Question

Thermodynamics Practice Problems 1. Predict the sign of AS.(positive or negative) for the following reactions a 2 Mg(s) +,(@) 2 Mgo (s) AS b. CH206(s) → 2C,H,OH(I) + 2003(g) AS c. 2 NH3(g) + CO2(g) → H2O(l) + NH CONH3(aq) AS d. Cu(s) (at 100°C) → Cu(s) (at 25°C) AS 2. Which two variables can indicate if a reaction is spontaneous or not? 3. The second law of thermodynamics tells us that: a Energy is conserved. b. The entropy of a pure solid crystal at 0 Kelvin is zero. C. The total enthalpy of the universe is increasing. d. The total entropy of a spontaneous process is increasing e. The free energy of a spontaneous process is increasing 4. Which combination of AH and AS for a reaction is not spontaneous at low temperatures and becomes spontaneous at higher temperatures? Answer: AH_ and AS 5. The process of a liquid boiling has a: a. Positive enthalpy change and a positive entropy change. b. Positive enthalpy change and a negative entropy change. C. Negative enthalpy change and a positive entropy change. d. Negative enthalpy change and a negative entropy change. e. Not enough information is given 6. Calculate the temperature at which this reaction changes from being spontaneous to non spontaneous: Mg(s) + Ox® 5 MgO(*). Is the reaction spontaneous above or below this temperature? (Hint - balance the non and use data from Appendix B) 7. Calculate AGⓇ for this reaction: 2 CH,OH (1) +3 O2(g) → 2 CO, () + 4H20 (1) Given: AH; CH3OH (I) = -238.6 kJ/mol AHH:0 (1) = -285.83 kJ/mol SCH,OH (1) = 126.8 J/molk AHCO, (g) = -393.5 kJ/mol sº O2(g) = 205.0J/molk sº CO2 (g) = 213.6 J/molk SH,0 (1) = 69.91 J/molk (only use this given data for your answer)

Answer 1

There is a relationship between entropy (5) Of a system & number of microstate ) possible for a system. S-klad here, k = Boltzmann constant 1.38x10 3/4 The microstate ( ) is a specific configuration of locations of energires. of the atoms or the molecules Since, is in a state function. So, change of entropy in differenca och final entropy (ip) of initial entropy (5) 45 F S – Si - klart, – k en die k en (de ) 2.1) when for a proces ahen das die then uso & when dag d. then ASLO During phase change from solid to as then number of microstote states increase. So, entropy aho increases, Soolid < Siquid K Sgas when number of moles in a reaction increases arith respect to reactante then the mi erontotes 2 increase & As become elve. But when nun of moles de creases then as become Eive. to liquid liqud &

Aml for the given reaction 6 2 ngist 02 (8) - 2ngo ks) here, reactants: 2 mol solid & mot gan. Products : 2 mol solid Initial mole Final - change = se Products Recitants = 2mwysolid - 2mb solid . - /ano pas = – mogen So, here, & drinn ere.. fb) tros (6) 262 45 OH (l) + 2002 (9) here, an & 2 moles lig 2 moles gan - 1 mol solid Here total number of moles increase & since gr sua & Soolid So, shorn - elve (c) 2NH3 (1) + cor) – #206) + With CONR An - wat lig & mat og i.e.ua - Bendengar gases species decreasing so, 4 ore also decrease. ... 4. Soon – ve. (6) Cu (6) Cat 180c) Cu (8) (at 256) Here at higher temperature due to more excitation of in vibration estate the number of microstate (2) acill increase So, then temperature decrease th similarly 2 will decrease eture teve tempera à decreasing. so A Sorm Elve. earen then