2 Specific heat capacity (a.k.a. Specific heat) 3/27/2017Specific heat capacity (a.k.a. Specific heat)symbolized as c, units in J/gCIt’s the heat required to raise 1 gram of a substance by 1 CHeat capacitycalculated by c x m, units in J/CIt’s the heat required to raise the temperature of an object by 1 C.Molar heat capacitySimilar to specific heat capacity, but uses moles instead of grams, units in J/mol C.It’s the heat required to raise the temperature of 1 mol of a substance by 1 C
3 Answers 2. a) As calculated yesterday: 25.5 kJ 3/27/2017Answers2.a) As calculated yesterday: 25.5 kJb) Specific heat is 4.18 J/gC (pg. 151)c) Heat capacity: cm=4.18J/gCx200g=836 J/Cd) Molar heat capacity is c x g/mol=4.18 J/gC x 18 g/mol = 75.3 J/molC3. Simply using q=cmT,c= 4.18 J/gC, m=335 g, T= = 1.9Cq=cmT= 4.18 J/gC x 335 g x 1.9C = 2.7 kJ4. We cannot determine the c for wax from this data because we did not heat the candle (no value for T). We would have to change the lab procedure if we wanted c for wax.
4 q=cmT= 2.0 J/gC x 5 g x 60 C = 600 Jq=cmT,c=q/mT= 10 J /(3.1 g)(17.9C) = 0.18 J/gC (gold is J/gC - pg. 151; it is not pure)heat capacity = cm = 0.18 J/gC x 3.1 g= J/ C5.15: Something with a high c needs more energy to increase in temperature5.16: Something with a low c experiences a greater rise in temp. given the same energy5.18: The body is mostly water. Water (and the body) has a high c, thus a large change in energy will cause only a small shift in temp.
5 Crossword 8. negative 9. positive 11. grams 12. bomb 14. law of conservation of energy17. insulator18. endothermic19. oxygen20. water1. enthalpy change2. thermochemistry3. calorimeter4. heat of reaction5. exothermic6. out7. surroundings10. boundary13. enthalpy15. system16. coffeecup
6 9. Enthalpy (total energy) includes: chemical potential energy of chemicalsgravitational potential energykinetic energy (earth’s rotation, etc)heat energyWe cannot measure enthalpy because we cannot measure absolute gravitational or kinetic energy10.Any reaction that produces light, sound, kinetic energy (explosion), etc.
7 11.Thermometer identifies T of water. H is found using q=cmT and law of conservation of energy (technically, pressure must be constant for q to equal H)BoundaryEndothermicExothermicSystem
8 A basic calorimeter - see handout In our lab we tried to determine H via q from “calorimetry”. Here are some terms assoc-iated with calorimetry (and thermochemistry)Endothermic = absorbing energySurroundings everything elseSystem with can as boundaryExothermic = releasing energyLaw of conservation of energy = release and absorption of energy must be equalFor more lessons, visit