Lecture 16 Thermdynamics II Calrimetry Hess s Law Enthalpy r Frmatin Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.
Fur Methds fr Finding H 1) Calculate it using average bnd enthalpies 2) Measure it using a calrimeter. 3) Calculate it using Hess s Law. 4) Calculate it using enthalpies f frmatin Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.
Calrimetry Calrimetry The measurement f heat transfer Calrimeter A device used t determine the amunt f heat transferred Heat flw cannt be measured directly. We measure the temperature befre and after a reactin, and use that data t calculate heat transfer. Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.
Calrimetry Specific Heat Capacity (c) The amunt f heat reuired t raise the temperature f 1 g f a substance by 1 K. A large value fr water (4.184 J/g K) It takes a lt f heat t increase the temperature f water. A small value fr irn (0.45 J/g K) It takes much less heat t raise the temperature f irn. Heat lst r gained by a substance = m c T Mass f that substance Specific heat capacity f that substance Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved. Temperature change f that substance T = T f - T i
Cffee Cup Calrimeter Thermmeter Stir Stick Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.
Cffee Cup Calrimetry When measuring the heat lst r gained in a chemical reactin that takes place in a cffee cup calrimeter, we use the slutin as the basis fr ur calculatins. = m c T Heat lst r gained by the slutin in the reactin Mass f the slutin Specific heat f the slutin 4.184 J/g K is ften used if cncentratins are lw. Temperature change f the slutin T = T f - T i Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.
Cffee Cup Calrimetry The reactants and prducts are the system. The water which they are disslved in and calrimeter make up the surrundings. The heat lst r gained by the slutin is eual t the heat lst r gained by the reactin. e.g.) If yu calculated slutin t be +568 J, the slutin gained heat. This means the reactin was exthermic, as the heat gained by the slutin is eual t the heat lst by the reactin ( rxn = -568 J). Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.
Ex1) Calrimetry Ex1) A 97 g irn bar was heated t 143 C and placed in a cffee cup calrimeter cntaining 350.0 g f water at 25.00 C. The maximum temperature f the water was measured t be 28.40 C. a) Hw much heat was gained by the water? b) Hw much heat was lst by the irn bar? c) What is the specific heat f irn? Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.
Ex1) Calrimetry (cnt.) a) Hw much heat was gained by the water? b) Hw much heat was lst by the irn bar? Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.
a) Hw much heat was gained by the water? w Ex1) Calrimetry (cnt.) = mc T b) Hw much heat was lst by the irn bar? Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.
Ex1) Calrimetry (cnt.) a) Hw much heat was gained by the water? w w = mc T (350.0 g)(4.184 J / g C)(28.40 C 25.00 C) = b) Hw much heat was lst by the irn bar? Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.
Ex1) Calrimetry (cnt.) a) Hw much heat was gained by the water? w w w = mc T (350.0 g)(4.184 J / g C)(28.40 C 25.00 C) = = + 4979 J Gaining heat is endthermic b) Hw much heat was lst by the irn bar? Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.
Ex1) Calrimetry (cnt.) a) Hw much heat was gained by the water? w w w = mc T (350.0 g)(4.184 J / g C)(28.40 C 25.00 C) = = + 4979 J b) Hw much heat was lst by the irn bar? w = Fe Gaining heat is endthermic Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.
Ex1) Calrimetry (cnt.) a) Hw much heat was gained by the water? w w w = mc T (350.0 g)(4.184 J / g C)(28.40 C 25.00 C) = = + 4979 J b) Hw much heat was lst by the irn bar? w Fe = Fe = 4979 J Gaining heat is endthermic Lsing heat is exthermic As energy is cnserved, the heat gained by the water is eual in magnitude t the heat lst by the irn bar. Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.
Ex1) Calrimetry (cnt.) c) What is the specific heat f irn? Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.
Ex1) Calrimetry (cnt.) c) What is the specific heat f irn? Fe = mc T Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.
Ex1) Calrimetry (cnt.) c) What is the specific heat f irn? Fe c = mc T Fe = m T Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.
Ex1) Calrimetry (cnt.) c) What is the specific heat f irn? Fe c c = mc T Fe = m T = 4979 J (97 g)(28.40 C 143 C) Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.
Ex1) Calrimetry (cnt.) c) What is the specific heat f irn? Fe c c c = mc T Fe = m T = (97 g)(28.40 C 143 C) = 0.45 J / g C 4979 J Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.
Ex2) Calrimetry Ex2) When 20.0 ml f 1.00 M NaCl at 22.00 C is mixed with 20.0 ml f 1.00 M AgNO 3 at 22.00 C in a calrimeter, a white precipitate frms and the temperature f the mixture reaches 29.60 C. Assume that the specific heat capacity f the mixture is 4.184 J/g K, its density is 1.00 g/ml, and the vlumes are additive. a) Write the net inic euatin fr this reactin. b) Calculate ΔH fr the reactin. Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.
Ex2) Calrimetry Ex2) When 20.0 ml f 1.00 M NaCl at 22.00 C is mixed with 20.0 ml f 1.00 M AgNO 3 at 22.00 C in a calrimeter, a white precipitate frms and the temperature f the mixture reaches 29.60 C. Assume that the specific heat capacity f the mixture is 4.184 J/g K, its density is 1.00 g/ml, and the vlumes are additive. a) Write the net inic euatin fr this reactin. b) Calculate ΔH fr the reactin. Ag + (a) + Cl - (a) AgCl (s) Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.
Ex2) Calrimetry (cnt.) Step 1) Calculate sl. Step 2) Calculate rxn. Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.
Step 1) Calculate sl. sl Ex2) Calrimetry (cnt.) = mc T Step 2) Calculate rxn. Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.
Ex2) Calrimetry (cnt.) Step 1) Calculate sl. sl sl = mc T (40.0 g)(4.184 J / g C)(29.60 C 22.00 C) = Step 2) Calculate rxn. Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.
Ex2) Calrimetry (cnt.) Step 1) Calculate sl. sl sl sl = mc T (40.0 g)(4.184 J / g C)(29.60 C 22.00 C) = (40.0 g)(4.184 J / g C)(7.60 C) = Step 2) Calculate rxn. Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.
Ex2) Calrimetry (cnt.) Step 1) Calculate sl. sl sl sl sl = mc T (40.0 g)(4.184 J / g C)(29.60 C 22.00 C) = (40.0 g)(4.184 J / g C)(7.60 C) = = + 1270 J Step 2) Calculate rxn. Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.
Ex2) Calrimetry (cnt.) Step 1) Calculate sl. sl sl sl sl = mc T (40.0 g)(4.184 J / g C)(29.60 C 22.00 C) = (40.0 g)(4.184 J / g C)(7.60 C) = = + 1270 J Step 2) Calculate rxn. rxn rxn = sl = 1270 J The reactin is exthermic as heat is released t the water. Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.
Ex2) Calrimetry (cnt.) Step 3) Calculate Mles f Ag + r Cl -. Step 4) Calculate ΔH rxn. Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.
Ex2) Calrimetry (cnt.) Step 3) Calculate Mles f Ag + r Cl -. + 1.0 mles Ag 0.0200 L = 0.0200 mles Ag 1 L Step 4) Calculate ΔH rxn. + Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.
Ex2) Calrimetry (cnt.) Step 3) Calculate Mles f Ag + r Cl -. + 1.0 mles Ag 0.0200 L = 0.0200 mles Ag 1 L Step 4) Calculate ΔH rxn. H = rxn H = rxn n rxn AgCl 1270 J 0.0200 mles AgCl + Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.
Ex2) Calrimetry (cnt.) Step 3) Calculate Mles f Ag + r Cl -. + 1.0 mles Ag 0.0200 L = 0.0200 mles Ag 1 L Step 4) Calculate ΔH rxn. H = rxn H = rxn rxn AgCl 1270 J 0.0200 mles AgCl H = 63500 J/ml = 63.5 kj/ml rxn n Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved. +
rxn vs. H rxn rxn = The heat lst r gained in the experiment that tk place in the calrimeter H rxn = The heat lst r gained in the balanced chemical euatin Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.
Fur Methds fr Finding H 1) Calculate it using average bnd enthalpies. 2) Measure it using a calrimeter. 3) Calculate it using Hess s Law. 4) Calculate it using enthalpies f frmatin. Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.
Hess s Law If a reactin is carried ut in a series f steps, the verall change in enthalpy will be eual t the sum f the enthalpy changes fr the individual steps. The verall enthalpy change will be the same if a reactin is carried ut in ne step r in several steps. Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.
Ex1) Hess s Law Ex1) Calculate H fr the fllwing reactin using the infrmatin in the table belw. 4 NO 2(g) + O 2(g) 2 N 2 O 5(s) Reactin Chemical Euatin Enthalpy Change 1 2 NO (g) + O 2(g) N 2 O 5(s) H = - 223.7 kj 3 2 2 2 NO (g) + O 2(g) 2 NO 2(g) H = - 114.2 kj Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.
Ex1) Hess s Law (cnt.) Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.
Ex1) Hess s Law (cnt.) 2(rxn 1) 4 NO (g) + 3 O 2(g) 2 N 2 O 5(s) H = 2(- 223.7 kj) Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.
Ex1) Hess s Law (cnt.) 2(rxn 1) 4 NO (g) + 3 O 2(g) 2 N 2 O 5(s) -2(rxn 2) 4 NO 2(g) 4 NO (g) + 2 O 2(g) H = 2(- 223.7 kj) H = -2(-114.2 kj) Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.
Ex1) Hess s Law (cnt.) 2(rxn 1) 4 NO (g) + 3 O 2(g) 2 N 2 O 5(s) -2(rxn 2) 4 NO 2(g) 4 NO (g) + 2 O 2(g) H = 2(- 223.7 kj) H = -2(-114.2 kj) Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.
Ex1) Hess s Law (cnt.) 2(rxn 1) 4 NO (g) + 3 O 2(g) 2 N 2 O 5(s) -2(rxn 2) 4 NO 2(g) 4 NO (g) + 2 O 2(g) H = 2(- 223.7 kj) H = -2(-114.2 kj) 4 NO 2(g) + O 2(g) 2 N 2 O 5(s) H = -219.0 kj Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.
Ex2) Hess s Law Ex2) Calculate H fr the fllwing reactin using the infrmatin in the table belw. 3 C (s) + 4 H 2(g) C 3 H 8(g) Reactin Chemical Euatin Enthalpy Change 1 2 H 2(g) + O 2(g) 2 H 2 O (l) H = - 571.7 kj 2 C 3 H 8(g) + 5O 2(g) 3CO 2(g) + 4H 2 O (l) H = - 2220.1 kj 3 C (s) + O 2(g) CO 2(g) H = - 393.5 kj Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.
Ex2) Hess s Law (cnt.) 2(rxn 1) 4 H 2(g) + 2 O 2(g) 4 H 2 O (l) H = 2(- 571.7 kj) Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.
Ex2) Hess s Law (cnt.) 2(rxn 1) 4 H 2(g) + 2 O 2(g) 4 H 2 O (l) H = 2(- 571.7 kj) -1(rxn 2) 3 CO 2(g) + 4 H 2 O (l) C 3 H 8(g) + 5 O 2(g) H = - (-2220.1kJ) Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.
Ex2) Hess s Law (cnt.) 2(rxn 1) 4 H 2(g) + 2 O 2(g) 4 H 2 O (l) H = 2(- 571.7 kj) -1(rxn 2) 3 CO 2(g) + 4 H 2 O (l) C 3 H 8(g) + 5 O 2(g) H = - (-2220.1kJ) 3(rxn 3) 3 C (s) + 3 O 2(g) 3 CO 2(g) H = 3(- 393.5 kj) Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.
Ex2) Hess s Law (cnt.) 2(rxn 1) 4 H 2(g) + 2 O 2(g) 4 H 2 O (l) H = 2(- 571.7 kj) -1(rxn 2) 3 CO 2(g) + 4 H 2 O (l) C 3 H 8(g) + 5 O 2(g) H = - (-2220.1kJ) 3(rxn 3) 3 C (s) + 3 O 2(g) 3 CO 2(g) H = 3(- 393.5 kj) 3 C (s) + 4 H 2(g) C 3 H 8(g) H = -103.8 kj Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.
Fur Methds fr Finding H 1) Calculate it using average bnd enthalpies. 2) Measure it using a calrimeter. 3) Calculate it using Hess s Law. 4) Calculate it using enthalpies f frmatin. Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.
Standard Enthalpy f Frmatin A hypthetical value that indicates hw much heat wuld be lst r gained during the frmatin f ne mle f a cmpund frm the mst cmmn frm f its elements in their standard states. H f standard state (25 C, 1 atm) Frmatin Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.
Standard Enthalpy f Frmatin Fr Methanl C (s) + 2 H 2(g) + ½ O 2(g) CH 3 OH (g) H f = -201 kj/ml Heat f frmatin reactins are always written s that all reactants exist as they wuld under standard cnditins, and there is ne mle f prduct. Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.
Enthalpy f Frmatin The H f value fr the mst stable frm f any element in its standard state is zer. Element H f Element H Ca(s) 0 Cl 2 (g) 0 Ag(s) 0 H 2 (g) 0 Na(s) 0 Fe(s) 0 O 2 (g) 0 N 2 (g) 0 f Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.
Frmula fr Calculating the Enthalpy f a Reactin under Standard Cnditins H rxn f = Σ n H (prducts) Σ n H (reactants) f Sum f stichimetric cefficients Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.
Ex1) Enthalpy f Frmatin Ex1) Find H rxn fr the thermite reactin under standard cnditins. H Fe 2 O 3(s) + 2 Al (s) 2 Fe (s) + Al 2 O 3(s) = Σ n H (prducts) Σ n H (reactants) H rxn = [2 ( H f (Fe (s) )) + 1 ( H f (Al 2 O 3(s) ))] [2 ( H (Al (s) )) + 1 ( H (Fe 2 O 3(s) ))] H = [2(0) + 1(-1675.7)] - [2(0) + 1(-821.4)] H rxn rxn rxn f f = - 854.3 kj/ml f f Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.
Ex2) Enthalpy f Frmatin Ex2) Find H cnditins. rxn fr this reactin at standard H rxn 2 H 2 S (g) + 3 O 2(g) 2 SO 2(g) + 2 H 2 O (g) f = Σ n H (prducts) Σ n H (reactants) f Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.
Ex2) Enthalpy f Frmatin Ex2) Find H cnditins. rxn fr this reactin at standard H rxn 2 H 2 S (g) + 3 O 2(g) 2 SO 2(g) + 2 H 2 O (g) f = Σ n H (prducts) - Σ n H (reactants) H rxn = [2 ( H f (SO 2(g) )) + 2 ( H f (H 2 O (g) ))] [2 ( H (H 2 S (g) )) + 3 ( H (O 2(g) ))] f f f Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.
Ex2) Enthalpy f Frmatin Ex2) Find H cnditins. rxn fr this reactin at standard H 2 H 2 S (g) + 3 O 2(g) 2 SO 2(g) + 2 H 2 O (g) = Σ n H (prducts) - Σ n H (reactants) H rxn = [2 ( H f (SO 2(g) )) + 2 ( H f (H 2 O (g) ))] [2 ( H (H 2 S (g) )) + 3 ( H (O 2(g) ))] H = [2(-296.8) + 2(-241.8)] - [2(-20.2) + 3(0)] H rxn rxn rxn f f = - 1036.8 kj/ml f f Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.
Enthalpy f Frmatin Reactin H f kj/ml Elemental metal 1 st used by humans 2 Au (s) + 3/2 O 2 (g) Au 2 O 3(s) +131 ~6000 BCE 2 Ag (s) + 1/2 O 2 (g) Ag 2 O (s) 31 ~4000 BCE Cu (s) + 1/2 O 2 (g) CuO (s) 156 ~4000 BCE Pb (s) + 1/2 O 2 (g) PbO (s) 217 ~3500 BCE Sn (s) + O 2 (g) SnO 2(s) 581 ~1800 BCE 2 Fe (s) + 3/2 O 2 (g) Fe 2 O 3(s) 822 ~1200 BCE Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.
Ex3) Enthalpy f Frmatin Ex3) Use the enthalpy f frmatin values belw t determine ΔH rxn fr the reactin between C (s) and Fe 2 O 3(s) t prduce Fe (s). 2 Fe (s) + 3/2 O 2 (g) Fe 2 O 3(s) C (s) + O 2 (g) CO 2(s) = 822 kj/ml H f = 394 kj/ml H f Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.
Ex3) Enthalpy f Frmatin Ex3) Use the enthalpy f frmatin values belw t determine ΔH rxn fr the reactin between C (s) and Fe 2 O 3(s) t prduce Fe (s). 2 Fe (s) + 3/2 O 2 (g) Fe 2 O 3(s) C (s) + O 2 (g) CO 2(s) = 822 kj/ml H f = 394 kj/ml H f 2(rxn 1) 2 Fe 2 O 3(s) 4 Fe (s) + 3 O 2 (g) H = 2( 822 kj) Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.
Ex3) Enthalpy f Frmatin Ex3) Use the enthalpy f frmatin values belw t determine ΔH rxn fr the reactin between C (s) and Fe 2 O 3(s) t prduce Fe (s). 2 Fe (s) + 3/2 O 2 (g) Fe 2 O 3(s) C (s) + O 2 (g) CO 2(s) = 822 kj/ml H f = 394 kj/ml H f 2(rxn 1) 2 Fe 2 O 3(s) 4 Fe (s) + 3 O 2 (g) H = 2( 822 kj) 3(rxn 2) 3 C (s) + 3 O 2 (g) 3 CO 2(s) H = 3( 394 kj) Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.
Ex3) Enthalpy f Frmatin Ex3) Use the enthalpy f frmatin values belw t determine ΔH rxn fr the reactin between C (s) and Fe 2 O 3(s) t prduce Fe (s). 2 Fe (s) + 3/2 O 2 (g) Fe 2 O 3(s) C (s) + O 2 (g) CO 2(s) = 822 kj/ml H f = 394 kj/ml H f 2(rxn 1) 2 Fe 2 O 3(s) 4 Fe (s) + 3 O 2 (g) H = 2( 822 kj) 3(rxn 2) 3 C (s) + 3 O 2 (g) 3 CO 2(s) H = 3( 394 kj) 2 Fe 2 O 3(s) + 3 C (s) 4 Fe (s) + 3 CO 2(s) H = + 462 kj Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.
Ex) Enthalpy and Stichimetry 2 H 2 O 2(a) O 2(g) + 2 H 2 O (l) H = -186 kj Ex) Hw much heat is released when 3.56 g H 2 O 2(a) decmpses int water and xygen gas? 1 ml H O 186 kj 2 2 3.56g H2O 2 = 9.73 kj 34.02 g H2O2 2 ml H2O2 There are 2 mles H 2 O 2 in the balanced euatin. Cpyright 2013, 2011, 2009, 2008 AP Chem Slutins. All rights reserved.