1 Energy and Thermochemistry

2 Energy The ability to do work The ability to do work 2 types 2 types Potential: stored energy Potential: stored energy Kinetic: energy in motion Kinetic: energy in motion

3 Thermochemistry Changes of heat content and heat transfer Changes of heat content and heat transfer Follow Law of Conservation of Energy Follow Law of Conservation of Energy Or, 1 st Law of Thermodynamics Or, 1 st Law of Thermodynamics Energy can neither be created nor destroyed Energy can neither be created nor destroyed

4 Temperature & Heat Heat not same as temperature Heat not same as temperature Heat = energy transferred to one system by another due to temperature difference Heat = energy transferred to one system by another due to temperature difference Temperature = measure of heat energy content & ability to transfer heat Temperature = measure of heat energy content & ability to transfer heat Thermometer Thermometer Higher thermal energy, greater motion of constituents Higher thermal energy, greater motion of constituents Sum of individual energies of constituents = total thermal energy Sum of individual energies of constituents = total thermal energy

5 Systems and Surroundings System = the object in question System = the object in question Surrounding(s) = everything outside the system Surrounding(s) = everything outside the system When both system and surrounding at same temperature  thermal equilibrium When both system and surrounding at same temperature  thermal equilibrium When not When not Heat transfer to surrounding = exothermic Heat transfer to surrounding = exothermic (you feel the heat)  hot metal! (you feel the heat)  hot metal! Heat transfer to system = endothermic Heat transfer to system = endothermic (you feel cold)  cold metal! (you feel cold)  cold metal!

6 Math! Joules (J) used for energy quantities Joules (J) used for energy quantities But usually kJ (1000 J) used But usually kJ (1000 J) used Ye Royal Olde School used calorie (cal) Ye Royal Olde School used calorie (cal) cal = amt of heat required to raise the temperature of 1.00 g of water by 1  C cal = amt of heat required to raise the temperature of 1.00 g of water by 1  C 1 cal = J (SI-unit) 1 cal = J (SI-unit) But…Calorie (Cal) = 1000 cal But…Calorie (Cal) = 1000 cal Used in nutrition science and on food labels Used in nutrition science and on food labels

7 Heat Capacity Specific heat capacity Specific heat capacity Quantity of heat required to raise the temp of 1 gram of any substance by 1 K Quantity of heat required to raise the temp of 1 gram of any substance by 1 K Molar heat capacity Molar heat capacity Quantity of heat required to raise the temp of 1 mole of any substance by 1 K

8 Calculating heat transfer FYI FYI Specific heat capacity of metals is very low Specific heat capacity of metals is very low  < J/(g  K)  < J/(g  K) What does this tell us about heat transfer in metals? What does this tell us about heat transfer in metals?

9 Let’s do an example In your backyard, you have a swimming pool that contains 5.19 x 10 3 kg of water. How many kJ are required to raise the temperature of this water from 7.2 °C to 25.0 °C? In your backyard, you have a swimming pool that contains 5.19 x 10 3 kg of water. How many kJ are required to raise the temperature of this water from 7.2 °C to 25.0 °C?

10 Example solved Trick:  T in K =  T in °C Trick:  T in K =  T in °C

11 Practice How many kJ are required to raise the temperature of 25.8 g of quicksilver from 22.5 °C to 28.0 °C? C Hg = J/(g  K) How many kJ are required to raise the temperature of 25.8 g of quicksilver from 22.5 °C to 28.0 °C? C Hg = J/(g  K)

12 Solution