecture videos Textbook Read Do text homework

Office Hours 3014 Chemistry Annex decoste@illinois.edu 11am-12pm Mondays and Wednesdays (after lecture) 10-11 am Tuesdays and 1-2 pm Thursdays By appointment; open-door policy

To Improve: The Obvious Lecture Attend. Textbook Read it and do the homework. Videos Watch them. Electronic Homework Do the assignments. Lon-Capa HW#1: 99% Lon-Capa HW#3: 92%

To Improve: The Less Obvious Lecture Be active (come prepared, ask questions). Textbook Read critically, before lecture (take notes, ask questions). Videos Watch critically, before lecture (take notes, ask questions). Electronic Homework Do the assignments as you learn about the material.

To Improve: The Not Obvious Change how you view homework. It is not just something to be over with. Change how you view studying. You are currently studying for the second exam whether you believe it or not. Change how you view learning. Do it for understanding not for points (and you’ll earn both!). Manage your time wisely. 3 am Lon-Capa?

NH4NO3(s)  NH4+(aq) + NO3–(aq) ΔH = 25.7 kJ Clicker Question A 5.014-g sample of NH4NO3(s) is dissolved in 50.00 mL of water with both substances initially at room temperature (24.7°C). Calculate the final temperature of the solution. You may make the following assumptions: no heat loss to the surroundings; the specific heat capacity of the solution is 4.18 J/g°C; and the density of water is 1.00 g/mL. NH4NO3(s)  NH4+(aq) + NO3–(aq) ΔH = 25.7 kJ   a) 17.0°C b) 17.7°C c) 31.7°C d) 32.4°C e) I cannot get any of these answers.

Determining Hrxn Since H = qp, determine the heat given off or required at constant pressure by measuring temperatures. This is termed calorimetry. Since energy is conserved, we can often determine Hrxn for one reaction given values of Hrxn for others. Uses the principle in Hess’s Law. Use standard enthalpies of formations for reactants and products (we have tables of these).

Hess’s Law Due to first law and H being a state function. If a reaction is reversed, the sign of H is also reversed The magnitude of ΔH is directly proportional to the quantities of reactants and products in a reaction. That is, if the coefficients in a balanced equation are multiplied by an integer, the value of H is multiplied by the same integer.

2NaHCO3(s)  Na2CO3(s) + CO2(g) + H2O(l) Clicker Question Baking soda can decompose to produce sodium carbonate, carbon dioxide, and water according to the following chemical equation: 2NaHCO3(s)  Na2CO3(s) + CO2(g) + H2O(l) Given the following data, determine ΔH° for the decomposition of baking soda as written above. Na2CO3(s) + 2HCl(aq)  2NaCl(aq) + CO2(g) + H2O(l) ΔH° = –28.9 kJ/mol NaHCO3(s) + HCl(aq)  NaCl(aq) + CO2(g) + H2O(l) ΔH° = 28.3 kJ/mol   a) –0.6 kJ b) 27.7 kJ c) 52.8 kJ d) 57.7 kJ e) 85.5 kJ

Determining Hrxn Since H = qp, determine the heat given off or required at constant pressure by measuring temperatures. This is termed calorimetry. Since energy is conserved, we can often determine Hrxn for one reaction given values of Hrxn for others. Uses the principle in Hess’s Law. Use standard enthalpies of formations for reactants and products (we have tables of these).

Clicker Question Using the following data, calculate the standard enthalpy of formation of the compound ICl(g), in kJ/mol:   H° (kJ/mol) Cl2(g)  2Cl(g) 242.3 I2 (g)  2I(g) 151.0 ICl(g)  I(g) + Cl(g) 211.3 I2(g)  I2(s) –62.8 a) –14.6 b) –29.3 c) –211 d) 16.8 e) 33.5