Presentation on theme: "Specific heat capacity (a.k.a. Specific heat) symbolized as c, units in J/g C Its the heat required to raise 1 gram of a substance by 1 C Heat capacity."— Presentation transcript:
Specific heat capacity (a.k.a. Specific heat) symbolized as c, units in J/g C Its the heat required to raise 1 gram of a substance by 1 C Heat capacity calculated by c x m, units in J/ C Its the heat required to raise the temperature of an object by 1 C. Molar heat capacity Similar to specific heat capacity, but uses moles instead of grams, units in J/mol C. Its the heat required to raise the temperature of 1 mol of a substance by 1 C
Answers 2. a) As calculated yesterday: 25.5 kJ b) Specific heat is 4.18 J/g C (pg. 151) c) Heat capacity: cm=4.18J/g Cx200g=836 J/ C d) Molar heat capacity is c x g/mol =4.18 J/g C x 18 g/mol = 75.3 J/mol C 3. Simply using q=cm T, c= 4.18 J/g C, m=335 g, T= = 1.9 C q=cm T= 4.18 J/g C x 335 g x 1.9 C = 2.7 kJ 4. 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.
5.q=cm T= 2.0 J/g C x 5 g x 60 C = 600 J 6.q=cm T, c=q/m T= 10 J /(3.1 g)(17.9 C) = 0.18 J/g C (gold is J/g C - pg. 151; it is not pure) heat capacity = cm = 0.18 J/g C x 3.1 g = J/ C 5.15: Something with a high c needs more energy to increase in temperature 5.16: Something with a low c experiences a greater rise in temp. given the same energy 5.18: 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.
Crossword 8. negative 9. positive 11. grams 12. bomb 14.law of conservation of energy 17.insulator 18.endothermic 19.oxygen 20.water 1. enthalpy change 2. thermochemistry 3. calorimeter 4. heat of reaction 5. exothermic 6.out 7.surroundings 10.boundary 13.enthalpy 15.system 16.coffeecup
9.Enthalpy (total energy) includes: chemical potential energy of chemicals gravitational potential energy kinetic energy (earths rotation, etc) heat energy We cannot measure enthalpy because we cannot measure absolute gravitational or kinetic energy 10.Any reaction that produces light, sound, kinetic energy (explosion), etc.
11. BoundaryEndothermic Exothermic Thermometer identifies T of water. H is found using q=cm T and law of conservation of energy (technically, pressure must be constant for q to equal H) System
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 energy Law of conservation of energy = release and absorption of energy must be equal Surroundings everything else Exothermic = releasing energy System with can as boundary For more lessons, visit